Parser.idr

module Idris.Parser

import Core.Options
import Core.Metadata
import Idris.Syntax
import Idris.Syntax.Traversals
import public Parser.Source
import TTImp.TTImp

import public Libraries.Text.Parser
import Data.Either
import Libraries.Data.IMaybe
import Data.List
import Data.List.Quantifiers
import Data.List1
import Data.Maybe
import Data.So
import Data.Nat
import Data.SnocList
import Data.String
import Libraries.Utils.String
import Libraries.Data.WithDefault

import Idris.Parser.Let

%default covering

decorate : OriginDesc -> Decoration -> Rule a -> Rule a
decorate fname decor rule = do
  res <- bounds rule
  actD (decorationFromBounded fname decor res)
  pure res.val

boundedNameDecoration : OriginDesc -> Decoration -> WithBounds Name -> ASemanticDecoration
boundedNameDecoration fname decor bstr = ((fname, start bstr, end bstr)
                                         , decor
                                         , Just bstr.val)

decorateBoundedNames : OriginDesc -> Decoration -> List (WithBounds Name) -> EmptyRule ()
decorateBoundedNames fname decor bns
  = act $ MkState (cast (map (boundedNameDecoration fname decor) bns)) []

decorateBoundedName : OriginDesc -> Decoration -> WithBounds Name -> EmptyRule ()
decorateBoundedName fname decor bn = actD (boundedNameDecoration fname decor bn)

decorateKeywords : OriginDesc -> List (WithBounds a) -> EmptyRule ()
decorateKeywords fname xs
  = act $ MkState (cast (map (decorationFromBounded fname Keyword) xs)) []

dependentDecorate : OriginDesc -> Rule a -> (a -> Decoration) -> Rule a
dependentDecorate fname rule decor = do
  res <- bounds rule
  actD (decorationFromBounded fname (decor res.val) res)
  pure res.val

decoratedKeyword : OriginDesc -> String -> Rule ()
decoratedKeyword fname kwd = decorate fname Keyword (keyword kwd)

decoratedPragma : OriginDesc -> String -> Rule ()
decoratedPragma fname prg = decorate fname Keyword (pragma prg)

decoratedSymbol : OriginDesc -> String -> Rule ()
decoratedSymbol fname smb = decorate fname Keyword (symbol smb)

decoratedNamespacedSymbol : OriginDesc -> String -> Rule (Maybe Namespace)
decoratedNamespacedSymbol fname smb =
  decorate fname Keyword $ namespacedSymbol smb

parens : {b : _} -> OriginDesc -> BRule b a -> Rule a
parens fname p
  = pure id <* decoratedSymbol fname "("
            <*> p
            <* decoratedSymbol fname ")"

decoratedDataTypeName : OriginDesc -> Rule Name
decoratedDataTypeName fname = decorate fname Typ dataTypeName

decoratedDataConstructorName : OriginDesc -> Rule Name
decoratedDataConstructorName fname = decorate fname Data dataConstructorName

decoratedSimpleBinderName : OriginDesc -> Rule String
decoratedSimpleBinderName fname = decorate fname Bound unqualifiedName

decoratedSimpleNamedArg : OriginDesc -> Rule String
decoratedSimpleNamedArg fname
  = decorate fname Bound unqualifiedName
  <|> parens fname (decorate fname Bound unqualifiedOperatorName)

-- Forward declare since they're used in the parser
topDecl : OriginDesc -> IndentInfo -> Rule (List PDecl)
collectDefs : List PDecl -> List PDecl

-- Some context for the parser
public export
record ParseOpts where
  constructor MkParseOpts
  eqOK : Bool -- = operator is parseable
  withOK : Bool -- = with applications are parseable

peq : ParseOpts -> ParseOpts
peq = { eqOK := True }

pnoeq : ParseOpts -> ParseOpts
pnoeq = { eqOK := False }

export
pdef : ParseOpts
pdef = MkParseOpts {eqOK = True, withOK = True}

pnowith : ParseOpts
pnowith = MkParseOpts {eqOK = True, withOK = False}

export
plhs : ParseOpts
plhs = MkParseOpts {eqOK = False, withOK = False}

%hide Prelude.(>>)
%hide Prelude.(>>=)
%hide Core.Core.(>>)
%hide Core.Core.(>>=)
%hide Prelude.pure
%hide Core.Core.pure
%hide Prelude.(<*>)
%hide Core.Core.(<*>)

atom : OriginDesc -> Rule PTerm
atom fname
    = do x <- bounds $ decorate fname Typ $ exactIdent "Type"
         pure (PType (boundToFC fname x))
  <|> do x <- bounds $ name
         pure (PRef (boundToFC fname x) x.val)
  <|> do x <- bounds $ dependentDecorate fname constant $ \c =>
                       if isPrimType c
                       then Typ
                       else Data
         pure (PPrimVal (boundToFC fname x) x.val)
  <|> do x <- bounds $ decoratedSymbol fname "_"
         pure (PImplicit (boundToFC fname x))
  <|> do x <- bounds $ symbol "?"
         pure (PInfer (boundToFC fname x))
  <|> do x <- bounds $ holeName
         actH x.val -- record the hole name in the parser
         pure (PHole (boundToFC fname x) False x.val)
  <|> do x <- bounds $ decorate fname Data $ pragma "MkWorld"
         pure (PPrimVal (boundToFC fname x) WorldVal)
  <|> do x <- bounds $ decorate fname Typ  $ pragma "World"
         pure (PPrimVal (boundToFC fname x) $ PrT WorldType)
  <|> do x <- bounds $ decoratedPragma fname "search"
         pure (PSearch (boundToFC fname x) 50)

whereBlock : OriginDesc -> Int -> Rule (List PDecl)
whereBlock fname col
    = do decoratedKeyword fname "where"
         ds <- blockAfter col (topDecl fname)
         pure (collectDefs (concat ds))

-- Expect a keyword, but if we get anything else it's a fatal error
commitKeyword : OriginDesc -> IndentInfo -> String -> Rule ()
commitKeyword fname indents req
    = do mustContinue indents (Just req)
         decoratedKeyword fname req
          <|> the (Rule ()) (fatalError ("Expected '" ++ req ++ "'"))
         mustContinue indents Nothing

commitSymbol : OriginDesc -> String -> Rule ()
commitSymbol fname req
    = decoratedSymbol fname req
       <|> fatalError ("Expected '" ++ req ++ "'")

continueWithDecorated : OriginDesc -> IndentInfo -> String -> Rule ()
continueWithDecorated fname indents req
    = mustContinue indents (Just req) *> decoratedSymbol fname req


continueWith : IndentInfo -> String -> Rule ()
continueWith indents req
    = mustContinue indents (Just req) *> symbol req

iOperator : Rule OpStr
iOperator
    = OpSymbols <$> operator
  <|> Backticked <$> (symbol "`" *> name <* symbol "`")

data ArgType
    = UnnamedExpArg PTerm
    | UnnamedAutoArg PTerm
    | NamedArg Name PTerm
    | WithArg PTerm

argTerm : ArgType -> PTerm
argTerm (UnnamedExpArg t) = t
argTerm (UnnamedAutoArg t) = t
argTerm (NamedArg _ t) = t
argTerm (WithArg t) = t

export
debugString : OriginDesc -> Rule PTerm
debugString fname = do
  di <- bounds debugInfo
  pure $ PPrimVal (boundToFC fname di) $ Str $ case di.val of
    DebugLoc =>
      let bnds = di.bounds in
      joinBy ", "
      [ "File \{show fname}"
      , "line \{show (startLine bnds)}"
      , "characters \{show (startCol bnds)}\{
           ifThenElse (startLine bnds == endLine bnds)
            ("-\{show (endCol bnds)}")
            ""
        }"
      ]
    DebugFile => "\{show fname}"
    DebugLine => "\{show (startLine di.bounds)}"
    DebugCol => "\{show (startCol di.bounds)}"

totalityOpt : OriginDesc -> Rule TotalReq
totalityOpt fname
    = (decoratedKeyword fname "partial" $> PartialOK)
  <|> (decoratedKeyword fname "total" $> Total)
  <|> (decoratedKeyword fname "covering" $> CoveringOnly)

fnOpt : OriginDesc -> Rule PFnOpt
fnOpt fname
      = do x <- totalityOpt fname
           pure $ IFnOpt (Totality x)

mutual
  appExpr : ParseOpts -> OriginDesc -> IndentInfo -> Rule PTerm
  appExpr q fname indents
      = case_ fname indents
    <|> doBlock fname indents
    <|> lam fname indents
    <|> lazy fname indents
    <|> if_ fname indents
    <|> with_ fname indents
    <|> do b <- bounds (MkPair <$> simpleExpr fname indents <*> many (argExpr q fname indents))
           (f, args) <- pure b.val
           pure (applyExpImp (start b) (end b) f (concat args))
    <|> do b <- bounds (MkPair <$> bounds iOperator <*> expr pdef fname indents)
           (op, arg) <- pure b.val
           pure (PPrefixOp (boundToFC fname b) (boundToFC fname op) op.val arg)
    <|> fail "Expected 'case', 'if', 'do', application or operator expression"
    where
      applyExpImp : FilePos -> FilePos -> PTerm ->
                    List ArgType ->
                    PTerm
      applyExpImp start end f [] = f
      applyExpImp start end f (UnnamedExpArg exp :: args)
          = applyExpImp start end (PApp (MkFC fname start end) f exp) args
      applyExpImp start end f (UnnamedAutoArg imp :: args)
          = applyExpImp start end (PAutoApp (MkFC fname start end) f imp) args
      applyExpImp start end f (NamedArg n imp :: args)
          = let fc = MkFC fname start end in
            applyExpImp start end (PNamedApp fc f n imp) args
      applyExpImp start end f (WithArg exp :: args)
          = applyExpImp start end (PWithApp (MkFC fname start end) f exp) args

  argExpr : ParseOpts -> OriginDesc -> IndentInfo -> Rule (List ArgType)
  argExpr q fname indents
      = do continue indents
           arg <- simpleExpr fname indents
           the (EmptyRule _) $ case arg of
                PHole loc _ n => pure [UnnamedExpArg (PHole loc True n)]
                t => pure [UnnamedExpArg t]
    <|> do continue indents
           braceArgs fname indents
    <|> if withOK q
           then do continue indents
                   decoratedSymbol fname "|"
                   arg <- expr ({withOK := False} q) fname indents
                   pure [WithArg arg]
           else fail "| not allowed here"
    where
      underscore : FC -> ArgType
      underscore fc = NamedArg (UN Underscore) (PImplicit fc)

      braceArgs : OriginDesc -> IndentInfo -> Rule (List ArgType)
      braceArgs fname indents
        = do start <- bounds (decoratedSymbol fname "{")
             mustWork $ do
               list <- sepBy (decoratedSymbol fname ",")
                        $ do x <- bounds (UN . Basic <$> decoratedSimpleNamedArg fname)
                             let fc = boundToFC fname x
                             option (NamedArg x.val $ PRef fc x.val)
                              $ do tm <- decoratedSymbol fname "=" *> typeExpr pdef fname indents
                                   pure (NamedArg x.val tm)
               matchAny <- option [] (if isCons list then
                                         do decoratedSymbol fname ","
                                            x <- bounds (decoratedSymbol fname "_")
                                            pure [underscore (boundToFC fname x)]
                                      else fail "non-empty list required")
               end <- bounds (decoratedSymbol fname "}")
               matchAny <- do let fc = boundToFC fname (mergeBounds start end)
                              pure $ if isNil list
                                then [underscore fc]
                                else matchAny
               pure $ matchAny ++ list

        <|> do decoratedSymbol fname "@{"
               commit
               tm <- typeExpr pdef fname indents
               decoratedSymbol fname "}"
               pure [UnnamedAutoArg tm]

  with_ : OriginDesc -> IndentInfo -> Rule PTerm
  with_ fname indents
      = do b <- bounds (do decoratedKeyword fname "with"
                           commit
                           ns <- singleName <|> nameList
                           end <- location
                           rhs <- expr pdef fname indents
                           pure (ns, rhs))
           (ns, rhs) <- pure b.val
           pure (PWithUnambigNames (boundToFC fname b) ns rhs)
    where
      singleName : Rule (List (FC, Name))
      singleName = do
        n <- bounds name
        pure [(boundToFC fname n, n.val)]

      nameList : Rule (List (FC, Name))
      nameList = do
        decoratedSymbol fname "["
        commit
        ns <- sepBy1 (decoratedSymbol fname ",") (bounds name)
        decoratedSymbol fname "]"
        pure (map (\ n => (boundToFC fname n, n.val)) $ forget ns)

