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Merge pull request #586 from lixitrixi/rule-groups
Implement rule priority groups to tree_morph
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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))); | ||
| } |