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use pattern::apply_pat;
use std::fmt::{self, Debug, Display};
use std::sync::Arc;
use crate::*;
/// A rewrite that searches for the lefthand side and applies the righthand side.
///
/// The [`rewrite!`] macro 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.
///
#[derive(Clone)]
#[non_exhaustive]
pub struct Rewrite<L, N> {
/// The name of the rewrite.
pub name: Symbol,
/// The searcher (left-hand side) of the rewrite.
pub searcher: Arc<dyn Searcher<L, N> + Sync + Send>,
/// The applier (right-hand side) of the rewrite.
pub applier: Arc<dyn Applier<L, N> + Sync + Send>,
}
impl<L, N> Debug for Rewrite<L, N>
where
L: Language + Display + 'static,
N: Analysis<L> + 'static,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let mut d = f.debug_struct("Rewrite");
d.field("name", &self.name);
// if let Some(pat) = Any::downcast_ref::<dyn Pattern<L>>(&self.searcher) {
if let Some(pat) = self.searcher.get_pattern_ast() {
d.field("searcher", &DisplayAsDebug(pat));
} else {
d.field("searcher", &"<< searcher >>");
}
if let Some(pat) = self.applier.get_pattern_ast() {
d.field("applier", &DisplayAsDebug(pat));
} else {
d.field("applier", &"<< applier >>");
}
d.finish()
}
}
impl<L: Language, N: Analysis<L>> Rewrite<L, N> {
/// Create a new [`Rewrite`]. You typically want to use the
/// [`rewrite!`] macro instead.
///
pub fn new(
name: impl Into<Symbol>,
searcher: impl Searcher<L, N> + Send + Sync + 'static,
applier: impl Applier<L, N> + Send + Sync + 'static,
) -> Result<Self, String> {
let name = name.into();
let searcher = Arc::new(searcher);
let applier = Arc::new(applier);
let bound_vars = searcher.vars();
for v in applier.vars() {
if !bound_vars.contains(&v) {
return Err(format!("Rewrite {} refers to unbound var {}", name, v));
}
}
Ok(Self {
name,
searcher,
applier,
})
}
/// Call [`search`] on the [`Searcher`].
///
/// [`search`]: Searcher::search()
pub fn search(&self, egraph: &EGraph<L, N>) -> Vec<SearchMatches<L>> {
self.searcher.search(egraph)
}
/// Call [`search_with_limit`] on the [`Searcher`].
///
/// [`search_with_limit`]: Searcher::search_with_limit()
pub fn search_with_limit(&self, egraph: &EGraph<L, N>, limit: usize) -> Vec<SearchMatches<L>> {
self.searcher.search_with_limit(egraph, limit)
}
/// Call [`apply_matches`] on the [`Applier`].
///
/// [`apply_matches`]: Applier::apply_matches()
pub fn apply(&self, egraph: &mut EGraph<L, N>, matches: &[SearchMatches<L>]) -> Vec<Id> {
self.applier.apply_matches(egraph, matches, self.name)
}
/// 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 = crate::util::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
}
}
/// Searches the given list of e-classes with a limit.
pub(crate) fn search_eclasses_with_limit<'a, I, S, L, N>(
searcher: &'a S,
egraph: &EGraph<L, N>,
eclasses: I,
mut limit: usize,
) -> Vec<SearchMatches<'a, L>>
where
L: Language,
N: Analysis<L>,
S: Searcher<L, N> + ?Sized,
I: IntoIterator<Item = Id>,
{
let mut ms = vec![];
for eclass in eclasses {
if limit == 0 {
break;
}
match searcher.search_eclass_with_limit(egraph, eclass, limit) {
None => continue,
Some(m) => {
let len = m.substs.len();
assert!(len <= limit);
limit -= len;
ms.push(m);
}
}
}
ms
}
/// The lefthand side of a [`Rewrite`].
///
/// A [`Searcher`] is something that can search the egraph and find
/// matching substitutions.
/// Right now the only significant [`Searcher`] is [`Pattern`].
///
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<L>> {
self.search_eclass_with_limit(egraph, eclass, usize::MAX)
}
/// Similar to [`search_eclass`], but return at most `limit` many matches.
///
/// Implementation of [`Searcher`] should implement
/// [`search_eclass_with_limit`].
///
/// [`search_eclass`]: Searcher::search_eclass
/// [`search_eclass_with_limit`]: Searcher::search_eclass_with_limit
fn search_eclass_with_limit(
&self,
egraph: &EGraph<L, N>,
eclass: Id,
limit: usize,
) -> Option<SearchMatches<L>>;
/// Search the whole [`EGraph`], returning a list of all the
/// [`SearchMatches`] where something was found.