  -- The different kinds of operator bindings `x : ty` for typebind
  -- x := e and x : ty := e for autobind
  opBinderTypes : OriginDesc -> IndentInfo -> WithBounds PTerm -> Rule (OperatorLHSInfo PTerm)
  opBinderTypes fname indents boundName =
           do decoratedSymbol fname ":"
              ty <- typeExpr pdef fname indents
              decoratedSymbol fname ":="
              exp <- expr pdef fname indents
              pure (BindExplicitType boundName.val ty exp)
       <|> do decoratedSymbol fname ":="
              exp <- expr pdef fname indents
              pure (BindExpr boundName.val exp)
       <|> do decoratedSymbol fname ":"
              ty <- typeExpr pdef fname indents
              pure (BindType boundName.val ty)

  opBinder : OriginDesc -> IndentInfo -> Rule (OperatorLHSInfo PTerm)
  opBinder fname indents
      = do boundName <- bounds (expr plhs fname indents)
           opBinderTypes fname indents boundName

  autobindOp : ParseOpts -> OriginDesc -> IndentInfo -> Rule PTerm
  autobindOp q fname indents
      = do binder <- bounds $ parens fname (opBinder fname indents)
           continue indents
           op <- bounds iOperator
           commit
           e <- bounds (expr q fname indents)
           pure (POp (boundToFC fname $ mergeBounds binder e)
                     (boundToFC fname op)
                     binder.val
                     op.val
                     e.val)

  opExprBase : ParseOpts -> OriginDesc -> IndentInfo -> Rule PTerm
  opExprBase q fname indents
      = do l <- bounds (appExpr q fname indents)
           (if eqOK q
               then do r <- bounds (continue indents
                                *> decoratedSymbol fname "="
                                *> opExprBase q fname indents)
                       pure $
                         let fc = boundToFC fname (mergeBounds l r)
                             opFC = virtualiseFC fc -- already been highlighted: we don't care
                         in POp fc opFC (NoBinder l.val) (OpSymbols $ UN $ Basic "=") r.val
               else fail "= not allowed")
             <|>
             (do b <- bounds $ do
                        continue indents
                        op <- bounds iOperator
                        e <- case op.val of
                               OpSymbols (UN (Basic "$")) => typeExpr q fname indents
                               _ => expr q fname indents
                        pure (op, e)
                 (op, r) <- pure b.val
                 let fc = boundToFC fname (mergeBounds l b)
                 let opFC = boundToFC fname op
                 pure (POp fc opFC (NoBinder l.val) op.val r))
               <|> pure l.val

  opExpr : ParseOpts -> OriginDesc -> IndentInfo -> Rule PTerm
  opExpr q fname indents = autobindOp q fname indents
                       <|> opExprBase q fname indents

  dpairType : OriginDesc -> WithBounds t -> IndentInfo -> Rule PTerm
  dpairType fname start indents
      = do loc <- bounds (do x <- UN . Basic <$> decoratedSimpleBinderName fname
                             decoratedSymbol fname ":"
                             ty <- typeExpr pdef fname indents
                             pure (x, ty))
           (x, ty) <- pure loc.val
           op <- bounds (symbol "**")
           rest <- bounds (nestedDpair fname loc indents <|> typeExpr pdef fname indents)
           pure (PDPair (boundToFC fname (mergeBounds start rest))
                        (boundToFC fname op)
                        (PRef (boundToFC fname loc) x)
                        ty
                        rest.val)

  nestedDpair : OriginDesc -> WithBounds t -> IndentInfo -> Rule PTerm
  nestedDpair fname start indents
      = dpairType fname start indents
    <|> do l <- expr pdef fname indents
           loc <- bounds (symbol "**")
           rest <- bounds (nestedDpair fname loc indents <|> expr pdef fname indents)
           pure (PDPair (boundToFC fname (mergeBounds start rest))
                        (boundToFC fname loc)
                        l
                        (PImplicit (boundToFC fname (mergeBounds start rest)))
                        rest.val)

  bracketedExpr : OriginDesc -> WithBounds t -> IndentInfo -> Rule PTerm
  bracketedExpr fname s indents
      -- left section. This may also be a prefix operator, but we'll sort
      -- that out when desugaring: if the operator is infix, treat it as a
      -- section otherwise treat it as prefix
      = do b <- bounds (do op <- bounds iOperator
                           e <- expr pdef fname indents
                           continueWithDecorated fname indents ")"
                           pure (op, e))
           (op, e) <- pure b.val
           actD (toNonEmptyFC $ boundToFC fname s, Keyword, Nothing)
           let fc = boundToFC fname (mergeBounds s b)
           let opFC = boundToFC fname op
           pure (PSectionL fc opFC op.val e)
    <|> do  -- (.y.z)  -- section of projection (chain)
           b <- bounds $ forget <$> some (bounds postfixProj)
           decoratedSymbol fname ")"
           actD (toNonEmptyFC $ boundToFC fname s, Keyword, Nothing)
           let projs = map (\ proj => (boundToFC fname proj, proj.val)) b.val
           pure $ PPostfixAppPartial (boundToFC fname b) projs
      -- unit type/value
    <|> do b <- bounds (continueWith indents ")")
           pure (PUnit (boundToFC fname (mergeBounds s b)))
      -- dependent pairs with type annotation (so, the type form)
    <|> do dpairType fname s indents <* (decorate fname Typ $ symbol ")")
                                     <* actD (toNonEmptyFC $ boundToFC fname s, Typ, Nothing)
    <|> do e <- bounds (typeExpr pdef fname indents)
           -- dependent pairs with no type annotation
           (do loc <- bounds (symbol "**")
               rest <- bounds ((nestedDpair fname loc indents <|> expr pdef fname indents) <* symbol ")")
               pure (PDPair (boundToFC fname (mergeBounds s rest))
                            (boundToFC fname loc)
                            e.val
                            (PImplicit (boundToFC fname (mergeBounds s rest)))
                            rest.val)) <|>
             -- right sections
             ((do op <- bounds (bounds iOperator <* decoratedSymbol fname ")")
                  actD (toNonEmptyFC $ boundToFC fname s, Keyword, Nothing)
                  let fc = boundToFC fname (mergeBounds s op)
                  let opFC = boundToFC fname op.val
                  pure (PSectionR fc opFC e.val op.val.val)
               <|>
              -- all the other bracketed expressions
              tuple fname s indents e.val))
    <|> do here <- location
           let fc = MkFC fname here here
           let var = PRef fc (MN "__leftTupleSection" 0)
           ts <- bounds (nonEmptyTuple fname s indents var)
           pure (PLam fc top Explicit var (PInfer fc) ts.val)

  getInitRange : List (WithBounds PTerm) -> EmptyRule (PTerm, Maybe PTerm)
  getInitRange [x] = pure (x.val, Nothing)
  getInitRange [x,y] = pure (x.val, Just y.val)
  getInitRange _ = fatalError "Invalid list range syntax"

  listRange : OriginDesc -> WithBounds t -> IndentInfo -> List (WithBounds PTerm) -> Rule PTerm
  listRange fname s indents xs
      = do b <- bounds (decoratedSymbol fname "]")
           let fc = boundToFC fname (mergeBounds s b)
           rstate <- getInitRange xs
           decorateKeywords fname xs
           pure (PRangeStream fc (fst rstate) (snd rstate))
    <|> do y <- bounds (expr pdef fname indents <* decoratedSymbol fname "]")
           let fc = boundToFC fname (mergeBounds s y)
           rstate <- getInitRange xs
           decorateKeywords fname xs
           pure (PRange fc (fst rstate) (snd rstate) y.val)

  listExpr : OriginDesc -> WithBounds () -> IndentInfo -> Rule PTerm
  listExpr fname s indents
      = do b <- bounds (do ret <- expr pnowith fname indents
                           decoratedSymbol fname "|"
                           conds <- sepBy1 (decoratedSymbol fname ",") (doAct fname indents)
                           decoratedSymbol fname "]"
                           pure (ret, conds))
           (ret, conds) <- pure b.val
           pure (PComprehension (boundToFC fname (mergeBounds s b)) ret (concat conds))
    <|> do xs <- option [] $ do
                     hd <- expr pdef fname indents
                     tl <- many $ do b <- bounds (symbol ",")
                                     x <- mustWork $ expr pdef fname indents
                                     pure (x <$ b)
                     pure ((hd <$ s) :: tl)
           (do decoratedSymbol fname ".."
               listRange fname s indents xs)
             <|> (do b <- bounds (symbol "]")
                     pure $
                       let fc = boundToFC fname (mergeBounds s b)
                           nilFC = if null xs then fc else boundToFC fname b
                       in PList fc nilFC (cast (map (\ t => (boundToFC fname t, t.val)) xs)))

  snocListExpr : OriginDesc -> WithBounds () -> IndentInfo -> Rule PTerm
  snocListExpr fname s indents
      = {- TODO: comprehension -}
        do mHeadTail <- optional $ do
             hd <- many $ do x <- expr pdef fname indents
                             b <- bounds (symbol ",")
                             pure (x <$ b)
             tl <- expr pdef fname indents
             pure (hd, tl)
           {- TODO: reverse ranges -}
           b <- bounds (symbol "]")
           pure $
             let xs : SnocList (WithBounds PTerm)
                    = case mHeadTail of
                        Nothing      => [<]
                        Just (hd,tl) => ([<] <>< hd) :< (tl <$ b)
                 fc = boundToFC fname (mergeBounds s b)
                 nilFC = ifThenElse (null xs) fc (boundToFC fname s)
             in PSnocList fc nilFC (map (\ t => (boundToFC fname t, t.val)) xs) --)

  nonEmptyTuple : OriginDesc -> WithBounds t -> IndentInfo -> PTerm -> Rule PTerm
  nonEmptyTuple fname s indents e
      = do vals <- some $ do b <- bounds (symbol ",")
                             exp <- optional (typeExpr pdef fname indents)
                             pure (boundToFC fname b, exp)
           end <- continueWithDecorated fname indents ")"
           actD (toNonEmptyFC (boundToFC fname s), Keyword, Nothing)
           pure $ let (start ::: rest) = vals in
                  buildOutput (fst start) (mergePairs 0 start rest)
    where

      lams : List (FC, PTerm) -> PTerm -> PTerm
      lams [] e = e
      lams ((fc, var) :: vars) e
        = let vfc = virtualiseFC fc in
          PLam vfc top Explicit var (PInfer vfc) $ lams vars e

      buildOutput : FC -> (List (FC, PTerm), PTerm) -> PTerm
      buildOutput fc (vars, scope) = lams vars $ PPair fc e scope

      optionalPair : Int ->
                     (FC, Maybe PTerm) -> (Int, (List (FC, PTerm), PTerm))
      optionalPair i (fc, Just e)  = (i, ([], e))
      optionalPair i (fc, Nothing) =
        let var = PRef fc (MN "__infixTupleSection" i) in
        (i+1, ([(fc, var)], var))

      mergePairs : Int -> (FC, Maybe PTerm) ->
                   List (FC, Maybe PTerm) -> (List (FC, PTerm), PTerm)
      mergePairs i hd [] = snd (optionalPair i hd)
      mergePairs i hd (exp :: rest)
          = let (j, (var, t)) = optionalPair i hd in
            let (vars, ts)    = mergePairs j exp rest in
            (var ++ vars, PPair (fst exp) t ts)

  -- A pair, dependent pair, or just a single expression
  tuple : OriginDesc -> WithBounds t -> IndentInfo -> PTerm -> Rule PTerm
  tuple fname s indents e
     =   nonEmptyTuple fname s indents e
     <|> do end <- bounds (continueWithDecorated fname indents ")")
            actD (toNonEmptyFC $ boundToFC fname s, Keyword, Nothing)
            pure (PBracketed (boundToFC fname (mergeBounds s end)) e)

  simpleExpr : OriginDesc -> IndentInfo -> Rule PTerm
  simpleExpr fname indents
    = do  -- x.y.z
          b <- bounds (do root <- simplerExpr fname indents
                          projs <- many (bounds postfixProj)
                          pure (root, projs))
          (root, projs) <- pure b.val
          let projs = map (\ proj => (boundToFC fname proj, proj.val)) projs
          pure $ case projs of
            [] => root
            _  => PPostfixApp (boundToFC fname b) root projs
    <|> debugString fname
    <|> do b <- bounds (forget <$> some (bounds postfixProj))
           pure $ let projs = map (\ proj => (boundToFC fname proj, proj.val)) b.val in
                  PPostfixAppPartial (boundToFC fname b) projs

  simplerExpr : OriginDesc -> IndentInfo -> Rule PTerm
  simplerExpr fname indents
      = do b <- bounds (do x <- bounds (UN . Basic <$> decoratedSimpleBinderName fname)
                           decoratedSymbol fname "@"
                           commit
                           expr <- simpleExpr fname indents
                           pure (x, expr))
           (x, expr) <- pure b.val
           pure (PAs (boundToFC fname b) (boundToFC fname x) x.val expr)
    <|> do b <- bounds $ do
                  mns <- decoratedNamespacedSymbol fname "[|"
                  t   <- expr pdef fname indents
                  decoratedSymbol fname "|]"
                  pure (t, mns)
           pure (PIdiom (boundToFC fname b) (snd b.val) (fst b.val))
    <|> atom fname
    <|> record_ fname indents
    <|> singlelineStr pdef fname indents
    <|> multilineStr pdef fname indents
    <|> do b <- bounds $ do
                  decoratedSymbol fname ".("
                  commit
                  t <- typeExpr pdef fname indents
                  decoratedSymbol fname ")"
                  pure t
           pure (PDotted (boundToFC fname b) b.val)
    <|> do b <- bounds $ do
                  decoratedSymbol fname "`("
                  t <- typeExpr pdef fname indents
                  decoratedSymbol fname ")"
                  pure t
           pure (PQuote (boundToFC fname b) b.val)
    <|> do b <- bounds $ do
                  decoratedSymbol fname "`{"
                  t <- name
                  decoratedSymbol fname "}"
                  pure t
           pure (PQuoteName (boundToFC fname b) b.val)
    <|> do b <- bounds $ do
                  decoratedSymbol fname "`["
                  ts <- nonEmptyBlock (topDecl fname)
                  decoratedSymbol fname "]"
                  pure ts
           pure (PQuoteDecl (boundToFC fname b) (collectDefs (concat b.val)))
    <|> do b <- bounds (decoratedSymbol fname "~" *> simplerExpr fname indents)
           pure (PUnquote (boundToFC fname b) b.val)
    <|> do start <- bounds (symbol "(")
           bracketedExpr fname start indents
    <|> do start <- bounds (symbol "[<")
           snocListExpr fname start indents
    <|> do start <- bounds (symbol "[>" <|> symbol "[")
           listExpr fname start indents
    <|> do b <- bounds (decoratedSymbol fname "!" *> simpleExpr fname indents)
           pure (PBang (virtualiseFC $ boundToFC fname b) b.val)
    <|> do b <- bounds $ do decoratedPragma fname "logging"
                            topic <- optional (split (('.') ==) <$> simpleStr)
                            lvl   <- intLit
                            e     <- expr pdef fname indents
                            pure (MkPair (mkLogLevel' topic (integerToNat lvl)) e)
           (lvl, e) <- pure b.val
           pure (PUnifyLog (boundToFC fname b) lvl e)
    <|> withWarning "DEPRECATED: trailing lambda. Use a $ or parens"
        (lam fname indents)

  multiplicity : OriginDesc -> EmptyRule RigCount
  multiplicity fname
      = case !(optional $ decorate fname Keyword intLit) of
          (Just 0) => pure erased
          (Just 1) => pure linear
          Nothing => pure top
          _ => fail "Invalid multiplicity (must be 0 or 1)"

  pibindAll : OriginDesc -> PiInfo PTerm ->
              List (RigCount, WithBounds (Maybe Name), PTerm) ->
              PTerm -> PTerm
  pibindAll fname p [] scope = scope
  pibindAll fname p ((rig, n, ty) :: rest) scope
           = PPi (boundToFC fname n) rig p (n.val) ty (pibindAll fname p rest scope)

  bindList : OriginDesc -> IndentInfo ->
             Rule (List (RigCount, WithBounds PTerm, PTerm))
  bindList fname indents
      = forget <$> sepBy1 (decoratedSymbol fname ",")
                          (do rig <- multiplicity fname
                              pat <- bounds (simpleExpr fname indents)
                              ty <- option
                                       (PInfer (boundToFC fname pat))
                                       (decoratedSymbol fname ":" *> opExpr pdef fname indents)
                              pure (rig, pat, ty))

  pibindListName : OriginDesc -> IndentInfo ->
                   Rule (List (RigCount, WithBounds Name, PTerm))
  pibindListName fname indents
       = do rig <- multiplicity fname
            ns <- sepBy1 (decoratedSymbol fname ",")
                         (bounds $ UN <$> binderName)
            let ns = forget ns
            decorateBoundedNames fname Bound ns
            decoratedSymbol fname ":"
            ty <- typeExpr pdef fname indents
            atEnd indents
            pure (map (\n => (rig, n, ty)) ns)
    where
      -- _ gets treated specially here, it means "I don't care about the name"
      binderName : Rule UserName
      binderName = Basic <$> unqualifiedName
               <|> symbol "_" $> Underscore

