new(rs): fully by-hand expression simplification (#273)

* testing: filter out nAn-looking things in proptests

* fix: some more rules, big test commented out

* fix: use velcro, simplify and add some rules

* fix: rename some rules

* fix: remove pathological test case; simplify ruleset

* fix: typo

* new(rs): combine by hand & egg to simplify expressions

* feat: remove egg, rely solely on by_hand

* fix: unused dep

* fix: debug

* fix: clippy

* fix: un-remove hash utility

* wip: still getting syntax errors on the affine case

* fix: fewer references and clones

* fix: get affine working

* fix: π => 3.1415926535897932384626…

* fix: various tidyings and comments

* doc: justify LIMIT = 1

* fix: respond to PR review comments

* fix: some other opportunities for simplification

* fix: responding to PR review comments

* fix: test coverage

* fix: make private something that no longer needs pub(crate)

* fix: responding to PR comments

* fix: Commentary tweaks per review comments

* fix: simplify exponentiations of numbers or π

* fix: remove erroneous subtraction rule

* fix: add simple double subtraction test to protect against previous bad rule

quil-rs/Cargo.toml

@@ -12,7 +12,6 @@ categories = ["parser-implementations", "science", "compilers", "emulators"]
 [dependencies]
 approx = { version = "0.5.1", features = ["num-complex"] }
 dot-writer = { version = "0.1.2", optional = true }
-egg = { version = "0.9.4", features = ["deterministic"] }
 indexmap = "1.6.1"
 itertools = "0.11.0"
 lexical = "6.1.1"
@@ -40,7 +39,7 @@ rstest = "0.18.1"
 # These are described in the crate README.md
 [features]
 graphviz-dot = ["dot-writer"]
-wasm-bindgen = ["egg/wasm-bindgen"]
+wasm-bindgen = []
 
 [[bench]]
 name = "parser"

quil-rs/src/expression/mod.rs

@@ -259,11 +259,7 @@ impl Expression {
             Expression::PiConstant => {
                 *self = Expression::Number(Complex64::from(PI));
             }
-            _ => {
-                if let Ok(simpler) = simplification::run(self) {
-                    *self = simpler;
-                }
-            }
+            _ => *self = simplification::run(self),
         }
     }
 
@@ -666,11 +662,19 @@ impl fmt::Display for InfixOperator {
 #[allow(clippy::arc_with_non_send_sync)]
 mod tests {
     use super::*;
-    use crate::hash::hash_to_u64;
     use crate::reserved::ReservedToken;
     use proptest::prelude::*;
+    use std::collections::hash_map::DefaultHasher;
     use std::collections::HashSet;
 
+    /// Hash value helper: turn a hashable thing into a u64.
+    #[inline]
+    fn hash_to_u64<T: Hash>(t: &T) -> u64 {
+        let mut s = DefaultHasher::new();
+        t.hash(&mut s);
+        s.finish()
+    }
+
     #[test]
     fn simplify_and_evaluate() {
         use Expression::*;
@@ -790,7 +794,7 @@ mod tests {
     // Better behaved than the auto-derived version for names
     fn arb_name() -> impl Strategy<Value = String> {
         r"[a-z][a-zA-Z0-9]{1,10}".prop_filter("Exclude reserved tokens", |t| {
-            ReservedToken::from_str(t).is_err()
+            ReservedToken::from_str(t).is_err() && !t.to_lowercase().starts_with("nan")
         })
     }
 
@@ -835,12 +839,10 @@ mod tests {
                             right: Box::new(r)
                         })
                     ),
-                    (any::<PrefixOperator>(), expr).prop_map(|(operator, e)| Prefix(
-                        PrefixExpression {
-                            operator,
-                            expression: Box::new(e)
-                        }
-                    ))
+                    (expr).prop_map(|e| Prefix(PrefixExpression {
+                        operator: PrefixOperator::Minus,
+                        expression: Box::new(e)
+                    }))
                 ]
             },
         )