Introduce a version of intercalate on Foldables instead of List. #71

src/Language/Common.hs

@@ -2,7 +2,8 @@
 ,LiberalTypeSynonyms, ImpredicativeTypes, UndecidableInstances, FunctionalDependencies #-}
 
 module Language.Common where
-import Data.Map.Strict as Map
+import Data.Map.Strict as Map hiding (foldl)
+import Data.Foldable (foldl)
 
 type a + b = Either a b
 
@@ -30,3 +31,11 @@ lookup2 :: Ord k => k -> Map k a -> a
 lookup2 m x = case Map.lookup m x of
   Just y -> y
   Nothing -> undefined
+
+-- | A version of intercalate that works on Foldables instead of just List,
+-- | adapted from PureScript.
+intercalate :: (Foldable f, Monoid m) => m -> f m -> m
+intercalate sep xs = snd (foldl go (True, mempty) xs)
+  where
+    go (True, _)   x = (False, x)
+    go (_   , acc) x = (False, acc <> sep <> x)

src/Language/Instance.hs

@@ -5,7 +5,7 @@ module Language.Instance where
 import Prelude hiding (EQ)
 import Data.Set as Set
 import Data.Map.Strict as Map
-import Data.List
+import Data.List hiding (intercalate)
 import Language.Common
 import Language.Term as Term
 import Language.Typeside as Typeside

src/Language/Mapping.hs

@@ -11,7 +11,6 @@ import Language.Common
 import Data.Typeable
 import Data.Set as Set
 import Data.Maybe
-import Data.List
 
 
 

src/Language/Program.hs

@@ -14,7 +14,6 @@ import Language.Mapping as M
 import Language.Typeside as T
 import Language.Transform as Tr
 import Language.Query as Q
-import Data.List (intercalate)
 
 
 data Exp =

src/Language/Schema.hs

@@ -12,7 +12,6 @@ import Language.Typeside
 import Language.Options
 import Language.Prover
 import Data.Typeable
-import Data.List (intercalate)
 import Data.Maybe
 
 

src/Language/Term.hs

@@ -7,7 +7,6 @@ import Prelude hiding (EQ)
 import Data.Set as Set hiding (size, foldr)
 import Data.Map.Strict as Map hiding (size, foldr)
 import Data.Void
-import Data.List (intercalate)
 import Language.Common
 import Data.Maybe
 

src/Language/Transform.hs

@@ -14,7 +14,6 @@ import Data.Void
 import Language.Schema as S
 import Data.Typeable
 import Data.Maybe
-import Data.List
 import Language.Options
 
 evalSigmaTrans

src/Language/Typeside.hs

@@ -11,7 +11,6 @@ import Data.Void
 import Language.Prover
 import Language.Options
 import Data.Typeable
-import Data.List (intercalate)
 
 fromList'' :: (Show k, Ord k) => [k] -> Err (Set k)
 fromList'' (k:l) = do l' <- fromList'' l