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use std::rc::Rc; use crate::{Analysis, EGraph, Id, Language, SearchMatches, Subst}; /// A rewrite that searches for the lefthand side and applies the righthand side. /// /// The [`rewrite!`] is the easiest way to create rewrites. /// /// A [`Rewrite`] consists principally of a [`Searcher`] (the lefthand /// side) and an [`Applier`] (the righthand side). /// It additionally stores a name used to refer to the rewrite and a /// long name used for debugging. /// /// [`rewrite!`]: macro.rewrite.html /// [`Searcher`]: trait.Searcher.html /// [`Applier`]: trait.Applier.html /// [`Condition`]: trait.Condition.html /// [`ConditionalApplier`]: struct.ConditionalApplier.html /// [`Rewrite`]: struct.Rewrite.html /// [`Pattern`]: struct.Pattern.html // TODO display #[derive(Clone)] #[non_exhaustive] pub struct Rewrite<L, N> { name: String, long_name: String, searcher: Rc<dyn Searcher<L, N>>, applier: Rc<dyn Applier<L, N>>, } impl<L: Language, N: Analysis<L>> Rewrite<L, N> { /// Create a new [`Rewrite`]. You typically want to use the /// [`rewrite!`] macro instead. /// /// [`Rewrite`]: struct.Rewrite.html /// [`rewrite!`]: macro.rewrite.html pub fn new( name: impl Into<String>, long_name: impl Into<String>, searcher: impl Searcher<L, N> + 'static, applier: impl Applier<L, N> + 'static, ) -> Self { Self { name: name.into(), long_name: long_name.into(), searcher: Rc::new(searcher), applier: Rc::new(applier), } } /// Returns the name of the rewrite. pub fn name(&self) -> &str { &self.name } /// Returns the long name of the rewrite which should only be used for /// debugging and displaying. pub fn long_name(&self) -> &str { &self.long_name } /// Call [`search`] on the [`Searcher`]. /// /// [`Searcher`]: trait.Searcher.html /// [`search`]: trait.Searcher.html#method.search pub fn search(&self, egraph: &EGraph<L, N>) -> Vec<SearchMatches> { self.searcher.search(egraph) } /// Call [`apply_matches`] on the [`Applier`]. /// /// [`Applier`]: trait.Applier.html /// [`apply_matches`]: trait.Applier.html#method.apply_matches pub fn apply(&self, egraph: &mut EGraph<L, N>, matches: &[SearchMatches]) -> Vec<Id> { self.applier.apply_matches(egraph, matches) } /// This `run` is for testing use only. You should use things /// from the `egg::run` module #[cfg(test)] pub(crate) fn run(&self, egraph: &mut EGraph<L, N>) -> Vec<Id> { let start = instant::Instant::now(); let matches = self.search(egraph); log::debug!("Found rewrite {} {} times", self.name, matches.len()); let ids = self.apply(egraph, &matches); let elapsed = start.elapsed(); log::debug!( "Applied rewrite {} {} times in {}.{:03}", self.name, ids.len(), elapsed.as_secs(), elapsed.subsec_millis() ); egraph.rebuild(); ids } } /// The lefthand side of a [`Rewrite`]. /// /// A [`Searcher`] is something that can search the egraph and find /// matching substititions. /// Right now the only significant [`Searcher`] is [`Pattern`]. /// /// [`Rewrite`]: struct.Rewrite.html /// [`Searcher`]: trait.Searcher.html /// [`Pattern`]: struct.Pattern.html pub trait Searcher<L, N> where L: Language, N: Analysis<L>, { /// Search one eclass, returning None if no matches can be found. /// This should not return a SearchMatches with no substs. fn search_eclass(&self, egraph: &EGraph<L, N>, eclass: Id) -> Option<SearchMatches>; /// Search the whole [`EGraph`], returning a list of all the /// [`SearchMatches`] where