all examples work

src/language.rs

@@ -1,5 +1,5 @@
-use std::{cmp::Ordering, fmt::{self,Display, Formatter}, str::FromStr, sync::LazyLock};
+use std::{cmp::Ordering, fmt::{self,Display, Formatter}, num::ParseIntError, str::FromStr, sync::LazyLock};
-use egg::{define_language, merge_option, rewrite as rw, Analysis, DidMerge, Id, Language, Subst, Var};
+use egg::{define_language, merge_option, rewrite as rw, Analysis, Applier, DidMerge, Id, Language, PatternAst, Subst, Symbol, SymbolLang, Var};
 
 pub type EGraph = egg::EGraph<EquationLanguage, ConstantFold>;
 pub type Rewrite = egg::Rewrite<EquationLanguage, ConstantFold>;
@@ -39,9 +39,19 @@ impl Display for Rational {
 }
 
 impl FromStr for Rational {
-	type Err = std::num::ParseIntError;
+	type Err = String;
-	fn from_str(s: &str) -> Result<Self, Self::Err> {
+	fn from_str(s: &str) -> Result<Self, String> {
-		Ok(Rational { num: s.parse::<i64>()?, denom: 1 })
+		let err = || Err(format!("Couldn't parse rational: {}", s));
+
+		if let Ok(num) = s.parse::<i64>() {
+			Ok(Rational { num, denom: 1 })
+		} else if let Some((snum, sdenom)) = s.split_once('/') {
+			let Ok(num) = snum.parse::<i64>() else { return err(); };
+			let Ok(denom) = sdenom.parse::<u64>() else { return err(); };
+			Ok(Rational { num, denom })
+		} else {
+			err()
+		}
 	}
 }
 
@@ -174,6 +184,39 @@ fn is_const(var: &str) -> impl Fn(&mut EGraph, Id, &Subst) -> bool {
 	}
 }
 
+struct IntegerSqrt {
+	var: Var,
+}
+
+impl Applier<EquationLanguage, ConstantFold> for IntegerSqrt {
+	fn apply_one(&self,
+				 egraph: &mut EGraph,
+				 matched_id: Id,
+				 subst: &Subst,
+				 searcher_pattern: Option<&PatternAst<EquationLanguage>>,
+				 rule_name: Symbol)
+				 -> Vec<Id> {
+		let var_id = subst[self.var];
+
+		if let Some(value) = &egraph[var_id].data {
+			if value.denom == 1 && value.num >= 0 {
+				// isqrt is nightly only, so we just do this, adding 0.1 against rounding errors
+				let sq = (f64::sqrt(value.num as f64) + 0.1) as i64;
+				if value.num == sq*sq {
+//					println!("square root of integer {} is {}", value.num, sq);
+
+					let sq_id = egraph.add(EquationLanguage::Num(Rational { num: sq, denom: 1 }));
+					egraph.union(matched_id, sq_id);
+
+					return vec![matched_id, sq_id];
+				}
+			}
+		}
+
+		vec![]
+	}
+}
+
 pub static RULES: LazyLock<Vec<Rewrite>> = LazyLock::new(||vec![
 	rw!("commute-add"; "(+ ?x ?y)" => "(+ ?y ?x)"),
 	rw!("commute-mul"; "(* ?x ?y)" => "(* ?y ?x)"),
@@ -185,6 +228,8 @@ pub static RULES: LazyLock<Vec<Rewrite>> = LazyLock::new(||vec![
 	rw!("mul-0"; "(* ?x 0)" => "0"),
 	rw!("mul-1"; "(* ?x 1)" => "?x"),
 
+	rw!("0-sub"; "(- 0 ?x)" => "(- ?x)"),
+
 	rw!("add-sub"; "(+ ?x (* (-1) ?x))" => "0"),
 	// division by zero shouldn't happen unless input is invalid
 	rw!("mul-div"; "(* ?x (rec ?x))" => "1" if is_nonzero_const("?y")),
@@ -202,7 +247,7 @@ pub static RULES: LazyLock<Vec<Rewrite>> = LazyLock::new(||vec![
 
 	rw!("factor_poly"; "(+ (* x ?x) ?y)" => "(* ?x (+ x (* ?y (rec ?x))))" if is_nonzero_const("?x")),
 
-//	rw!("integer_sqrt"; "(^ ?x (1/2))" => {} if is_const("?x")),
+	rw!("integer_sqrt"; "(^ ?x (/ 1 2))" => { IntegerSqrt { var: "?x".parse().unwrap() } } if is_const("?x")),
 ]);
 
 pub struct PlusTimesCostFn;