  PiBindList : Type
  PiBindList = List (RigCount, WithBounds (Maybe Name), PTerm)

  pibindList : OriginDesc -> IndentInfo ->
               Rule PiBindList
  pibindList fname indents
    = do params <- pibindListName fname indents
         pure $ map (\(rig, n, ty) => (rig, map Just n, ty)) params

  bindSymbol : OriginDesc -> Rule (PiInfo PTerm)
  bindSymbol fname
      = (decoratedSymbol fname "->" $> Explicit)
    <|> (decoratedSymbol fname "=>" $> AutoImplicit)

  explicitPi : OriginDesc -> IndentInfo -> Rule PTerm
  explicitPi fname indents
      = do b <- bounds $ parens fname $ pibindList fname indents
           exp <- mustWorkBecause b.bounds "Cannot return a named argument"
                    $ bindSymbol fname
           scope <- mustWork $ typeExpr pdef fname indents
           pure (pibindAll fname exp b.val scope)

  autoImplicitPi : OriginDesc -> IndentInfo -> Rule PTerm
  autoImplicitPi fname indents
      = do b <- bounds $ do
                  decoratedSymbol fname "{"
                  decoratedKeyword fname "auto"
                  commit
                  binders <- pibindList fname indents
                  decoratedSymbol fname "}"
                  pure binders
           mustWorkBecause b.bounds "Cannot return an auto implicit argument"
             $ decoratedSymbol fname "->"
           scope <- mustWork $ typeExpr pdef fname indents
           pure (pibindAll fname AutoImplicit b.val scope)

  defaultImplicitPi : OriginDesc -> IndentInfo -> Rule PTerm
  defaultImplicitPi fname indents
      = do b <- bounds $ do
                  decoratedSymbol fname "{"
                  decoratedKeyword fname "default"
                  commit
                  t <- simpleExpr fname indents
                  binders <- pibindList fname indents
                  decoratedSymbol fname "}"
                  pure (t, binders)
           mustWorkBecause b.bounds "Cannot return a default implicit argument"
             $ decoratedSymbol fname "->"
           scope <- mustWork $ typeExpr pdef fname indents
           pure $ let (t, binders) = b.val in
                  pibindAll fname (DefImplicit t) binders scope

  forall_ : OriginDesc -> IndentInfo -> Rule PTerm
  forall_ fname indents
      = do b <- bounds $ do
                  decoratedKeyword fname "forall"
                  commit
                  ns <- sepBy1 (decoratedSymbol fname ",")
                               (bounds (decoratedSimpleBinderName fname))
                  pure $ map (\n => ( erased {a=RigCount}
                                    , map (Just . UN . Basic) n
                                    , PImplicit (boundToFC fname n))
                             ) (forget ns)
           b' <- bounds peek
           mustWorkBecause b'.bounds "Expected ',' or '.'"
             $ decoratedSymbol fname "."
           scope <- mustWork $ typeExpr pdef fname indents
           pure (pibindAll fname Implicit b.val scope)

  implicitPi : OriginDesc -> IndentInfo -> Rule PTerm
  implicitPi fname indents
      = do b <- bounds $ do
                  decoratedSymbol fname "{"
                  binders <- pibindList fname indents
                  decoratedSymbol fname "}"
                  pure binders
           mustWorkBecause b.bounds "Cannot return an implicit argument"
            $ decoratedSymbol fname "->"
           scope <- mustWork $ typeExpr pdef fname indents
           pure (pibindAll fname Implicit b.val scope)

  lam : OriginDesc -> IndentInfo -> Rule PTerm
  lam fname indents
      = do decoratedSymbol fname "\\"
           commit
           switch <- optional (bounds $ decoratedKeyword fname "case")
           case switch of
             Nothing => continueLamImpossible <|> continueLam
             Just r  => continueLamCase r

     where
       continueLamImpossible : Rule PTerm
       continueLamImpossible = do
           lhs <- bounds (opExpr plhs fname indents)
           end <- bounds (decoratedKeyword fname "impossible")
           pure (
             let fc = boundToFC fname (mergeBounds lhs end)
                 alt = (MkImpossible fc lhs.val)
                 fcCase = boundToFC fname lhs
                 n = MN "lcase" 0 in
             (PLam fcCase top Explicit (PRef fcCase n) (PInfer fcCase) $
                 PCase (virtualiseFC fc) [] (PRef fcCase n) [alt]))

       bindAll : List (RigCount, WithBounds PTerm, PTerm) -> PTerm -> PTerm
       bindAll [] scope = scope
       bindAll ((rig, pat, ty) :: rest) scope
           = PLam (boundToFC fname pat) rig Explicit pat.val ty
                  (bindAll rest scope)

       continueLam : Rule PTerm
       continueLam = do
           binders <- bindList fname indents
           commitSymbol fname "=>"
           mustContinue indents Nothing
           scope <- typeExpr pdef fname indents
           pure (bindAll binders scope)

       continueLamCase : WithBounds () -> Rule PTerm
       continueLamCase endCase = do
           b <- bounds (forget <$> nonEmptyBlock (caseAlt fname))
           pure
            (let fc = boundToFC fname b
                 fcCase = virtualiseFC $ boundToFC fname endCase
                 n = MN "lcase" 0 in
              PLam fcCase top Explicit (PRef fcCase n) (PInfer fcCase) $
                PCase (virtualiseFC fc) [] (PRef fcCase n) b.val)

  letBlock : OriginDesc -> IndentInfo -> Rule (WithBounds (Either LetBinder LetDecl))
  letBlock fname indents = bounds (letBinder <||> letDecl) where

    letBinder : Rule LetBinder
    letBinder = do s <- bounds (MkPair <$> multiplicity fname <*> expr plhs fname indents)
                   (rig, pat) <- pure s.val
                   ty <- option (PImplicit (virtualiseFC $ boundToFC fname s))
                                (decoratedSymbol fname ":" *> typeExpr (pnoeq pdef) fname indents)
                   (decoratedSymbol fname "=" <|> decoratedSymbol fname ":=")
                   val <- typeExpr pnowith fname indents
                   alts <- block (patAlt fname)
                   pure (MkLetBinder rig pat ty val alts)

    letDecl : Rule LetDecl
    letDecl = collectDefs . concat <$> nonEmptyBlock (try . topDecl fname)

  let_ : OriginDesc -> IndentInfo -> Rule PTerm
  let_ fname indents
      = do decoratedKeyword fname "let"
           commit
           res <- nonEmptyBlock (letBlock fname)
           commitKeyword fname indents "in"
           scope <- typeExpr pdef fname indents
           pure (mkLets fname res scope)

  case_ : OriginDesc -> IndentInfo -> Rule PTerm
  case_ fname indents
      = do opts <- many (fnDirectOpt fname)
           b <- bounds (do decoratedKeyword fname "case"
                           scr <- expr pdef fname indents
                           mustWork (commitKeyword fname indents "of")
                           alts <- block (caseAlt fname)
                           pure (scr, alts))
           (scr, alts) <- pure b.val
           pure (PCase (virtualiseFC $ boundToFC fname b) opts scr alts)


  caseAlt : OriginDesc -> IndentInfo -> Rule PClause
  caseAlt fname indents
      = do lhs <- bounds (opExpr plhs fname indents)
           caseRHS fname lhs indents lhs.val

  caseRHS : OriginDesc -> WithBounds t -> IndentInfo -> PTerm -> Rule PClause
  caseRHS fname start indents lhs
      = do rhs <- bounds $ do
                    decoratedSymbol fname "=>"
                    mustContinue indents Nothing
                    typeExpr pdef fname indents
           atEnd indents
           let fc = boundToFC fname (mergeBounds start rhs)
           pure (MkPatClause fc lhs rhs.val [])
    <|> do end <- bounds (decoratedKeyword fname "impossible")
           atEnd indents
           pure (MkImpossible (boundToFC fname (mergeBounds start end)) lhs)
    <|> fatalError ("Expected '=>' or 'impossible'")

  if_ : OriginDesc -> IndentInfo -> Rule PTerm
  if_ fname indents
      = do b <- bounds (do decoratedKeyword fname "if"
                           commit
                           x <- expr pdef fname indents
                           commitKeyword fname indents "then"
                           t <- typeExpr pdef fname indents
                           commitKeyword fname indents "else"
                           e <- typeExpr pdef fname indents
                           pure (x, t, e))
           mustWork $ atEnd indents
           (x, t, e) <- pure b.val
           pure (PIfThenElse (boundToFC fname b) x t e)

  record_ : OriginDesc -> IndentInfo -> Rule PTerm
  record_ fname indents
      = do
           b <- (
               withWarning oldSyntaxWarning (
                 bounds (do
                   decoratedKeyword fname "record"
                   commit
                   body True
                 ))
             <|>
               bounds (body False))
           pure (PUpdate (boundToFC fname b) b.val)
    where
      oldSyntaxWarning : String
      oldSyntaxWarning = unlines
        [ "DEPRECATED: old record update syntax."
        , #"  Use "{ f := v } p" instead of "record { f = v } p""#
        , #"  and "{ f $= v } p" instead of "record { f $= v } p""#
        ]

      body : Bool -> Rule (List PFieldUpdate)
      body kw = do
        decoratedSymbol fname "{"
        commit
        fs <- sepBy1 (decoratedSymbol fname ",") (field kw fname indents)
        decoratedSymbol fname "}"
        pure $ forget fs

  field : Bool -> OriginDesc -> IndentInfo -> Rule PFieldUpdate
  field kw fname indents
      = do path <- map fieldName <$> [| decorate fname Function name :: many recFieldCompat |]
           upd <- (ifThenElse kw (decoratedSymbol fname "=") (decoratedSymbol fname ":=") $> PSetField)
                      <|>
                  (decoratedSymbol fname "$=" $> PSetFieldApp)
           val <- typeExpr plhs fname indents
           pure (upd path val)
    where
      fieldName : Name -> String
      fieldName (UN (Basic s)) = s
      fieldName (UN (Field s)) = s
      fieldName _ = "_impossible"

      -- this allows the dotted syntax .field
      -- but also the arrowed syntax ->field for compatibility with Idris 1
      recFieldCompat : Rule Name
      recFieldCompat = decorate fname Function postfixProj
                  <|> (decoratedSymbol fname "->"
                       *> decorate fname Function name)

  rewrite_ : OriginDesc -> IndentInfo -> Rule PTerm
  rewrite_ fname indents
      = do b <- bounds (do decoratedKeyword fname "rewrite"
                           rule <- expr pdef fname indents
                           commitKeyword fname indents "in"
                           tm <- typeExpr pdef fname indents
                           pure (rule, tm))
           (rule, tm) <- pure b.val
           pure (PRewrite (boundToFC fname b) rule tm)

  doBlock : OriginDesc -> IndentInfo -> Rule PTerm
  doBlock fname indents
      = do b <- bounds $ decoratedKeyword fname "do" *> block (doAct fname)
           commit
           pure (PDoBlock (virtualiseFC $ boundToFC fname b) Nothing (concat b.val))
    <|> do nsdo <- bounds namespacedIdent
           -- TODO: need to attach metadata correctly here
           the (EmptyRule PTerm) $ case nsdo.val of
                (ns, "do") =>
                   do commit
                      actions <- Core.bounds (block (doAct fname))
                      let fc = virtualiseFC $
                               boundToFC fname (mergeBounds nsdo actions)
                      pure (PDoBlock fc ns (concat actions.val))
                _ => fail "Not a namespaced 'do'"

  validPatternVar : Name -> EmptyRule ()
  validPatternVar (UN Underscore) = pure ()
  validPatternVar (UN (Basic n))
      = unless (lowerFirst n) $
          fail "Not a pattern variable"
  validPatternVar _ = fail "Not a pattern variable"

  doAct : OriginDesc -> IndentInfo -> Rule (List PDo)
  doAct fname indents
      = do b <- bounds (do rig <- multiplicity fname
                           n <- bounds (name <|> UN Underscore <$ symbol "_")
                           -- If the name doesn't begin with a lower case letter, we should
                           -- treat this as a pattern, so fail
                           validPatternVar n.val
                           ty <- optional (decoratedSymbol fname ":" *> typeExpr (pnoeq pdef) fname indents)
                           decoratedSymbol fname "<-"
                           val <- expr pdef fname indents
                           pure (n, rig, ty, val))
           atEnd indents
           let (n, rig, ty, val) = b.val
           pure [DoBind (boundToFC fname b) (boundToFC fname n) n.val rig ty val]
    <|> do decoratedKeyword fname "let"
           commit
           res <- nonEmptyBlock (letBlock fname)
           do b <- bounds (decoratedKeyword fname "in")
              fatalLoc {c = True} b.bounds "Let-in not supported in do block. Did you mean (let ... in ...)?"
             <|>
           do atEnd indents
              pure (mkDoLets fname res)
    <|> do b <- bounds (decoratedKeyword fname "rewrite" *> expr pdef fname indents)
           atEnd indents
           pure [DoRewrite (boundToFC fname b) b.val]
    <|> do e <- bounds (expr plhs fname indents)
           (atEnd indents $> [DoExp (virtualiseFC $ boundToFC fname e) e.val])
             <|> (do ty <- optional (decoratedSymbol fname ":" *> typeExpr (pnoeq pdef) fname indents)
                     b <- bounds $ decoratedSymbol fname "<-" *> [| (expr pnowith fname indents, block (patAlt fname)) |]
                     atEnd indents
                     let (v, alts) = b.val
                     let fc = virtualiseFC $ boundToFC fname (mergeBounds e b)
                     pure [DoBindPat fc e.val ty v alts])