something was found. /// This just calls [`search_eclass`] on each eclass. /// /// [`EGraph`]: struct.EGraph.html /// [`search_eclass`]: trait.Searcher.html#tymethod.search_eclass /// [`SearchMatches`]: struct.SearchMatches.html fn search(&self, egraph: &EGraph<L, N>) -> Vec<SearchMatches> { egraph .classes() .filter_map(|e| self.search_eclass(egraph, e.id)) .collect() } } /// The righthand side of a [`Rewrite`]. /// /// An [`Applier`] is anything that can do something with a /// substitition ([`Subst`]). This allows you to implement rewrites /// that determine when and how to respond to a match using custom /// logic, including access to the [`Metadata`] of an [`EClass`]. /// /// Notably, [`Pattern`] implements [`Applier`], which suffices in /// most cases. /// Additionally, `egg` provides [`ConditionalApplier`] to stack /// [`Condition`]s onto an [`Applier`], which in many cases can save /// you from having to implement your own applier. /// /// # Example /// ``` /// use egg::{rewrite as rw, *}; /// /// define_language! { /// enum Math { /// Num(i32), /// "+" = Add([Id; 2]), /// "*" = Mul([Id; 2]), /// Symbol(String), /// } /// } /// /// type EGraph = egg::EGraph<Math, MinSize>; /// /// // Our metadata in this case will be size of the smallest /// // represented expression in the eclass. /// #[derive(Default)] /// struct MinSize; /// impl Analysis<Math> for MinSize { /// type Data = usize; /// fn merge(&self, to: &mut Self::Data, from: Self::Data) -> bool { /// merge_if_different(to, (*to).min(from)) /// } /// fn make(egraph: &EGraph, enode: &Math) -> Self::Data { /// let get_size = |i: Id| egraph[i].data; /// AstSize.cost(enode, get_size) /// } /// } /// /// let rules = &[ /// rw!("commute-add"; "(+ ?a ?b)" => "(+ ?b ?a)"), /// rw!("commute-mul"; "(* ?a ?b)" => "(* ?b ?a)"), /// rw!("add-0"; "(+ ?a 0)" => "?a"), /// rw!("mul-0"; "(* ?a 0)" => "0"), /// rw!("mul-1"; "(* ?a 1)" => "?a"), /// // the rewrite macro parses the rhs as a single token tree, so /// // we wrap it in braces (parens work too). /// rw!("funky"; "(+ ?a (* ?b ?c))" => { Funky { /// a: "?a".parse().unwrap(), /// b: "?b".parse().unwrap(), /// c: "?c".parse().unwrap(), /// }}), /// ]; /// /// #[derive(Debug, Clone, PartialEq, Eq)] /// struct Funky { /// a: Var, /// b: Var, /// c: Var, /// } /// /// impl Applier<Math, MinSize> for Funky { /// fn apply_one(&self, egraph: &mut EGraph, matched_id: Id, subst: &Subst) -> Vec<Id> { /// let a: Id = subst[&self.a]; /// // In a custom Applier, you can inspect the analysis data, /// // which is powerful combination! /// let size_of_a = egraph[a].data; /// if size_of_a > 50 { /// println!("Too big! Not doing anything"); /// vec![] /// } else { /// // we're going to manually add: /// // (+ (+ ?a 0) (* (+ ?b 0) (+ ?c 0))) /// // to be unified with the original: /// // (+ ?a (* ?b ?c )) /// let b: Id = subst[&self.b]; /// let c: Id = subst[&self.c]; /// let zero = egraph.add(Math::Num(0)); /// let a0 = egraph.add(Math::Add([a, zero])); /// let b0 = egraph.add(Math::Add([b, zero])); /// let c0 = egraph.add(Math::Add([c, zero])); /// let b0c0 = egraph.add(Math::Mul([b0, c0])); /// let a0b0c0 = egraph.add(Math::Add([a0, b0c0])); /// // NOTE: we just return the id according to what we /// // want unified with matched_id. The `apply_matches` /// // method actually does the union, _not_ `apply_one`. /// vec![a0b0c0] /// } /// } /// } /// /// let start = "(+ x (* y z))".parse().unwrap(); /// Runner::default().with_expr(&start).run(rules); /// ``` /// [`Pattern`]: struct.Pattern.html /// [`EClass`]: struct.EClass.html /// [`Rewrite`]: struct.Rewrite.html /// [`ConditionalApplier`]: struct.ConditionalApplier.html /// [`Subst`]: struct.Subst.html /// [`Applier`]: trait.Applier.html /// [`Condition`]: trait.Condition.html /// [`Analysis`]: trait.Analysis.html pub trait Applier<L, N> where L: Language, N: Analysis<L>, { /// Apply many substititions. /// /// This method should call [`apply_one`] for each match and then /// unify the results with the matched eclass. /// This should return a list of [`Id`]s where the union actually /// did something. /// /// The default implementation does this and should suffice for /// most use cases. /// /// [`Id`]: type.Id.html /// [`apply_one`]: trait.Applier.html#method.apply_one fn apply_matches(&self, egraph: &mut EGraph<L, N>, matches: &[SearchMatches]) -> Vec<Id> { let mut added = vec![]; for mat in matches { for subst in &mat.substs { let ids = self .apply_one(egraph, mat.eclass, subst) .into_iter() .filter_map(|id| { let (to, did_something) = egraph.union(id, mat.eclass); if did_something { Some(to) } else { None } }); added.extend(ids) } } added } /// Apply a single substitition. /// /// An [`Applier`] should only add things to the egraph here, /// _not_ union them with the id `eclass`. /// That is the responsibility of the [`apply_matches`] method. /// The `eclass` parameter allows the implementer to inspect the /// eclass where the match was found if they need to. /// /// This should return a list of [`Id`]s of things you'd like to /// be unioned with `eclass`. There can be zero, one, or many. /// /// [`Applier`]: trait.Applier.html /// [`Id`]: type.Id.html /// [`apply_matches`]: trait.Applier.html#method.apply_matches fn apply_one(&self, egraph: &mut EGraph<L, N>, eclass: Id, subst: &Subst) -> Vec<Id>; } /// An [`Applier`] that checks a [`Condition`] before applying. /// /// A [`ConditionalApplier`] simply calls [`check`] on the /// [`Condition`] before calling [`apply_one`] on the inner /// [`Applier`]. /// /// See the [`rewrite!`] macro documentation for an example. /// /// [`rewrite!`]: macro.rewrite.html /// [`Applier`]: trait.Applier.html /// [`apply_one`]: trait.Applier.html#method.apply_one /// [`Condition`]: trait.Condition.html /// [`check`]: trait.Condition.html#method.check /// [`ConditionalApplier`]: struct.ConditionalApplier.html #[derive(Clone, Debug)] pub struct ConditionalApplier<C, A> { /// The [`Condition`] to [`check`] before calling [`apply_one`] on /// `applier`. /// /// [`apply_one`]: trait.Applier.html#method.apply_one /// [`Condition`]: trait.Condition.html /// [`check`]: trait.Condition.html#method.check pub condition: C, /// The inner [`Applier`] to call once `condition` passes. /// /// [`Applier`]: trait.Applier.html pub applier: A, } impl<C, A, N, L> Applier<L, N> for ConditionalApplier<C, A> where L: Language, C: Condition<L, N>, A: Applier<L, N>, N: Analysis<L>, { fn apply_one(&self, egraph: &mut EGraph<L, N>, eclass: Id, subst: &Subst) -> Vec<Id> { if self.condition.check(egraph, eclass, subst) { self.applier.apply_one(egraph, eclass, subst) } else { vec![] } } } /// A condition to check in a [`ConditionalApplier`]. /// /// See the [`ConditionalApplier`] docs. /// /// Notably, any function ([`Fn`]) that doesn't mutate other state /// and matches