improve Precedence error message

compiler/parse/src/ast.rs

@@ -165,7 +165,7 @@ pub enum Expr<'a> {
     MalformedClosure,
     // Both operators were non-associative, e.g. (True == False == False).
     // We should tell the author to disambiguate by grouping them with parens.
-    PrecedenceConflict(Loc<BinOp>, Loc<BinOp>, &'a Loc<Expr<'a>>),
+    PrecedenceConflict(Region, Loc<BinOp>, Loc<BinOp>, &'a Loc<Expr<'a>>),
 }
 
 #[derive(Debug, Clone, PartialEq)]

compiler/parse/src/expr.rs

@@ -323,7 +323,7 @@ fn expr_to_pattern<'a>(arena: &'a Bump, expr: &Expr<'a>) -> Result<Pattern<'a>,
         | Expr::If(_, _, _)
         | Expr::When(_, _)
         | Expr::MalformedClosure
-        | Expr::PrecedenceConflict(_, _, _)
+        | Expr::PrecedenceConflict(_, _, _, _)
         | Expr::Record {
             update: Some(_), ..
         }

compiler/parse/src/operator.rs

@@ -1,5 +1,6 @@
 use self::BinOp::*;
 use std::cmp::Ordering;
+use std::fmt;
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum CalledVia {
@@ -109,3 +110,29 @@ impl Ord for BinOp {
         self.precedence().cmp(&other.precedence())
     }
 }
+
+impl std::fmt::Display for BinOp {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let as_str = match self {
+            Caret => "^",
+            Star => "*",
+            Slash => "/",
+            DoubleSlash => "//",
+            Percent => "%",
+            DoublePercent => "%%",
+            Plus => "+",
+            Minus => "-",
+            Equals => "==",
+            NotEquals => "!=",
+            LessThan => "<",
+            GreaterThan => ">",
+            LessThanOrEq => "<=",
+            GreaterThanOrEq => ">=",
+            And => "&&",
+            Or => "||",
+            Pizza => "|>",
+        };
+
+        write!(f, "({})", as_str)
+    }
+}