/// This just calls [`search_eclass`] on each eclass.
///
/// [`search_eclass`]: Searcher::search_eclass
fn search(&self, egraph: &EGraph<L, N>) -> Vec<SearchMatches<L>> {
egraph
.classes()
.filter_map(|e| self.search_eclass(egraph, e.id))
.collect()
}
/// Similar to [`search`], but return at most `limit` many matches.
///
/// [`search`]: Searcher::search
fn search_with_limit(&self, egraph: &EGraph<L, N>, limit: usize) -> Vec<SearchMatches<L>> {
search_eclasses_with_limit(self, egraph, egraph.classes().map(|e| e.id), limit)
}
/// Returns the number of matches in the e-graph
fn n_matches(&self, egraph: &EGraph<L, N>) -> usize {
self.search(egraph).iter().map(|m| m.substs.len()).sum()
}
/// For patterns, return the ast directly as a reference
fn get_pattern_ast(&self) -> Option<&PatternAst<L>> {
None
}
/// Returns a list of the variables bound by this Searcher
fn vars(&self) -> Vec<Var>;
}
/// The righthand side of a [`Rewrite`].
///
/// An [`Applier`] is anything that can do something with a
/// substitution ([`Subst`]). This allows you to implement rewrites
/// that determine when and how to respond to a match using custom
/// logic, including access to the [`Analysis`] data 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, *};
/// use std::sync::Arc;
///
/// define_language! {
/// enum Math {
/// Num(i32),
/// "+" = Add([Id; 2]),
/// "*" = Mul([Id; 2]),
/// Symbol(Symbol),
/// }
/// }
///
/// 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(&mut self, to: &mut Self::Data, from: Self::Data) -> DidMerge {
/// merge_min(to, 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(),
/// ast: "(+ (+ ?a 0) (* (+ ?b 0) (+ ?c 0)))".parse().unwrap(),
/// }}),
/// ];
///
/// #[derive(Debug, Clone, PartialEq, Eq)]
/// struct Funky {
/// a: Var,
/// b: Var,
/// c: Var,
/// ast: PatternAst<Math>,
/// }
///
/// impl Applier<Math, MinSize> for Funky {
///
/// fn apply_one(&self, egraph: &mut EGraph, matched_id: Id, subst: &Subst, searcher_pattern: Option<&PatternAst<Math>>, rule_name: Symbol) -> 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]));
/// // Don't forget to union the new node with the matched node!
/// if egraph.union(matched_id, a0b0c0) {
/// vec![a0b0c0]
/// } else {
/// vec![]
/// }
/// }
/// }
/// }
///
/// let start = "(+ x (* y z))".parse().unwrap();
/// Runner::default().with_expr(&start).run(rules);
/// ```
pub trait Applier<L, N>
where
L: Language,
N: Analysis<L>,
{
/// Apply many substitutions.
///
/// This method should call [`apply_one`] for each match.
///
/// It returns the ids resulting from the calls to [`apply_one`].
/// The default implementation does this and should suffice for
/// most use cases.
///
/// [`apply_one`]: Applier::apply_one()
fn apply_matches(
&self,
egraph: &mut EGraph<L, N>,
matches: &[SearchMatches<L>],
rule_name: Symbol,
) -> Vec<Id> {
let mut added = vec![];
for mat in matches {
let ast = if egraph.are_explanations_enabled() {
mat.ast.as_ref().map(|cow| cow.as_ref())
} else {
None
};
for subst in &mat.substs {
let ids = self.apply_one(egraph, mat.eclass, subst, ast, rule_name);
added.extend(ids)
}
}
added
}
/// For patterns, get the ast directly as a reference.
fn get_pattern_ast(&self) -> Option<&PatternAst<L>> {
None
}
/// Apply a single substitution.
///
/// An [`Applier`] should add things and union them with `eclass`.
/// Appliers can also inspect the eclass if necessary using the
/// `eclass` parameter.
///
/// This should return a list of [`Id`]s of eclasses that
/// were changed. There can be zero, one, or many.
/// When explanations mode is enabled, a [`PatternAst`] for
/// the searcher is provided.
///
/// [`apply_matches`]: Applier::apply_matches()
fn apply_one(
&self,
egraph: &mut EGraph<L, N>,
eclass: Id,
subst: &Subst,
searcher_ast: Option<&PatternAst<L>>,
rule_name: Symbol,
) -> Vec<Id>;
/// Returns a list of variables that this Applier assumes are bound.
///
/// `egg` will check that the corresponding `Searcher` binds those
/// variables.
/// By default this return an empty `Vec`, which basically turns off the
/// checking.
fn vars(&self) -> Vec<Var> {
vec![]
}
}
/// 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.