the signature of [`check`] implements [`Condition`]. /// /// [`check`]: trait.Condition.html#method.check /// [`Fn`]: https://doc.rust-lang.org/std/ops/trait.Fn.html /// [`ConditionalApplier`]: struct.ConditionalApplier.html /// [`Condition`]: trait.Condition.html pub trait Condition<L, N> where L: Language, N: Analysis<L>, { /// Check a condition. /// /// `eclass` is the eclass [`Id`] where the match (`subst`) occured. /// If this is true, then the [`ConditionalApplier`] will fire. /// /// [`Id`]: type.Id.html /// [`ConditionalApplier`]: struct.ConditionalApplier.html fn check(&self, egraph: &mut EGraph<L, N>, eclass: Id, subst: &Subst) -> bool; } impl<L, F, N> Condition<L, N> for F where L: Language, N: Analysis<L>, F: Fn(&mut EGraph<L, N>, Id, &Subst) -> bool, { fn check(&self, egraph: &mut EGraph<L, N>, eclass: Id, subst: &Subst) -> bool { self(egraph, eclass, subst) } } /// A [`Condition`] that checks if two terms are equivalent. /// /// This condition adds its two [`Applier`]s to the egraph and passes /// if and only if they are equivalent (in the same eclass). /// /// [`Applier`]: trait.Applier.html /// [`Condition`]: trait.Condition.html pub struct ConditionEqual<A1, A2>(pub A1, pub A2); impl<L, N, A1, A2> Condition<L, N> for ConditionEqual<A1, A2> where L: Language, N: Analysis<L>, A1: Applier<L, N>, A2: Applier<L, N>, { fn check(&self, egraph: &mut EGraph<L, N>, eclass: Id, subst: &Subst) -> bool { let a1 = self.0.apply_one(egraph, eclass, subst); let a2 = self.1.apply_one(egraph, eclass, subst); assert_eq!(a1.len(), 1); assert_eq!(a2.len(), 1); a1[0] == a2[0] } } #[cfg(test)] mod tests { use crate::{StringLang as S, *}; use std::str::FromStr; type EGraph = crate::EGraph<S, ()>; #[test] fn conditional_rewrite() { crate::init_logger(); let mut egraph = EGraph::default(); let x = egraph.add(S::leaf("x")); let y = egraph.add(S::leaf("2")); let mul = egraph.add(S::new("*", vec![x, y])); let true_pat = Pattern::from_str("TRUE").unwrap(); let true_id = egraph.add(S::leaf("TRUE")); let pow2b = Pattern::from_str("(is-power2 ?b)").unwrap(); let mul_to_shift = rewrite!( "mul_to_shift"; "(* ?a ?b)" => "(>> ?a (log2 ?b))" if ConditionEqual(pow2b, true_pat) ); println!("rewrite shouldn't do anything yet"); egraph.rebuild(); let apps = mul_to_shift.run(&mut egraph); assert!(apps.is_empty()); println!("Add the needed equality"); let two_ispow2 = egraph.add(S::new("is-power2", vec![y])); egraph.union(two_ispow2, true_id); println!("Should fire now"); egraph.rebuild(); let apps = mul_to_shift.run(&mut egraph); assert_eq!(apps, vec![egraph.find(mul)]); } #[test] fn fn_rewrite() { crate::init_logger(); let mut egraph = EGraph::default(); let start = RecExpr::from_str("(+ x y)").unwrap(); let goal = RecExpr::from_str("xy").unwrap(); let root = egraph.add_expr(&start); fn get(egraph: &EGraph, id: Id) -> &str { &egraph[id].nodes[0].op } #[derive(Debug)] struct Appender; impl Applier<StringLang, ()> for Appender { fn apply_one(&self, egraph: &mut EGraph, _eclass: Id, subst: &Subst) -> Vec<Id> { let a: Var = "?a".parse().unwrap(); let b: Var = "?b".parse().unwrap(); let a = get(&egraph, subst[&a]); let b = get(&egraph, subst[&b]); let s = format!("{}{}", a, b); vec![egraph.add(S::leaf(&s))] } } let fold_add = rewrite!( "fold_add"; "(+ ?a ?b)" => { Appender } ); egraph.rebuild(); fold_add.run(&mut egraph); assert_eq!(egraph.equivs(&start, &goal), vec![egraph.find(root)]); } }