  patAlt : OriginDesc -> IndentInfo -> Rule PClause
  patAlt fname indents
      = do decoratedSymbol fname "|"
           caseAlt fname indents

  lazy : OriginDesc -> IndentInfo -> Rule PTerm
  lazy fname indents
      = do tm <- bounds (decorate fname Typ (exactIdent "Lazy")
                         *> simpleExpr fname indents
                         <* mustFailBecause "Lazy only takes one argument" (continue indents >> simpleExpr fname indents))
           pure (PDelayed (boundToFC fname tm) LLazy tm.val)
    <|> do tm <- bounds (decorate fname Typ (exactIdent "Inf")
                         *> simpleExpr fname indents
                         <* mustFailBecause "Inf only takes one argument" (continue indents >> simpleExpr fname indents))
           pure (PDelayed (boundToFC fname tm) LInf tm.val)
    <|> do tm <- bounds (decorate fname Data (exactIdent "Delay")
                         *> simpleExpr fname indents
                         <* mustFailBecause "Delay only takes one argument" (continue indents >> simpleExpr fname indents))
           pure (PDelay (boundToFC fname tm) tm.val)
    <|> do tm <- bounds (decorate fname Data (exactIdent "Force")
                         *> simpleExpr fname indents
                         <* mustFailBecause "Force only takes one argument" (continue indents >> simpleExpr fname indents))
           pure (PForce (boundToFC fname tm) tm.val)

  binder : OriginDesc -> IndentInfo -> Rule PTerm
  binder fname indents
      = autoImplicitPi fname indents
    <|> defaultImplicitPi fname indents
    <|> forall_ fname indents
    <|> implicitPi fname indents
    <|> autobindOp pdef fname indents
    <|> explicitPi fname indents
    <|> lam fname indents

  typeExpr : ParseOpts -> OriginDesc -> IndentInfo -> Rule PTerm
  typeExpr q fname indents
      = binder fname indents
    <|> ((bounds $ do
            arg <- expr q fname indents
            mscope <- optional $ do
                continue indents
                bd <- bindSymbol fname
                scope <- mustWork $ typeExpr q fname indents
                pure (bd, scope)
            pure (arg, mscope))
        <&> \arg_mscope =>
            let fc = boundToFC fname arg_mscope
                (arg, mscope) = arg_mscope.val
             in mkPi fc arg mscope)

    where
      mkPi : FC -> PTerm -> Maybe (PiInfo PTerm, PTerm) -> PTerm
      mkPi _ arg Nothing = arg
      mkPi fc arg (Just (exp, a))
        = PPi fc top exp Nothing arg a

  export
  expr : ParseOpts -> OriginDesc -> IndentInfo -> Rule PTerm
  expr q fname indents
       = let_ fname indents
     <|> rewrite_ fname indents
     <|> do b <- bounds $
                   do decoratedPragma fname "runElab"
                      expr pdef fname indents
            pure (PRunElab (boundToFC fname b) b.val)
     <|> opExpr q fname indents

  interpBlock : ParseOpts -> OriginDesc -> IndentInfo -> Rule PTerm
  interpBlock q fname idents = interpBegin *> (mustWork $ expr q fname idents) <* interpEnd

  export
  singlelineStr : ParseOpts -> OriginDesc -> IndentInfo -> Rule PTerm
  singlelineStr q fname idents
      = decorate fname Data $
        do b <- bounds $ do begin <- bounds strBegin
                            commit
                            xs <- many $ bounds $ (interpBlock q fname idents) <||> strLitLines
                            pstrs <- case traverse toPStr xs of
                                          Left err => fatalLoc begin.bounds err
                                          Right pstrs => pure $ pstrs
                            strEnd
                            pure (begin.val, pstrs)
           pure $ let (hashtag, str) = b.val in
                      PString (boundToFC fname b) hashtag str
    where
      toPStr : (WithBounds $ Either PTerm (List1 String)) -> Either String PStr
      toPStr x = case x.val of
                      Right (str:::[]) => Right $ StrLiteral (boundToFC fname x) str
                      Right (_:::strs) => Left "Multi-line string is expected to begin with \"\"\""
                      Left tm => Right $ StrInterp (boundToFC fname x) tm

  export
  multilineStr : ParseOpts -> OriginDesc -> IndentInfo -> Rule PTerm
  multilineStr q fname idents
      = decorate fname Data $
        do b <- bounds $ do hashtag <- multilineBegin
                            commit
                            xs <- many $ bounds $ (interpBlock q fname idents) <||> strLitLines
                            endloc <- location
                            strEnd
                            pure (hashtag, endloc, toLines xs [<] [<])
           pure $ let (hashtag, (_, col), xs) = b.val in
                      PMultiline (boundToFC fname b) hashtag (fromInteger $ cast col) xs
    where
      toLines : List (WithBounds $ Either PTerm (List1 String)) ->
                SnocList PStr -> SnocList (List PStr) -> List (List PStr)
      toLines [] line acc = acc <>> [line <>> []]
      toLines (x::xs) line acc = case x.val of
        Left tm =>
          toLines xs (line :< StrInterp (boundToFC fname x) tm) acc
        Right (str:::[]) =>
          toLines xs (line :< StrLiteral (boundToFC fname x) str) acc
        Right (str:::strs@(_::_)) =>
          let fc = boundToFC fname x in
          toLines xs [< StrLiteral fc (last strs)]
            $ acc :< (line <>> [StrLiteral fc str])
            <>< map (\str => [StrLiteral fc str]) (init strs)

  fnDirectOpt : OriginDesc -> Rule PFnOpt
  fnDirectOpt fname
      = do decoratedPragma fname "hint"
           pure $ IFnOpt (Hint True)
    <|> do decoratedPragma fname "globalhint"
           pure $ IFnOpt (GlobalHint False)
    <|> do decoratedPragma fname "defaulthint"
           pure $ IFnOpt (GlobalHint True)
    <|> do decoratedPragma fname "inline"
           commit
           pure $ IFnOpt Inline
    <|> do decoratedPragma fname "unsafe"
           commit
           pure $ IFnOpt Unsafe
    <|> do decoratedPragma fname "noinline"
           commit
           pure $ IFnOpt NoInline
    <|> do decoratedPragma fname "deprecate"
           commit
           pure $ IFnOpt Deprecate
    <|> do decoratedPragma fname "tcinline"
           commit
           pure $ IFnOpt TCInline
    <|> do decoratedPragma fname "extern"
           pure $ IFnOpt ExternFn
    <|> do decoratedPragma fname "macro"
           pure $ IFnOpt Macro
    <|> do decoratedPragma fname "spec"
           ns <- sepBy (decoratedSymbol fname ",") name
           pure $ IFnOpt (SpecArgs ns)
    <|> do decoratedPragma fname "foreign"
           cs <- block (expr pdef fname)
           pure $ PForeign cs
    <|> do (decoratedPragma fname "export"
            <|> withWarning noMangleWarning
                (decoratedPragma fname "nomangle"))
           cs <- block (expr pdef fname)
           pure $ PForeignExport cs
    where
      noMangleWarning : String
      noMangleWarning = """
      DEPRECATED: "%nomangle".
        Use "%export" instead
      """


visOption : OriginDesc ->  Rule Visibility
visOption fname
    = (decoratedKeyword fname "public" *> decoratedKeyword fname "export" $> Public)
    -- If "public export" failed then we try to parse just "public" and emit an error message saying
    -- the user should use "public export"
  <|> (bounds (decoratedKeyword fname "public") >>= \x : WithBounds ()
    => the (Rule Visibility) (fatalLoc x.bounds
           #""public" keyword by itself is not an export modifier, did you mean "public export"?"#))
  <|> (decoratedKeyword fname "export" $> Export)
  <|> (decoratedKeyword fname "private" $> Private)


visibility : OriginDesc -> EmptyRule (WithDefault Visibility Private)
visibility fname
    = (specified <$> visOption fname)
  <|> pure defaulted

exportVisibility : OriginDesc -> EmptyRule (WithDefault Visibility Export)
exportVisibility fname
    = (specified <$> visOption fname)
  <|> pure defaulted

tyDecls : Rule Name -> String -> OriginDesc -> IndentInfo -> Rule (List1 PTypeDecl)
tyDecls declName predoc fname indents
    = do bs <- do docns <- sepBy1 (decoratedSymbol fname ",")
                                  [| (optDocumentation fname, bounds declName) |]
                  b <- bounds $ decoratedSymbol fname ":"
                  mustWorkBecause b.bounds "Expected a type declaration" $ do
                    ty  <- typeExpr pdef fname indents
                    pure $ map (\(doc, n) => (doc, n.val, boundToFC fname n, ty)) docns
         atEnd indents
         pure $ map (\(doc, n, nFC, ty) => (MkPTy nFC nFC n (predoc ++ doc) ty))
                    bs

withFlags : OriginDesc -> EmptyRule (List WithFlag)
withFlags fname
    = (do decoratedPragma fname "syntactic"
          (Syntactic ::) <$> withFlags fname)
  <|> pure []


withProblem : OriginDesc -> Int -> IndentInfo -> Rule PWithProblem
withProblem fname col indents
  = do rig <- multiplicity fname
       start <- mustWork $ bounds (decoratedSymbol fname "(")
       wval <- bracketedExpr fname start indents
       prf <- optional (decoratedKeyword fname "proof"
              *> UN . Basic <$> decoratedSimpleBinderName fname)
       pure (MkPWithProblem rig wval prf)

mutual
  parseRHS : (withArgs : Nat) ->
             OriginDesc -> WithBounds t -> Int ->
             IndentInfo -> (lhs : (PTerm, List (FC, PTerm))) -> Rule PClause
  parseRHS withArgs fname start col indents lhs
       = do b <- bounds $ do
                   decoratedSymbol fname "="
                   mustWork $ do
                     continue indents
                     rhs <- typeExpr pdef fname indents
                     ws <- option [] $ whereBlock fname col
                     pure (rhs, ws)
            b' <- bounds peek
            mustWorkBecause b'.bounds "Not the end of a block entry, check indentation" $ atEnd indents
            (rhs, ws) <- pure b.val
            let fc = boundToFC fname (mergeBounds start b)
            pure (MkPatClause fc (uncurry applyWithArgs lhs) rhs ws)
     <|> do b <- bounds $ do
                   decoratedKeyword fname "with"
                   commit
                   flags <- withFlags fname
                   wps <- sepBy1 (decoratedSymbol fname "|") (withProblem fname col indents)
                   ws <- mustWork $ nonEmptyBlockAfter col
                                  $ clause (S (length wps.tail) + withArgs) (Just lhs) fname
                   pure (flags, wps, forget ws)
            (flags, wps, ws) <- pure b.val
            let fc = boundToFC fname (mergeBounds start b)
            pure (MkWithClause fc (uncurry applyWithArgs lhs) wps flags ws)
     <|> do end <- bounds (decoratedKeyword fname "impossible")
            atEnd indents
            pure $ let fc = boundToFC fname (mergeBounds start end) in
                   MkImpossible fc (uncurry applyWithArgs lhs)

  clause : (withArgs : Nat) ->
           IMaybe (isSucc withArgs) (PTerm, List (FC, PTerm)) ->
           OriginDesc -> IndentInfo -> Rule PClause
  clause withArgs mlhs fname indents
      = do b <- bounds (do col   <- column
                           lhsws <- clauseLHS fname indents mlhs
                           extra <- many parseWithArg
                           pure (col, mapSnd (++ extra) lhsws))
           let col = Builtin.fst b.val
           let lhs = Builtin.snd b.val
           let extra = Builtin.snd lhs
           -- Can't have the dependent 'if' here since we won't be able
           -- to infer the termination status of the rule
           ifThenElse (withArgs /= length extra)
              (fatalError $ "Wrong number of 'with' arguments:"
                         ++ " expected " ++ show withArgs
                         ++ " but got " ++ show (length extra))
              (parseRHS withArgs fname b col indents lhs)
    where

      clauseLHS : OriginDesc -> IndentInfo ->
                  IMaybe b (PTerm, List (FC, PTerm)) ->
                  Rule (PTerm, List (FC, PTerm))
      -- we aren't in a `with` so there is nothing to skip
      clauseLHS fname indent Nothing
        = (,[]) <$> opExpr plhs fname indents
      -- in a with clause, give a different meaning to a `_` lhs
      clauseLHS fname indent (Just lhs)
        = do e <- opExpr plhs fname indents
             pure $ case e of
               PImplicit fc =>
                 let vfc = virtualiseFC fc in
                 bimap (substFC vfc) (map (map $ substFC vfc)) lhs
               _ => (e, [])

      parseWithArg : Rule (FC, PTerm)
      parseWithArg
          = do decoratedSymbol fname "|"
               tm <- bounds (expr plhs fname indents)
               pure (boundToFC fname tm, tm.val)

mkTyConType : OriginDesc -> FC -> List (WithBounds Name) -> PTerm
mkTyConType fname fc [] = PType (virtualiseFC fc)
mkTyConType fname fc (x :: xs)
   = let bfc = boundToFC fname x in
     PPi bfc top Explicit Nothing (PType (virtualiseFC fc))
     $ mkTyConType fname fc xs

mkDataConType : FC -> PTerm -> List ArgType -> Maybe PTerm
mkDataConType fc ret [] = Just ret
mkDataConType fc ret (UnnamedExpArg x :: xs)
    = PPi fc top Explicit Nothing x <$> mkDataConType fc ret xs
mkDataConType fc ret (UnnamedAutoArg x :: xs)
    = PPi fc top AutoImplicit Nothing x <$> mkDataConType fc ret xs
mkDataConType _ _ _ -- with and named applications not allowed in simple ADTs
    = Nothing

simpleCon : OriginDesc -> PTerm -> IndentInfo -> Rule PTypeDecl
simpleCon fname ret indents
    = do b <- bounds (do cdoc   <- optDocumentation fname
                         cname  <- bounds $ decoratedDataConstructorName fname
                         params <- many (argExpr plhs fname indents)
                         pure (cdoc, cname.val, boundToFC fname cname, params))
         atEnd indents
         (cdoc, cname, cnameFC, params) <- pure b.val
         let cfc = boundToFC fname b
         fromMaybe (fatalError "Named arguments not allowed in ADT constructors")
                   (pure . MkPTy cfc cnameFC cname cdoc <$> mkDataConType cfc ret (concat params))

