Tweak precedence handling in the parser

board-shared/src/expr.rs

@@ -284,4 +284,18 @@ mod tests {
         ];
         assert!(!is_valid_guess_of_tokens(&tokens));
     }
+
+    #[test]
+    fn is_valid_guess_of_tiles_precedence() {
+        let tokens = vec![
+            Token::NumberLiteral(5),
+            Token::Operator(Operator::Add),
+            Token::NumberLiteral(-2),
+            Token::Operator(Operator::Multiply),
+            Token::NumberLiteral(3),
+            Token::Equals,
+            Token::NumberLiteral(-1),
+        ];
+        assert!(is_valid_guess_of_tokens(&tokens));
+    }
 }

board-shared/src/parser.rs

@@ -30,53 +30,60 @@ pub fn parse(tokens: &[Token]) -> Result<Expressions, ()> {
     let mut tokens = tokens.iter().peekable();
     let mut expressions = Vec::new();
     while tokens.peek().is_some() {
-        expressions.push(parse_expression(&mut tokens)?);
+        expressions.push(parse_term(&mut tokens)?);
         tokens.next();
     }
     Ok(expressions)
 }
 
-fn parse_expression<'a>(
+fn parse_primary<'a>(
     tokens: &mut Peekable<impl Iterator<Item = &'a Token>>,
 ) -> Result<Expression, ()> {
-    let mut left = parse_term(tokens)?;
-    while let Some(Token::Operator(operator)) = tokens.peek() {
-        let operator = *operator;
+    if let Some(Token::NumberLiteral(value)) = tokens.peek() {
         tokens.next();
-        let right = parse_term(tokens)?;
-        left = Expression::Binary(operator, Box::new(left), Box::new(right));
+        Ok(Expression::Digit(*value))
+    } else if let Some(Token::LeftParen) = tokens.peek() {
+        tokens.next();
+        let expr = parse_term(tokens)?;
+        if let Some(Token::RightParen) = tokens.peek() {
+            tokens.next();
+            Ok(Expression::Parentheses(Box::new(expr)))
+        } else {
+            Err(())
+        }
+    } else {
+        Err(())
     }
-    Ok(left)
 }
 
 fn parse_term<'a>(
     tokens: &mut Peekable<impl Iterator<Item = &'a Token>>,
 ) -> Result<Expression, ()> {
-    let mut left = parse_unary(tokens)?;
+    let mut expr = parse_factor(tokens)?;
     while let Some(Token::Operator(operator)) = tokens.peek() {
-        let operator = *operator;
+        if !matches!(operator, Operator::Add | Operator::Subtract) {
+            break;
+        }
         tokens.next();
-        let right = parse_unary(tokens)?;
-        left = Expression::Binary(operator, Box::new(left), Box::new(right));
+        let right = parse_factor(tokens)?;
+        expr = Expression::Binary(*operator, Box::new(expr), Box::new(right));
     }
-    Ok(left)
+    Ok(expr)
 }
 
 fn parse_factor<'a>(
     tokens: &mut Peekable<impl Iterator<Item = &'a Token>>,
 ) -> Result<Expression, ()> {
-    match tokens.next() {
-        Some(Token::NumberLiteral(value)) => Ok(Expression::Digit(*value)),
-        Some(Token::LeftParen) => {
-            let expression = parse_expression(tokens)?;
-            if let Some(Token::RightParen) = tokens.next() {
-                Ok(Expression::Parentheses(Box::new(expression)))
-            } else {
-                Err(())
-            }
+    let mut expr = parse_unary(tokens)?;
+    while let Some(Token::Operator(operator)) = tokens.peek() {
+        if !matches!(operator, Operator::Multiply | Operator::Divide) {
+            break;
         }
-        _ => Err(()),
+        tokens.next();
+        let right = parse_unary(tokens)?;
+        expr = Expression::Binary(*operator, Box::new(expr), Box::new(right));
     }
+    Ok(expr)
 }
 
 fn parse_unary<'a>(
@@ -87,7 +94,7 @@ fn parse_unary<'a>(
         let expression = parse_unary(tokens)?;
         Ok(Expression::Unary(Operator::Subtract, Box::new(expression)))
     } else {
-        parse_factor(tokens)
+        parse_primary(tokens)
     }
 }
 
@@ -108,13 +115,37 @@ mod tests {
         assert_eq!(
             expression,
             vec![Expression::Binary(
-                Operator::Multiply,
+                Operator::Add,
+                Box::new(Expression::Digit(1)),
                 Box::new(Expression::Binary(
-                    Operator::Add,
-                    Box::new(Expression::Digit(1)),
+                    Operator::Multiply,
                     Box::new(Expression::Digit(2)),
+                    Box::new(Expression::Digit(3)),
                 )),
-                Box::new(Expression::Digit(3)),
+            )],
+        );
+    }
+
+    #[test]
+    fn test_parse_reverse() {
+        let tokens = vec![
+            Token::NumberLiteral(2),
+            Token::Operator(Operator::Multiply),
+            Token::NumberLiteral(3),
+            Token::Operator(Operator::Add),
+            Token::NumberLiteral(1),
+        ];
+        let expression = parse(&tokens).unwrap();
+        assert_eq!(
+            expression,
+            vec![Expression::Binary(
+                Operator::Add,
+                Box::new(Expression::Binary(
+                    Operator::Multiply,
+                    Box::new(Expression::Digit(2)),
+                    Box::new(Expression::Digit(3)),
+                )),
+                Box::new(Expression::Digit(1)),
             )],
         );
     }