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tree_morph: implement rule priority groups
the main engine has been updated to make use of Uniplate's wonderful "contexts" method to abstract over and optimise the actual tree traversal. bump uniplate version update documentation
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,85 @@ | ||
| //! Here we test the `reduce_with_rule_groups` function. | ||
| //! Each rule group is applied to the whole tree as with `reduce_with_rules`, before the next group is tried. | ||
| //! Every time a change is made, the algorithm starts again with the first group. | ||
| //! | ||
| //! This lets us make powerful "evaluation" rules which greedily reduce the tree as much as possible, before other | ||
| //! "rewriting" rules are applied. | ||
| use tree_morph::{helpers::select_first, *}; | ||
| use uniplate::derive::Uniplate; | ||
|
|
||
| /// A simple language of two literals and a wrapper | ||
| #[derive(Debug, Clone, PartialEq, Eq, Uniplate)] | ||
| #[uniplate()] | ||
| enum Expr { | ||
| A, // a | ||
| B, // b | ||
| Wrap(Box<Expr>), // [E] | ||
| } | ||
|
|
||
| /// Rule container: holds a primitive function and implements the Rule trait | ||
| struct Rl(fn(&Expr) -> Option<Expr>); | ||
|
|
||
| impl Rule<Expr, ()> for Rl { | ||
| fn apply(&self, cmd: &mut Commands<Expr, ()>, expr: &Expr, _: &()) -> Option<Expr> { | ||
| self.0(expr) | ||
| } | ||
| } | ||
|
|
||
| mod rules { | ||
| use super::*; | ||
|
|
||
| /// [a] ~> a | ||
| pub fn unwrap_a(expr: &Expr) -> Option<Expr> { | ||
| if let Expr::Wrap(inner) = expr { | ||
| if let Expr::A = **inner { | ||
| return Some(Expr::A); | ||
| } | ||
| } | ||
| None | ||
| } | ||
|
|
||
| /// a ~> b | ||
| pub fn a_to_b(expr: &Expr) -> Option<Expr> { | ||
| if let Expr::A = expr { | ||
| return Some(Expr::B); | ||
| } | ||
| None | ||
| } | ||
| } | ||
|
|
||
| #[test] | ||
| fn test_same_group() { | ||
| // If the rules are in the same group, unwrap_a will apply higher in the tree | ||
|
|
||
| // [a] | ||
| let expr = Expr::Wrap(Box::new(Expr::A)); | ||
|
|
||
| let (expr, _) = reduce_with_rule_groups( | ||
| &[&[Rl(rules::unwrap_a), Rl(rules::a_to_b)]], | ||
| select_first, | ||
| expr, | ||
| (), | ||
| ); | ||
|
|
||
| // [a] ~> a ~> b | ||
| assert_eq!(expr, Expr::B); | ||
| } | ||
|
|
||
| #[test] | ||
| fn test_a_to_b_first() { | ||
| // a_to_b is in a higher group than unwrap_a, so it will be applied first to the lower expression | ||
|
|
||
| // [a] | ||
| let expr = Expr::Wrap(Box::new(Expr::A)); | ||
|
|
||
| let (expr, _) = reduce_with_rule_groups( | ||
| &[&[Rl(rules::a_to_b)], &[Rl(rules::unwrap_a)]], | ||
| select_first, | ||
| expr, | ||
| (), | ||
| ); | ||
|
|
||
| // [a] ~> [b] | ||
| assert_eq!(expr, Expr::Wrap(Box::new(Expr::B))); | ||
| } |