simpleData : OriginDesc -> WithBounds t ->
             WithBounds Name -> IndentInfo -> Rule PDataDecl
simpleData fname start tyName indents
    = do b <- bounds (do params <- many (bounds $ decorate fname Bound name)
                         tyend <- bounds (decoratedSymbol fname "=")
                         mustWork $ do
                           let tyfc = boundToFC fname (mergeBounds start tyend)
                           let tyCon = PRef (boundToFC fname tyName) tyName.val
                           let toPRef = \ t => PRef (boundToFC fname t) t.val
                           let conRetTy = papply tyfc tyCon (map toPRef params)
                           cons <- sepBy1 (decoratedSymbol fname "|") (simpleCon fname conRetTy indents)
                           pure (params, tyfc, forget cons))
         (params, tyfc, cons) <- pure b.val
         pure (MkPData (boundToFC fname (mergeBounds start b)) tyName.val
                       (Just (mkTyConType fname tyfc params)) [] cons)

dataOpt : OriginDesc -> Rule DataOpt
dataOpt fname
    = (decorate fname Keyword (exactIdent "noHints") $> NoHints)
  <|> (decorate fname Keyword (exactIdent "uniqueSearch") $> UniqueSearch)
  <|> (do decorate fname Keyword (exactIdent "search")
          SearchBy <$> forget <$> some (decorate fname Bound name))
  <|> (decorate fname Keyword (exactIdent "external") $> External)
  <|> (decorate fname Keyword (exactIdent "noNewtype") $> NoNewtype)

dataOpts : OriginDesc -> EmptyRule (List DataOpt)
dataOpts fname = option [] $ do
  decoratedSymbol fname "["
  opts <- sepBy1 (decoratedSymbol fname ",") (dataOpt fname)
  decoratedSymbol fname "]"
  pure (forget opts)

dataBody : OriginDesc -> Int -> WithBounds t -> Name -> IndentInfo -> Maybe PTerm ->
          EmptyRule PDataDecl
dataBody fname mincol start n indents ty
    = do ty <- maybe (fail "Telescope is not optional in forward declaration") pure ty
         atEndIndent indents
         pure (MkPLater (boundToFC fname start) n ty)
  <|> do b <- bounds (do (mustWork $ decoratedKeyword fname "where")
                         opts <- dataOpts fname
                         cs <- blockAfter mincol (tyDecls (mustWork $ decoratedDataConstructorName fname) "" fname)
                         pure (opts, concatMap forget cs))
         (opts, cs) <- pure b.val
         pure (MkPData (boundToFC fname (mergeBounds start b)) n ty opts cs)

gadtData : OriginDesc -> Int -> WithBounds t ->
           WithBounds Name -> IndentInfo -> EmptyRule PDataDecl
gadtData fname mincol start tyName indents
    = do ty <- optional $
                 do decoratedSymbol fname ":"
                    commit
                    typeExpr pdef fname indents
         dataBody fname mincol start tyName.val indents ty

dataDeclBody : OriginDesc -> IndentInfo -> Rule PDataDecl
dataDeclBody fname indents
    = do b <- bounds (do col <- column
                         decoratedKeyword fname "data"
                         n <- mustWork (bounds $ decoratedDataTypeName fname)
                         pure (col, n))
         (col, n) <- pure b.val
         simpleData fname b n indents <|> gadtData fname col b n indents

-- a data declaration can have a visibility and an optional totality (#1404)
dataVisOpt : OriginDesc -> EmptyRule (WithDefault Visibility Private, Maybe TotalReq)
dataVisOpt fname
    = do { vis <- visOption   fname ; mbtot <- optional (totalityOpt fname) ; pure (specified vis, mbtot) }
  <|> do { tot <- totalityOpt fname ; vis <- visibility fname ; pure (vis, Just tot) }
  <|> pure (defaulted, Nothing)

dataDecl : OriginDesc -> IndentInfo -> Rule PDecl
dataDecl fname indents
    = do b <- bounds (do doc         <- optDocumentation fname
                         (vis,mbTot) <- dataVisOpt fname
                         dat         <- dataDeclBody fname indents
                         pure (doc, vis, mbTot, dat))
         (doc, vis, mbTot, dat) <- pure b.val
         pure (PData (boundToFC fname b) doc vis mbTot dat)

stripBraces : String -> String
stripBraces str = pack (drop '{' (reverse (drop '}' (reverse (unpack str)))))
  where
    drop : Char -> List Char -> List Char
    drop c [] = []
    drop c (c' :: xs) = if c == c' then drop c xs else c' :: xs

onoff : Rule Bool
onoff
   = (exactIdent "on" $> True)
 <|> (exactIdent "off" $> False)
 <|> fail "expected 'on' or 'off'"

extension : Rule LangExt
extension
    = (exactIdent "ElabReflection" $> ElabReflection)
  <|> (exactIdent "Borrowing" $> Borrowing)
  <|> fail "expected either 'ElabReflection' or 'Borrowing'"

logLevel : OriginDesc -> Rule (Maybe LogLevel)
logLevel fname
  = (Nothing <$ decorate fname Keyword (exactIdent "off"))
    <|> do topic <- optional (split ('.' ==) <$> simpleStr)
           lvl <- intLit
           pure (Just (mkLogLevel' topic (fromInteger lvl)))
    <|> fail "expected a log level"

directive : OriginDesc -> IndentInfo -> Rule Directive
directive fname indents
    = do decoratedPragma fname "hide"
         n <- (fixityNS <|> (HideName <$> name))
         atEnd indents
         pure (Hide n)
  <|> do decoratedPragma fname "unhide"
         n <- name
         atEnd indents
         pure (Unhide n)
  <|> do decoratedPragma fname "foreign_impl"
         n <- name
         cs <- block (expr pdef fname)
         atEnd indents
         pure (ForeignImpl n cs)
--   <|> do pragma "hide_export"
--          n <- name
--          atEnd indents
--          pure (Hide True n)
  <|> do decoratedPragma fname "logging"
         lvl <- logLevel fname
         atEnd indents
         pure (Logging lvl)
  <|> do decoratedPragma fname "auto_lazy"
         b <- onoff
         atEnd indents
         pure (LazyOn b)
  <|> do decoratedPragma fname "unbound_implicits"
         b <- onoff
         atEnd indents
         pure (UnboundImplicits b)
  <|> do decoratedPragma fname "prefix_record_projections"
         b <- onoff
         atEnd indents
         pure (PrefixRecordProjections b)
  <|> do decoratedPragma fname "ambiguity_depth"
         lvl <- decorate fname Keyword $ intLit
         atEnd indents
         pure (AmbigDepth (fromInteger lvl))
  <|> do decoratedPragma fname "auto_implicit_depth"
         dpt <- decorate fname Keyword $ intLit
         atEnd indents
         pure (AutoImplicitDepth (fromInteger dpt))
  <|> do decoratedPragma fname "nf_metavar_threshold"
         dpt <- decorate fname Keyword $ intLit
         atEnd indents
         pure (NFMetavarThreshold (fromInteger dpt))
  <|> do decoratedPragma fname "search_timeout"
         t <- decorate fname Keyword $ intLit
         atEnd indents
         pure (SearchTimeout t)
  <|> do decoratedPragma fname "pair"
         ty <- name
         f <- name
         s <- name
         atEnd indents
         pure (PairNames ty f s)
  <|> do decoratedPragma fname "rewrite"
         eq <- name
         rw <- name
         atEnd indents
         pure (RewriteName eq rw)
  <|> do decoratedPragma fname "integerLit"
         n <- name
         atEnd indents
         pure (PrimInteger n)
  <|> do decoratedPragma fname "stringLit"
         n <- name
         atEnd indents
         pure (PrimString n)
  <|> do decoratedPragma fname "charLit"
         n <- name
         atEnd indents
         pure (PrimChar n)
  <|> do decoratedPragma fname "doubleLit"
         n <- name
         atEnd indents
         pure (PrimDouble n)
  <|> do decoratedPragma fname "TTImpLit"
         n <- name
         atEnd indents
         pure (PrimTTImp n)
  <|> do decoratedPragma fname "nameLit"
         n <- name
         atEnd indents
         pure (PrimName n)
  <|> do decoratedPragma fname "declsLit"
         n <- name
         atEnd indents
         pure (PrimDecls n)
  <|> do decoratedPragma fname "name"
         n <- name
         ns <- sepBy1 (decoratedSymbol fname ",")
                       (decoratedSimpleBinderName fname)
         atEnd indents
         pure (Names n (forget ns))
  <|> do decoratedPragma fname "start"
         e <- expr pdef fname indents
         atEnd indents
         pure (StartExpr e)
  <|> do decoratedPragma fname "allow_overloads"
         n <- name
         atEnd indents
         pure (Overloadable n)
  <|> do decoratedPragma fname "language"
         e <- mustWork extension
         atEnd indents
         pure (Extension e)
  <|> do decoratedPragma fname "default"
         tot <- totalityOpt fname
         atEnd indents
         pure (DefaultTotality tot)

fix : Rule Fixity
fix
    = (keyword "infixl" $> InfixL)
  <|> (keyword "infixr" $> InfixR)
  <|> (keyword "infix"  $> Infix)
  <|> (keyword "prefix" $> Prefix)

namespaceHead : OriginDesc -> Rule Namespace
namespaceHead fname
  = do decoratedKeyword fname "namespace"
       decorate fname Namespace $ mustWork namespaceId

namespaceDecl : OriginDesc -> IndentInfo -> Rule PDecl
namespaceDecl fname indents
    = do b <- bounds (do doc   <- optDocumentation fname
                         col   <- column
                         ns    <- namespaceHead fname
                         ds    <- blockAfter col (topDecl fname)
                         pure (doc, ns, ds))
         (doc, ns, ds) <- pure b.val
         pure (PNamespace (boundToFC fname b) ns (collectDefs $ concat ds))

transformDecl : OriginDesc -> IndentInfo -> Rule PDecl
transformDecl fname indents
    = do b <- bounds (do decoratedPragma fname "transform"
                         n <- simpleStr
                         lhs <- expr plhs fname indents
                         decoratedSymbol fname "="
                         rhs <- expr pnowith fname indents
                         pure (n, lhs, rhs))
         (n, lhs, rhs) <- pure b.val
         pure (PTransform (boundToFC fname b) n lhs rhs)

runElabDecl : OriginDesc -> IndentInfo -> Rule PDecl
runElabDecl fname indents
    = do tm <- bounds $ do
                    decoratedPragma fname "runElab"
                    expr pnowith fname indents
         pure (PRunElabDecl (boundToFC fname tm) tm.val)

failDecls : OriginDesc -> IndentInfo -> Rule PDecl
failDecls fname indents
    = do msgds <- bounds $ do
                    col <- column
                    decoratedKeyword fname "failing"
                    commit
                    msg <- optional (decorate fname Data simpleStr)
                    (msg,) <$> nonEmptyBlockAfter col (topDecl fname)
         pure $
           let (msg, ds) = msgds.val
               fc = boundToFC fname msgds
           in PFail fc msg (collectDefs (concat ds))

mutualDecls : OriginDesc -> IndentInfo -> Rule PDecl
mutualDecls fname indents
    = do ds <- bounds $ do
                    col <- column
                    decoratedKeyword fname "mutual"
                    commit
                    nonEmptyBlockAfter col (topDecl fname)
         pure (PMutual (boundToFC fname ds) (concat ds.val))

usingDecls : OriginDesc -> IndentInfo -> Rule PDecl
usingDecls fname indents
    = do b <- bounds $ do
                    col <- column
                    decoratedKeyword fname "using"
                    commit
                    decoratedSymbol fname "("
                    us <- sepBy (decoratedSymbol fname ",")
                                (do n <- optional $ do
                                               x <- unqualifiedName
                                               decoratedSymbol fname ":"
                                               pure (UN $ Basic x)
                                    ty <- typeExpr pdef fname indents
                                    pure (n, ty))
                    decoratedSymbol fname ")"
                    ds <- nonEmptyBlockAfter col (topDecl fname)
                    pure (us, ds)
         (us, ds) <- pure b.val
         pure (PUsing (boundToFC fname b) us (collectDefs (concat ds)))

builtinDecl : OriginDesc -> IndentInfo -> Rule PDecl
builtinDecl fname indents
    = do b <- bounds (do decoratedPragma fname "builtin"
                         commit
                         t <- builtinType
                         n <- name
                         pure (t, n))
         (t, n) <- pure b.val
         pure $ PBuiltin (boundToFC fname b) t n

visOpt : OriginDesc -> Rule (Either Visibility PFnOpt)
visOpt fname
    = do vis <- visOption fname
         pure (Left vis)
  <|> do tot <- fnOpt fname
         pure (Right tot)
  <|> do opt <- fnDirectOpt fname
         pure (Right opt)

getVisibility : Maybe Visibility -> List (Either Visibility PFnOpt) ->
                EmptyRule Visibility
getVisibility Nothing [] = pure Private
getVisibility (Just vis) [] = pure vis
getVisibility Nothing (Left x :: xs) = getVisibility (Just x) xs
getVisibility (Just vis) (Left x :: xs)
   = fatalError "Multiple visibility modifiers"
getVisibility v (_ :: xs) = getVisibility v xs

recordConstructor : OriginDesc -> Rule (String, Name)
recordConstructor fname
  = do doc <- optDocumentation fname
       decorate fname Keyword $ exactIdent "constructor"
       n <- mustWork $ decoratedDataConstructorName fname
       pure (doc, n)

autoImplicitField : OriginDesc -> IndentInfo -> Rule (PiInfo t)
autoImplicitField fname _ = AutoImplicit <$ decoratedKeyword fname "auto"

defImplicitField : OriginDesc -> IndentInfo -> Rule (PiInfo PTerm)
defImplicitField fname indents = do
  decoratedKeyword fname "default"
  commit
  t <- simpleExpr fname indents
  pure (DefImplicit t)

constraints : OriginDesc -> IndentInfo -> EmptyRule (List (Maybe Name, PTerm))
constraints fname indents
    = do tm <- appExpr pdef fname indents
         decoratedSymbol fname "=>"
         more <- constraints fname indents
         pure ((Nothing, tm) :: more)
  <|> do decoratedSymbol fname "("
         n <- decorate fname Bound name
         decoratedSymbol fname ":"
         tm <- typeExpr pdef fname indents
         decoratedSymbol fname ")"
         decoratedSymbol fname "=>"
         more <- constraints fname indents
         pure ((Just n, tm) :: more)
  <|> pure []