///
/// [`apply_one`]: Applier::apply_one()
/// [`check`]: Condition::check()
#[derive(Clone, Debug)]
pub struct ConditionalApplier<C, A> {
/// The [`Condition`] to [`check`] before calling [`apply_one`] on
/// `applier`.
///
/// [`apply_one`]: Applier::apply_one()
/// [`check`]: Condition::check()
pub condition: C,
/// The inner [`Applier`] to call once `condition` passes.
///
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 get_pattern_ast(&self) -> Option<&PatternAst<L>> {
self.applier.get_pattern_ast()
}
fn apply_one(
&self,
egraph: &mut EGraph<L, N>,
eclass: Id,
subst: &Subst,
searcher_ast: Option<&PatternAst<L>>,
rule_name: Symbol,
) -> Vec<Id> {
if self.condition.check(egraph, eclass, subst) {
self.applier
.apply_one(egraph, eclass, subst, searcher_ast, rule_name)
} else {
vec![]
}
}
fn vars(&self) -> Vec<Var> {
let mut vars = self.applier.vars();
vars.extend(self.condition.vars());
vars
}
}
/// 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`]: Condition::check()
/// [`Fn`]: std::ops::Fn
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.
///
fn check(&self, egraph: &mut EGraph<L, N>, eclass: Id, subst: &Subst) -> bool;
/// Returns a list of variables that this Condition assumes are bound.
///
/// `egg` will check that the corresponding `Searcher` binds those
/// variables.
/// By default this return an empty `Vec`, which basically turns off the
/// checking.
fn vars(&self) -> Vec<Var> {
vec![]
}
}
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 [`Pattern`] to the egraph and passes
/// if and only if they are equivalent (in the same eclass).
///
#[derive(Debug)]
pub struct ConditionEqual<L> {
p1: Pattern<L>,
p2: Pattern<L>,
}
impl<L: Language> ConditionEqual<L> {
/// Create a new [`ConditionEqual`] condition given two patterns.
pub fn new(p1: Pattern<L>, p2: Pattern<L>) -> Self {
ConditionEqual { p1, p2 }
}
}
impl<L: FromOp> ConditionEqual<L> {
/// Create a ConditionEqual by parsing two pattern strings.
///
/// This panics if the parsing fails.
pub fn parse(a1: &str, a2: &str) -> Self {
Self {
p1: a1.parse().unwrap(),
p2: a2.parse().unwrap(),
}
}
}
impl<L, N> Condition<L, N> for ConditionEqual<L>
where
L: Language,
N: Analysis<L>,
{
fn check(&self, egraph: &mut EGraph<L, N>, _eclass: Id, subst: &Subst) -> bool {
let mut id_buf_1 = vec![0.into(); self.p1.ast.as_ref().len()];
let mut id_buf_2 = vec![0.into(); self.p2.ast.as_ref().len()];
let a1 = apply_pat(&mut id_buf_1, self.p1.ast.as_ref(), egraph, subst);
let a2 = apply_pat(&mut id_buf_2, self.p2.ast.as_ref(), egraph, subst);
a1 == a2
}
fn vars(&self) -> Vec<Var> {
let mut vars = self.p1.vars();
vars.extend(self.p2.vars());
vars
}
}
#[cfg(test)]
mod tests {
use crate::{SymbolLang 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();
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::new(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");
egraph.union_instantiations(
&"(is-power2 2)".parse().unwrap(),
&"TRUE".parse().unwrap(),
&Default::default(),
"direct-union".to_string(),
);
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) -> Symbol {
egraph[id].nodes[0].op
}
#[derive(Debug)]
struct Appender {
_rhs: PatternAst<S>,
}
impl Applier<SymbolLang, ()> for Appender {
fn apply_one(
&self,
egraph: &mut EGraph,
eclass: Id,
subst: &Subst,
searcher_ast: Option<&PatternAst<SymbolLang>>,
rule_name: Symbol,
) -> 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);
if let Some(ast) = searcher_ast {
let (id, did_something) = egraph.union_instantiations(
ast,
&PatternAst::from_str(&s).unwrap(),
subst,
rule_name,
);
if did_something {
vec![id]
} else {
vec![]
}
} else {
let added = egraph.add(S::leaf(&s));
if egraph.union(added, eclass) {
vec![eclass]
} else {
vec![]
}
}
}
}
let fold_add = rewrite!(
"fold_add"; "(+ ?a ?b)" => { Appender { _rhs: "?a".parse().unwrap()}}
);
egraph.rebuild();
fold_add.run(&mut egraph);
assert_eq!(egraph.equivs(&start, &goal), vec![egraph.find(root)]);
}
}