implBinds : OriginDesc -> IndentInfo -> (namedImpl : Bool) -> EmptyRule (List (FC, RigCount, Name, PiInfo PTerm, PTerm))
implBinds fname indents namedImpl = concatMap (map adjust) <$> go where

  adjust : (RigCount, WithBounds Name, a) -> (FC, RigCount, Name, a)
  adjust (r, wn, ty) = (virtualiseFC (boundToFC fname wn), r, wn.val, ty)

  isDefaultImplicit : PiInfo a -> Bool
  isDefaultImplicit (DefImplicit _) = True
  isDefaultImplicit _               = False

  go : EmptyRule (List (List (RigCount, WithBounds Name, PiInfo PTerm, PTerm)))
  go = do decoratedSymbol fname "{"
          piInfo <- bounds $ option Implicit $ defImplicitField fname indents
          when (not namedImpl && isDefaultImplicit piInfo.val) $
            fatalLoc piInfo.bounds "Default implicits are allowed only for named implementations"
          ns <- map @{Compose} (\(rc, wb, n) => (rc, wb, piInfo.val, n)) $ pibindListName fname indents
          commitSymbol fname "}"
          commitSymbol fname "->"
          more <- go
          pure (ns :: more)
    <|> pure []

ifaceParam : OriginDesc -> IndentInfo -> Rule (List Name, (RigCount, PTerm))
ifaceParam fname indents
    = do decoratedSymbol fname "("
         rig <- multiplicity fname
         ns <- sepBy1 (decoratedSymbol fname ",") (decorate fname Bound name)
         decoratedSymbol fname ":"
         tm <- typeExpr pdef fname indents
         decoratedSymbol fname ")"
         pure (forget ns, (rig, tm))
  <|> do n <- bounds (decorate fname Bound name)
         pure ([n.val], (erased, PInfer (boundToFC fname n)))

ifaceDecl : OriginDesc -> IndentInfo -> Rule PDecl
ifaceDecl fname indents
    = do b <- bounds (do doc   <- optDocumentation fname
                         vis   <- visibility fname
                         col   <- column
                         decoratedKeyword fname "interface"
                         commit
                         cons   <- constraints fname indents
                         n      <- decorate fname Typ name
                         paramss <- many (ifaceParam fname indents)
                         let params = concatMap (\ (ns, rt) => map (\ n => (n, rt)) ns) paramss
                         det    <- option [] $ decoratedSymbol fname "|" *> sepBy (decoratedSymbol fname ",") (decorate fname Bound name)
                         decoratedKeyword fname "where"
                         dc <- optional (recordConstructor fname)
                         body <- blockAfter col (topDecl fname)
                         pure (\fc : FC => PInterface fc
                                      vis cons n doc params det dc (collectDefs (concat body))))
         pure (b.val (boundToFC fname b))

implDecl : OriginDesc -> IndentInfo -> Rule PDecl
implDecl fname indents
    = do b <- bounds (do doc     <- optDocumentation fname
                         visOpts <- many (visOpt fname)
                         vis     <- getVisibility Nothing visOpts
                         let opts = mapMaybe getRight visOpts
                         col <- column
                         option () (decoratedKeyword fname "implementation")
                         iname  <- optional $ decoratedSymbol fname "["
                                           *> decorate fname Function name
                                           <* decoratedSymbol fname "]"
                         impls  <- implBinds fname indents (isJust iname)
                         cons   <- constraints fname indents
                         n      <- decorate fname Typ name
                         params <- many (continue indents *> simpleExpr fname indents)
                         nusing <- option [] $ decoratedKeyword fname "using"
                                            *> forget <$> some (decorate fname Function name)
                         body <- optional $ decoratedKeyword fname "where" *> blockAfter col (topDecl fname)
                         pure $ \fc : FC =>
                            (PImplementation fc vis opts Single impls cons n params iname nusing
                                             (map (collectDefs . concat) body)))
         atEnd indents
         pure (b.val (boundToFC fname b))

fieldDecl : OriginDesc -> IndentInfo -> Rule (List PField)
fieldDecl fname indents
      = do doc <- optDocumentation fname
           decoratedSymbol fname "{"
           commit
           impl <- option Implicit (autoImplicitField fname indents <|> defImplicitField fname indents)
           fs <- fieldBody doc impl
           decoratedSymbol fname "}"
           atEnd indents
           pure fs
    <|> do doc <- optDocumentation fname
           fs <- fieldBody doc Explicit
           atEnd indents
           pure fs
  where
    fieldBody : String -> PiInfo PTerm -> Rule (List PField)
    fieldBody doc p = do
      b <- bounds (do
             rig <- multiplicity fname
             ns <- sepBy1 (decoratedSymbol fname ",")
                     (decorate fname Function name
                        <|> (do b <- bounds (symbol "_")
                                fatalLoc {c = True} b.bounds "Fields have to be named"))
             decoratedSymbol fname ":"
             ty <- typeExpr pdef fname indents
             pure (\fc : FC => map (\n => MkField fc doc rig p n ty) (forget ns)))
      pure (b.val (boundToFC fname b))

typedArg : OriginDesc -> IndentInfo -> Rule (List (Name, RigCount, PiInfo PTerm, PTerm))
typedArg fname indents
    = do params <- parens fname $ pibindListName fname indents
         pure $ map (\(c, n, tm) => (n.val, c, Explicit, tm)) params
  <|> do decoratedSymbol fname "{"
         commit
         info <-
                 (pure  AutoImplicit <* decoratedKeyword fname "auto"
              <|> (decoratedKeyword fname "default" *> DefImplicit <$> simpleExpr fname indents)
              <|> pure      Implicit)
         params <- pibindListName fname indents
         decoratedSymbol fname "}"
         pure $ map (\(c, n, tm) => (n.val, c, info, tm)) params

recordParam : OriginDesc -> IndentInfo -> Rule (List (Name, RigCount, PiInfo PTerm,  PTerm))
recordParam fname indents
    = typedArg fname indents
  <|> do n <- bounds (UN . Basic <$> decoratedSimpleBinderName fname)
         pure [(n.val, top, Explicit, PInfer (boundToFC fname n))]

-- A record without a where is a forward declaration
recordBody : OriginDesc -> IndentInfo ->
             String -> WithDefault Visibility Private ->
             Maybe TotalReq ->
             Int ->
             Name ->
             List (Name, RigCount, PiInfo PTerm, PTerm) ->
             EmptyRule (FC -> PDecl)
recordBody fname indents doc vis mbtot col n params
    = do atEndIndent indents
         pure (\fc : FC => PRecord fc doc vis mbtot (MkPRecordLater n params))
  <|> do mustWork $ decoratedKeyword fname "where"
         opts <- dataOpts fname
         dcflds <- blockWithOptHeaderAfter col
                     (\ idt => recordConstructor fname <* atEnd idt)
                     (fieldDecl fname)
         pure (\fc : FC => PRecord fc doc vis mbtot (MkPRecord n params opts (fst dcflds) (concat (snd dcflds))))

recordDecl : OriginDesc -> IndentInfo -> Rule PDecl
recordDecl fname indents
    = do b <- bounds (do doc         <- optDocumentation fname
                         (vis,mbtot) <- dataVisOpt fname
                         col         <- column
                         decoratedKeyword fname "record"
                         n       <- mustWork (decoratedDataTypeName fname)
                         paramss <- many (continue indents >> recordParam fname indents)
                         let params = concat paramss
                         recordBody fname indents doc vis mbtot col n params)
         pure (b.val (boundToFC fname b))

paramDecls : OriginDesc -> IndentInfo -> Rule PDecl
paramDecls fname indents = do
         startCol <- column
         b1 <- bounds (decoratedKeyword fname "parameters")
         commit
         args <- bounds (newParamDecls fname indents <|> oldParamDecls fname indents)
         commit
         declarations <- bounds $ nonEmptyBlockAfter startCol (topDecl fname)
         mergedBounds <- pure $ b1 `mergeBounds` (args `mergeBounds` declarations)
         pure (PParameters (boundToFC fname mergedBounds) args.val (collectDefs (concat declarations.val)))

  where
    oldParamDecls : OriginDesc -> IndentInfo -> Rule (List (Name, RigCount, PiInfo PTerm, PTerm))
    oldParamDecls fname indents
        = do decoratedSymbol fname "("
             ps <- sepBy (decoratedSymbol fname ",")
                         (do x <- UN . Basic <$> decoratedSimpleBinderName fname
                             decoratedSymbol fname ":"
                             ty <- typeExpr pdef fname indents
                             pure (x, top, Explicit, ty))
             decoratedSymbol fname ")"
             pure ps

    newParamDecls : OriginDesc -> IndentInfo -> Rule (List (Name, RigCount, PiInfo PTerm, PTerm))
    newParamDecls fname indents
        = map concat (some $ typedArg fname indents)


claims : OriginDesc -> IndentInfo -> Rule (List1 PDecl)
claims fname indents
    = do bs <- bounds (do
                  doc     <- optDocumentation fname
                  visOpts <- many (visOpt fname)
                  vis     <- getVisibility Nothing visOpts
                  let opts = mapMaybe getRight visOpts
                  rig  <- multiplicity fname
                  cls  <- tyDecls (decorate fname Function name)
                                  doc fname indents
                  pure $ map (\cl => the (Pair _ _) (doc, vis, opts, rig, cl)) cls)
         pure $ map (\(doc, vis, opts, rig, cl) : Pair _ _ =>
                           PClaim (boundToFC fname bs) rig vis opts cl)
                    bs.val

definition : OriginDesc -> IndentInfo -> Rule PDecl
definition fname indents
    = do nd <- bounds (clause 0 Nothing fname indents)
         pure (PDef (boundToFC fname nd) [nd.val])

operatorBindingKeyword : OriginDesc -> EmptyRule BindingModifier
operatorBindingKeyword fname
  =   (decoratedKeyword fname "autobind" >> pure Autobind)
  <|> (decoratedKeyword fname "typebind" >> pure Typebind)
  <|> pure NotBinding

fixDecl : OriginDesc -> IndentInfo -> Rule (List PDecl)
fixDecl fname indents
    = do vis <- exportVisibility fname
         binding <- operatorBindingKeyword fname
         b <- bounds (do fixity <- decorate fname Keyword $ fix
                         commit
                         prec <- decorate fname Keyword $ intLit
                         ops <- sepBy1 (decoratedSymbol fname ",") iOperator
                         pure (fixity, prec, ops))
         (fixity, prec, ops) <- pure b.val
         pure (map (PFixity (boundToFC fname b) vis binding fixity (fromInteger prec)) (forget ops))

directiveDecl : OriginDesc -> IndentInfo -> Rule PDecl
directiveDecl fname indents
    = do b <- bounds (directive fname indents)
         pure (PDirective (boundToFC fname b) b.val)

-- Declared at the top
-- topDecl : OriginDesc -> IndentInfo -> Rule (List PDecl)
topDecl fname indents
      -- Specifically check if the user has attempted to use a reserved identifier to begin their declaration to give improved error messages.
      -- i.e. the claim "String : Type" is a parse error, but the underlying reason may not be clear to new users.
    = do id <- anyReservedIdent
         the (Rule (List PDecl)) $ fatalLoc id.bounds "Cannot begin a declaration with a reserved identifier"
  <|> do d <- dataDecl fname indents
         pure [d]
  <|> do ds <- claims fname indents
         pure (forget ds)
  <|> do d <- directiveDecl fname indents
         pure [d]
  <|> do d <- implDecl fname indents
         pure [d]
  <|> do d <- definition fname indents
         pure [d]
  <|> fixDecl fname indents
  <|> do d <- ifaceDecl fname indents
         pure [d]
  <|> do d <- recordDecl fname indents
         pure [d]
  <|> do d <- namespaceDecl fname indents
         pure [d]
  <|> do d <- failDecls fname indents
         pure [d]
  <|> do d <- mutualDecls fname indents
         pure [d]
  <|> do d <- paramDecls fname indents
         pure [d]
  <|> do d <- usingDecls fname indents
         pure [d]
  <|> do d <- builtinDecl fname indents
         pure [d]
  <|> do d <- runElabDecl fname indents
         pure [d]
  <|> do d <- transformDecl fname indents
         pure [d]
  <|> do dstr <- bounds (terminal "Expected CG directive"
                          (\case
                             CGDirective d => Just d
                             _ => Nothing))
         pure [let cgrest = span isAlphaNum dstr.val in
                   PDirective (boundToFC fname dstr)
                        (CGAction (fst cgrest) (stripBraces (trim (snd cgrest))))]
      -- If the user tried to begin a declaration with any other keyword, then show a more informative error.
  <|> do kw <- bounds anyKeyword
         the (Rule (List PDecl)) $ fatalLoc kw.bounds "Keyword '\{kw.val}' is not a valid start to a declaration"
  <|> fatalError "Couldn't parse declaration"

-- All the clauses get parsed as one-clause definitions. Collect any
-- neighbouring clauses into one definition. This might mean merging two
-- functions which are different, if there are forward declarations,
-- but we'll split them in Desugar.idr. We can't do this now, because we
-- haven't resolved operator precedences yet.
-- Declared at the top.
-- collectDefs : List PDecl -> List PDecl
collectDefs [] = []
collectDefs (PDef annot cs :: ds)
    = let (csWithFC, rest) = spanBy isPDef ds
          cs' = cs ++ concat (map snd csWithFC)
          annot' = foldr
                   (\fc1, fc2 => fromMaybe EmptyFC (mergeFC fc1 fc2))
                   annot
                   (map fst csWithFC)
      in
          PDef annot' cs' :: assert_total (collectDefs rest)
collectDefs (PNamespace annot ns nds :: ds)
    = PNamespace annot ns (collectDefs nds) :: collectDefs ds
collectDefs (PMutual annot nds :: ds)
    = PMutual annot (collectDefs nds) :: collectDefs ds
collectDefs (d :: ds)
    = d :: collectDefs ds

export
import_ : OriginDesc -> IndentInfo -> Rule Import
import_ fname indents
    = do b <- bounds (do decoratedKeyword fname "import"
                         reexp <- option False (decoratedKeyword fname "public" $> True)
                         ns <- decorate fname Module $ mustWork moduleIdent
                         nsAs <- option (miAsNamespace ns)
                                        (do decorate fname Keyword $ exactIdent "as"
                                            decorate fname Namespace $ mustWork namespaceId)
                         pure (reexp, ns, nsAs))
         atEnd indents
         (reexp, ns, nsAs) <- pure b.val
         pure (MkImport (boundToFC fname b) reexp ns nsAs)

export
progHdr : OriginDesc -> EmptyRule Module
progHdr fname
    = do b <- bounds (do doc    <- optDocumentation fname
                         nspace <- option (nsAsModuleIdent mainNS)
                                     (do decoratedKeyword fname "module"
                                         decorate fname Module $ mustWork moduleIdent)
                         imports <- block (import_ fname)
                         pure (doc, nspace, imports))
         (doc, nspace, imports) <- pure b.val
         pure (MkModule (boundToFC fname b)
                        nspace imports doc [])

export
prog : OriginDesc -> EmptyRule Module
prog fname
    = do mod <- progHdr fname
         ds <- block (topDecl fname)
         pure $ { decls := collectDefs (concat ds)} mod

parseMode : Rule REPLEval
parseMode
     = do exactIdent "typecheck"
          pure EvalTC
   <|> do exactIdent "tc"
          pure EvalTC
   <|> do exactIdent "normalise"
          pure NormaliseAll
   <|> do exactIdent "default"
          pure NormaliseAll
   <|> do exactIdent "normal"
          pure NormaliseAll
   <|> do exactIdent "normalize" -- oh alright then
          pure NormaliseAll
   <|> do exactIdent "execute"
          pure Execute
   <|> do exactIdent "exec"
          pure Execute
   <|> do exactIdent "scheme"
          pure Scheme

setVarOption : Rule REPLOpt
setVarOption
    = do exactIdent "eval"
         mode <- option NormaliseAll parseMode
         pure (EvalMode mode)
  <|> do exactIdent "editor"
         e <- unqualifiedName
         pure (Editor e)
  <|> do exactIdent "cg"
         c <- unqualifiedName
         pure (CG c)

setOption : Bool -> Rule REPLOpt
setOption set
    = do exactIdent "showimplicits"
         pure (ShowImplicits set)
  <|> do exactIdent "shownamespace"
         pure (ShowNamespace set)
  <|> do exactIdent "showmachinenames"
         pure (ShowMachineNames set)
  <|> do exactIdent "showtypes"
         pure (ShowTypes set)
  <|> do exactIdent "profile"
         pure (Profile set)
  <|> do exactIdent "evaltiming"
         pure (EvalTiming set)
  <|> if set then setVarOption else fatalError "Unrecognised option"

replCmd : List String -> Rule ()
replCmd [] = fail "Unrecognised command"
replCmd (c :: cs)
    = exactIdent c
  <|> symbol c
  <|> replCmd cs

cmdName : String -> Rule String
cmdName str = do
  _ <- optional (symbol ":")
  terminal ("Unrecognised REPL command '" ++ str ++ "'") $
           \case
              (Ident s)       => if s == str then Just s else Nothing
              (Keyword kw)    => if kw == str then Just kw else Nothing
              (Symbol "?")    => Just "?"
              (Symbol ":?")   => Just "?"   -- `:help :?` is a special case
              _ => Nothing

export
data CmdArg : Type where
     ||| The command takes no arguments.
     NoArg : CmdArg

     ||| The command takes a name.
     NameArg : CmdArg

     ||| The command takes an expression.
     ExprArg : CmdArg

     ||| The command takes a documentation directive.
     DocArg : CmdArg

     ||| The command takes a list of declarations
     DeclsArg : CmdArg

     ||| The command takes a number.
     NumberArg : CmdArg

     ||| The command takes a number or auto.
     AutoNumberArg : CmdArg

     ||| The command takes an option.
     OptionArg : CmdArg

     ||| The command takes a file.
     FileArg : CmdArg

     ||| The command takes a module.
     ModuleArg : CmdArg

     ||| The command takes a string
     StringArg : CmdArg

     ||| The command takes a on or off.
     OnOffArg : CmdArg

     ||| The command takes an argument documenting its name
     NamedCmdArg : String -> CmdArg -> CmdArg

     ||| The command takes an argument documenting its default value
     WithDefaultArg : String -> CmdArg -> CmdArg

     ||| The command takes arguments separated by commas
     CSVArg : CmdArg -> CmdArg

     ||| The command takes multiple arguments.
     Args : List CmdArg -> CmdArg

mutual
  covering
  showCmdArg : CmdArg -> String
  showCmdArg NoArg = ""
  showCmdArg NameArg = "name"
  showCmdArg ExprArg = "expr"
  showCmdArg DocArg = "keyword|expr"
  showCmdArg DeclsArg = "decls"
  showCmdArg NumberArg = "number"
  showCmdArg AutoNumberArg = "number|auto"
  showCmdArg OptionArg = "option"
  showCmdArg FileArg = "file"
  showCmdArg ModuleArg = "module"
  showCmdArg StringArg = "string"
  showCmdArg OnOffArg = "(on|off)"
  showCmdArg (CSVArg arg) = "[" ++ showCmdArg arg ++ "]"
  showCmdArg (WithDefaultArg value arg) = showCmdArg arg ++ "|" ++ value
  showCmdArg (NamedCmdArg name arg) = name ++ ":" ++ showCmdArg arg
  showCmdArg args@(Args _) = show args

  export
  covering
  Show CmdArg where
    show NoArg = ""
    show OnOffArg = "(on|off)"
    show (Args args) = showSep " " (map show args)
    show arg = "<" ++ showCmdArg arg ++ ">"

public export
knownCommands : List (String, String)
knownCommands =
  explain ["t", "type"] "Check the type of an expression" ++
  [ ("ti", "Check the type of an expression, showing implicit arguments")
  , ("printdef", "Show the definition of a pattern-matching function")
  ] ++
  explain ["s", "search"] "Search for values by type" ++
  [ ("di", "Show debugging information for a name")
  ] ++
  explain ["module", "import"] "Import an extra module" ++
  [ ("package", "Import every module of the package")
  ] ++
  explain ["q", "quit", "exit"] "Exit the Idris system" ++
  [ ("cwd", "Displays the current working directory")
  , ("cd", "Change the current working directory")
  , ("sh", "Run a shell command")
  , ("set"
    , unlines   -- FIXME: this should be a multiline string (see #2087)
      [ "Set an option"
      , "  eval                specify what evaluation mode to use:"
      , "                        typecheck|tc"
      , "                        normalise|normalize|normal"
      , "                        execute|exec"
      , "                        scheme"
      , ""
      , "  editor              specify the name of the editor command"
      , ""
      , "  cg                  specify the codegen/backend to use"
      , "                      builtin codegens are:"
      , "                        chez"
      , "                        racket"
      , "                        refc"
      , "                        node"
      , ""
      , "  showimplicits       enable displaying implicit arguments as part of the"
      , "                      output"
      , ""
      , "  shownamespace       enable displaying namespaces as part of the output"
      , ""
      , "  showmachinenames    enable displaying machine names as part of the"
      , "                      output"
      , ""
      , "  showtypes           enable displaying the type of the term as part of"
      , "                      the output"
      , ""
      , "  profile"
      , ""
      , "  evaltiming          enable timing how long evaluation takes and"
      , "                      displaying this before the printing of the output"
      ]
    )
  , ("unset", "Unset an option")
  , ("opts", "Show current options settings")
  ] ++
  explain ["c", "compile"] "Compile to an executable" ++
  [ ("exec", "Compile to an executable and run")
  , ("directive", "Set a codegen-specific directive")
  ] ++
  explain ["l", "load"] "Load a file" ++
  explain ["r", "reload"] "Reload current file" ++
  explain ["e", "edit"] "Edit current file using $EDITOR or $VISUAL" ++
  explain ["miss", "missing"] "Show missing clauses" ++
  [ ("total", "Check the totality of a name")
  , ("doc", "Show documentation for a keyword, a name, or a primitive")
  , ("browse", "Browse contents of a namespace")
  ] ++
  explain ["log", "logging"] "Set logging level" ++
  [ ("consolewidth", "Set the width of the console output (0 for unbounded) (auto by default)")
  ] ++
  explain ["colour", "color"] "Whether to use colour for the console output (enabled by default)" ++
  explain ["m", "metavars"] "Show remaining proof obligations (metavariables or holes)" ++
  [ ("typeat", "Show type of term <n> defined on line <l> and column <c>")
  ] ++
  explain ["cs", "casesplit"] "Case split term <n> defined on line <l> and column <c>" ++
  explain ["ac", "addclause"] "Add clause to term <n> defined on line <l>" ++
  explain ["ml", "makelemma"] "Make lemma for term <n> defined on line <l>" ++
  explain ["mc", "makecase"] "Make case on term <n> defined on line <l>" ++
  explain ["mw", "makewith"] "Add with expression on term <n> defined on line <l>" ++
  [ ("intro", "Introduce unambiguous constructor in hole <n> defined on line <l>")
  , ("refine", "Refine hole <h> with identifier <n> on line <l> and column <c>")
  ] ++
  explain ["ps", "proofsearch"] "Search for a proof" ++
  [ ("psnext", "Show next proof")
  , ("gd", "Try to generate a definition using proof-search")
  , ("gdnext", "Show next definition")
  , ("version", "Display the Idris version")
  ] ++
  explain ["?", "h", "help"] (unlines     -- FIXME: this should be a multiline string (see #2087)
        [ "Display help text, optionally of a specific command.\n"
        , "If run without arguments, lists all the REPL commands along with their"
        , "initial line of help text.\n"
        , "More detailed help can then be obtained by running the :help command"
        , "with another command as an argument, e.g."
        , "  > :help :help"
        , "  > :help :set"
        , "(the leading ':' in the command argument is optional)"
        ] ) ++
  [ ( "let"
    , """
      Define a new value.

      First, declare the type of your new value, e.g.
        :let myValue : List Nat

      Then, define the value:
        :let myValue = [1, 2, 3]

      Now the value is in scope at the REPL:
        > map (+ 2) myValue
        [3, 4, 5]
      """
    )
  ] ++
  explain ["fs", "fsearch"] "Search for global definitions by sketching the names distribution of the wanted type(s)."
  where
    explain : List String -> String -> List (String, String)
    explain cmds expl = map (\s => (s, expl)) cmds

public export
KnownCommand : String -> Type
KnownCommand cmd = IsJust (lookup cmd knownCommands)

export
data ParseCmd : Type where
     ParseREPLCmd :  (cmds : List String)
                  -> {auto 0 _ : All KnownCommand cmds}
                  -> ParseCmd

     ParseKeywordCmd :  (cmds : List String)
                     -> {auto 0 _ : All KnownCommand cmds}
                     -> ParseCmd

     ParseIdentCmd :  (cmd : String)
                   -> {auto 0 _ : KnownCommand cmd}
                   -> ParseCmd

public export
CommandDefinition : Type
CommandDefinition = (List String, CmdArg, String, Rule REPLCmd)

public export
CommandTable : Type
CommandTable = List CommandDefinition

extractNames : ParseCmd -> List String
extractNames (ParseREPLCmd names) = names
extractNames (ParseKeywordCmd keywords) = keywords
extractNames (ParseIdentCmd ident) = [ident]

runParseCmd : ParseCmd -> Rule ()
runParseCmd (ParseREPLCmd names) = replCmd names
runParseCmd (ParseKeywordCmd keywords) = choice $ map keyword keywords
runParseCmd (ParseIdentCmd ident) = exactIdent ident


noArgCmd : ParseCmd -> REPLCmd -> String -> CommandDefinition
noArgCmd parseCmd command doc = (names, NoArg, doc, parse)
  where
    names : List String
    names = extractNames parseCmd

    parse : Rule REPLCmd
    parse = do
      symbol ":"
      runParseCmd parseCmd
      pure command

nameArgCmd : ParseCmd -> (Name -> REPLCmd) -> String -> CommandDefinition
nameArgCmd parseCmd command doc = (names, NameArg, doc, parse)
  where
    names : List String
    names = extractNames parseCmd

    parse : Rule REPLCmd
    parse = do
      symbol ":"
      runParseCmd parseCmd
      n <- mustWork name
      pure (command n)

stringArgCmd : ParseCmd -> (String -> REPLCmd) -> String -> CommandDefinition
stringArgCmd parseCmd command doc = (names, StringArg, doc, parse)
  where
    names : List String
    names = extractNames parseCmd

    parse : Rule REPLCmd
    parse = do
      symbol ":"
      runParseCmd parseCmd
      s <- mustWork simpleStr
      pure (command s)

getHelpType : EmptyRule HelpType
getHelpType = do
  optCmd <- optional $ choice $ (cmdName . fst) <$> knownCommands
  pure $
    case optCmd of
         Nothing => GenericHelp
         Just cmd => DetailedHelp $ fromMaybe "Unrecognised command '\{cmd}'"
                                  $ lookup cmd knownCommands

helpCmd :  ParseCmd
        -> (HelpType -> REPLCmd)
        -> String
        -> CommandDefinition
helpCmd parseCmd command doc = (names, StringArg, doc, parse)
  where
    names : List String
    names = extractNames parseCmd

    parse : Rule REPLCmd
    parse = do
      symbol ":"
      runParseCmd parseCmd
      helpType <- getHelpType
      pure (command helpType)

moduleArgCmd : ParseCmd -> (ModuleIdent -> REPLCmd) -> String -> CommandDefinition
moduleArgCmd parseCmd command doc = (names, ModuleArg, doc, parse)
  where
    names : List String
    names = extractNames parseCmd

    parse : Rule REPLCmd
    parse = do
      symbol ":"
      runParseCmd parseCmd
      n <- mustWork moduleIdent
      pure (command n)

exprArgCmd : ParseCmd -> (PTerm -> REPLCmd) -> String -> CommandDefinition
exprArgCmd parseCmd command doc = (names, ExprArg, doc, parse)
  where
    names : List String
    names = extractNames parseCmd

    parse : Rule REPLCmd
    parse = do
      symbol ":"
      runParseCmd parseCmd
      tm <- mustWork $ typeExpr pdef (Virtual Interactive) init
      pure (command tm)

docArgCmd : ParseCmd -> (DocDirective -> REPLCmd) -> String -> CommandDefinition
docArgCmd parseCmd command doc = (names, DocArg, doc, parse)
  where
    names : List String
    names = extractNames parseCmd

    -- by default, lazy primitives must be followed by a simpleExpr, so we have
    -- this custom parser for the doc case
    docLazyPrim : Rule PTerm
    docLazyPrim =
      let placeholeder : PTerm' Name
          placeholeder = PHole EmptyFC False "lazyDocPlaceholeder"
      in  do exactIdent "Lazy"    -- v
             pure (PDelayed EmptyFC LLazy placeholeder)
      <|> do exactIdent "Inf"     -- v
             pure (PDelayed EmptyFC LInf placeholeder)
      <|> do exactIdent "Delay"
             pure (PDelay EmptyFC placeholeder)
      <|> do exactIdent "Force"
             pure (PForce EmptyFC placeholeder)

    parse : Rule REPLCmd
    parse = do
      symbol ":"
      runParseCmd parseCmd
      dir <- mustWork $
        AModule <$ keyword "module" <*> moduleIdent -- must be before Keyword to not be captured
        <|> Keyword <$> anyKeyword
        <|> Symbol <$> (anyReservedSymbol <* eoi
                       <|> parens (Virtual Interactive) anyReservedSymbol <* eoi)
        <|> Bracket <$> (
              IdiomBrackets <$ symbol "[|" <* symbol "|]"
              <|> NameQuote <$ symbol "`{" <* symbol "}"
              <|> TermQuote <$ symbol "`(" <* symbol ")"
              <|> DeclQuote <$ symbol "`[" <* symbol "]"
              )
        <|> APTerm <$> (
              docLazyPrim
              <|> typeExpr pdef (Virtual Interactive) init
              )
      pure (command dir)

declsArgCmd : ParseCmd -> (List PDecl -> REPLCmd) -> String -> CommandDefinition
declsArgCmd parseCmd command doc = (names, DeclsArg, doc, parse)
  where
    names : List String
    names = extractNames parseCmd
    parse : Rule REPLCmd
    parse = do
      symbol ":"
      runParseCmd parseCmd
      tm <- mustWork $ topDecl (Virtual Interactive) init
      pure (command tm)

optArgCmd : ParseCmd -> (REPLOpt -> REPLCmd) -> Bool -> String -> CommandDefinition
optArgCmd parseCmd command set doc = (names, OptionArg, doc, parse)
  where
    names : List String
    names = extractNames parseCmd

    parse : Rule REPLCmd
    parse = do
      symbol ":"
      runParseCmd parseCmd
      opt <- mustWork $ setOption set
      pure (command opt)

numberArgCmd : ParseCmd -> (Nat -> REPLCmd) -> String -> CommandDefinition
numberArgCmd parseCmd command doc = (names, NumberArg, doc, parse)
  where
    names : List String
    names = extractNames parseCmd

    parse : Rule REPLCmd
    parse = do
      symbol ":"
      runParseCmd parseCmd
      i <- mustWork intLit
      pure (command (fromInteger i))

autoNumberArgCmd : ParseCmd -> (Maybe Nat -> REPLCmd) -> String -> CommandDefinition
autoNumberArgCmd parseCmd command doc = (names, AutoNumberArg, doc, parse)
  where
    names : List String
    names = extractNames parseCmd

    autoNumber : Rule (Maybe Nat)
    autoNumber = Nothing <$ keyword "auto"
             <|> Just . fromInteger <$> intLit

    parse : Rule REPLCmd
    parse = do
      symbol ":"
      runParseCmd parseCmd
      mi <- mustWork autoNumber
      pure (command mi)

onOffArgCmd : ParseCmd -> (Bool -> REPLCmd) -> String -> CommandDefinition
onOffArgCmd parseCmd command doc = (names, OnOffArg, doc, parse)
  where
    names : List String
    names = extractNames parseCmd

    parse : Rule REPLCmd
    parse = do
      symbol ":"
      runParseCmd parseCmd
      i <- mustWork onOffLit
      pure (command i)

compileArgsCmd : ParseCmd -> (PTerm -> String -> REPLCmd) -> String -> CommandDefinition
compileArgsCmd parseCmd command doc
    = (names, Args [FileArg, ExprArg], doc, parse)
  where
    names : List String
    names = extractNames parseCmd

    parse : Rule REPLCmd
    parse = do
      symbol ":"
      runParseCmd parseCmd
      n <- mustWork unqualifiedName
      tm <- mustWork $ expr pdef (Virtual Interactive) init
      pure (command tm n)

loggingArgCmd : ParseCmd -> (Maybe LogLevel -> REPLCmd) -> String -> CommandDefinition
loggingArgCmd parseCmd command doc = (names, Args [StringArg, NumberArg], doc, parse) where

  names : List String
  names = extractNames parseCmd

  parse : Rule REPLCmd
  parse = do
    symbol ":"
    runParseCmd parseCmd
    lvl <- mustWork $ logLevel (Virtual Interactive)
    pure (command lvl)

editLineNameArgCmd : ParseCmd -> (Bool -> Int -> Name -> EditCmd) -> String -> CommandDefinition
editLineNameArgCmd parseCmd command doc = (names, Args [NamedCmdArg "l" NumberArg, NamedCmdArg "n" StringArg], doc, parse) where

  names : List String
  names = extractNames parseCmd

  parse : Rule REPLCmd
  parse = do
    symbol ":"
    runParseCmd parseCmd
    upd <- option False (symbol "!" $> True)
    line <- fromInteger <$> mustWork intLit
    n <- mustWork name
    pure (Editing $ command upd line n)

editLineColNameArgCmd : ParseCmd -> (Bool -> Int -> Int -> Name -> EditCmd) -> String -> CommandDefinition
editLineColNameArgCmd parseCmd command doc =
  ( names
  , Args [ NamedCmdArg "l" NumberArg
         , NamedCmdArg "c" NumberArg
         , NamedCmdArg "n" StringArg
         ]
  , doc
  , parse
  ) where

  names : List String
  names = extractNames parseCmd

  parse : Rule REPLCmd
  parse = do
    symbol ":"
    runParseCmd parseCmd
    upd <- option False (symbol "!" $> True)
    line <- fromInteger <$> mustWork intLit
    col <- fromInteger <$> mustWork intLit
    n <- mustWork name
    pure (Editing $ command upd line col n)

editLineNamePTermArgCmd : ParseCmd -> (Bool -> Int -> Name -> PTerm -> EditCmd) -> String -> CommandDefinition
editLineNamePTermArgCmd parseCmd command doc =
  ( names
  , Args [ NamedCmdArg "l" NumberArg
         , NamedCmdArg "c" NumberArg
         , NamedCmdArg "h" StringArg
         , NamedCmdArg "e" ExprArg
         ]
  , doc
  , parse
  ) where

  names : List String
  names = extractNames parseCmd

  parse : Rule REPLCmd
  parse = do
    symbol ":"
    runParseCmd parseCmd
    upd <- option False (symbol "!" $> True)
    line <- fromInteger <$> mustWork intLit
    h <- mustWork name
    n <- mustWork $ typeExpr pdef (Virtual Interactive) init
    pure (Editing $ command upd line h n)

editLineNameCSVArgCmd : ParseCmd
                       -> (Bool -> Int -> Name -> List Name -> EditCmd)
                       -> String
                       -> CommandDefinition
editLineNameCSVArgCmd parseCmd command doc =
  ( names
  , Args [ NamedCmdArg "l" NumberArg
         , NamedCmdArg "n" StringArg
         , NamedCmdArg "h" (CSVArg NameArg)
         ]
  , doc
  , parse
  ) where

  names : List String
  names = extractNames parseCmd

  parse : Rule REPLCmd
  parse = do
    symbol ":"
    runParseCmd parseCmd
    upd <- option False (symbol "!" $> True)
    line <- fromInteger <$> mustWork intLit
    n <- mustWork name
    hints <- mustWork $ sepBy (symbol ",") name
    pure (Editing $ command upd line n hints)

editLineNameOptionArgCmd : ParseCmd
                        -> (Bool -> Int -> Name -> Nat -> EditCmd)
                        -> String
                        -> CommandDefinition
editLineNameOptionArgCmd parseCmd command doc =
  ( names
  , Args [ NamedCmdArg "l" NumberArg
         , NamedCmdArg "n" StringArg
         , NamedCmdArg "r" (WithDefaultArg "0" NumberArg)
         ]
  , doc
  , parse
  ) where

  names : List String
  names = extractNames parseCmd

  parse : Rule REPLCmd
  parse = do
    symbol ":"
    runParseCmd parseCmd
    upd <- option False (symbol "!" $> True)
    line <- fromInteger <$> mustWork intLit
    n <- mustWork name
    nreject <- fromInteger <$> option 0 intLit
    pure (Editing $ command upd line n nreject)

firstHelpLine : (cmd : String) -> {auto 0 _ : KnownCommand cmd} -> String
firstHelpLine cmd =
  head . (split ((==) '\n')) $
  fromMaybe "Failed to look up '\{cmd}' (SHOULDN'T HAPPEN!)" $
  lookup cmd knownCommands

export
parserCommandsForHelp : CommandTable
parserCommandsForHelp =
  [ exprArgCmd (ParseREPLCmd ["t", "type"]) Check (firstHelpLine "t")
  , exprArgCmd (ParseREPLCmd ["ti"]) CheckWithImplicits (firstHelpLine "ti")
  , exprArgCmd (ParseREPLCmd ["printdef"]) PrintDef (firstHelpLine "printdef")
  , exprArgCmd (ParseREPLCmd ["s", "search"]) TypeSearch (firstHelpLine "s")
  , nameArgCmd (ParseIdentCmd "di") DebugInfo (firstHelpLine "di")
  , moduleArgCmd (ParseKeywordCmd ["module", "import"]) ImportMod (firstHelpLine "module")
  , stringArgCmd (ParseREPLCmd ["package"]) ImportPackage (firstHelpLine "package")
  , noArgCmd (ParseREPLCmd ["q", "quit", "exit"]) Quit (firstHelpLine "q")
  , noArgCmd (ParseREPLCmd ["cwd"]) CWD (firstHelpLine "cwd")
  , stringArgCmd (ParseREPLCmd ["cd"]) CD (firstHelpLine "cd")
  , stringArgCmd (ParseREPLCmd ["sh"]) RunShellCommand (firstHelpLine "sh")
  , optArgCmd (ParseIdentCmd "set") SetOpt True (firstHelpLine "set")
  , optArgCmd (ParseIdentCmd "unset") SetOpt False (firstHelpLine "unset")
  , noArgCmd (ParseREPLCmd ["opts"]) GetOpts (firstHelpLine "opts")
  , compileArgsCmd (ParseREPLCmd ["c", "compile"]) Compile (firstHelpLine "c")
  , exprArgCmd (ParseIdentCmd "exec") Exec (firstHelpLine "exec")
  , stringArgCmd (ParseIdentCmd "directive") CGDirective (firstHelpLine "directive")
  , stringArgCmd (ParseREPLCmd ["l", "load"]) Load (firstHelpLine "l")
  , noArgCmd (ParseREPLCmd ["r", "reload"]) Reload (firstHelpLine "r")
  , noArgCmd (ParseREPLCmd ["e", "edit"]) Edit (firstHelpLine "e")
  , nameArgCmd (ParseREPLCmd ["miss", "missing"]) Missing (firstHelpLine "miss")
  , nameArgCmd (ParseKeywordCmd ["total"]) Total (firstHelpLine "total")
  , docArgCmd (ParseIdentCmd "doc") Doc (firstHelpLine "doc")
  , moduleArgCmd (ParseIdentCmd "browse") (Browse . miAsNamespace) (firstHelpLine "browse")
  , loggingArgCmd (ParseREPLCmd ["log", "logging"]) SetLog (firstHelpLine "log")
  , autoNumberArgCmd (ParseREPLCmd ["consolewidth"]) SetConsoleWidth (firstHelpLine "consolewidth")
  , onOffArgCmd (ParseREPLCmd ["colour", "color"]) SetColor (firstHelpLine "colour")
  , noArgCmd (ParseREPLCmd ["m", "metavars"]) Metavars (firstHelpLine "m")
  , editLineColNameArgCmd (ParseREPLCmd ["typeat"]) (const TypeAt) (firstHelpLine "typeat")
  , editLineColNameArgCmd (ParseREPLCmd ["cs", "casesplit"]) CaseSplit (firstHelpLine "cs")
  , editLineNameArgCmd (ParseREPLCmd ["ac", "addclause"]) AddClause (firstHelpLine "ac")
  , editLineNameArgCmd (ParseREPLCmd ["ml", "makelemma"]) MakeLemma (firstHelpLine "ml")
  , editLineNameArgCmd (ParseREPLCmd ["mc", "makecase"]) MakeCase (firstHelpLine "mc")
  , editLineNameArgCmd (ParseREPLCmd ["mw", "makewith"]) MakeWith (firstHelpLine "mw")
  , editLineNameArgCmd (ParseREPLCmd ["intro"]) Intro (firstHelpLine "intro")
  , editLineNamePTermArgCmd (ParseREPLCmd ["refine"]) Refine (firstHelpLine "refine")
  , editLineNameCSVArgCmd (ParseREPLCmd ["ps", "proofsearch"]) ExprSearch (firstHelpLine "ps")
  , noArgCmd (ParseREPLCmd ["psnext"]) (Editing ExprSearchNext) (firstHelpLine "psnext")
  , editLineNameOptionArgCmd (ParseREPLCmd ["gd"]) GenerateDef (firstHelpLine "gd")
  , noArgCmd (ParseREPLCmd ["gdnext"]) (Editing GenerateDefNext) (firstHelpLine "gdnext")
  , noArgCmd (ParseREPLCmd ["version"]) ShowVersion (firstHelpLine "version")
  , helpCmd (ParseREPLCmd ["?", "h", "help"]) Help (firstHelpLine "?")
  , declsArgCmd (ParseKeywordCmd ["let"]) NewDefn (firstHelpLine "let")
  , exprArgCmd (ParseREPLCmd ["fs", "fsearch"]) FuzzyTypeSearch (firstHelpLine "fs")
  ]

export
help : List (List String, CmdArg, String)
help = (["<expr>"], NoArg, "Evaluate an expression") ::
         map (\ (names, args, text, _) =>
               (map (":" ++) names, args, text)) parserCommandsForHelp

nonEmptyCommand : Rule REPLCmd
nonEmptyCommand =
  choice (map (\ (_, _, _, parser) => parser) parserCommandsForHelp)

eval : Rule REPLCmd
eval = do
  tm <- typeExpr pdef (Virtual Interactive) init
  pure (Eval tm)

export
aPTerm : Rule PTerm
aPTerm = typeExpr pdef (Virtual Interactive) init

export
command : EmptyRule REPLCmd
command
    = eoi $> NOP
  <|> nonEmptyCommand
  <|> (do symbol ":?" -- special case, :? doesn't fit into above scheme
          helpType <- getHelpType
          pure $ Help helpType)
  <|> eval