Merge pull request #2 from kamilturek/grouped-expressions

Grouped Expressions

README.md

@@ -45,3 +45,24 @@ let y = 5 < 5;
 let z = 5 == 5;
 let v = 5 != 5;
 ```
+
+### Operator Precedence
+
+The following table shows the operator precedence in Monkey, from lowest to highest:
+
+| Precedence Level | Operators       | Description                |
+|------------------|-----------------|----------------------------|
+| 6 (Highest)      | Function calls  | Function calls             |
+| 5                | Prefix `-`, `!` | Unary operations           |
+| 4                | `*`, `/`        | Multiplication and Division|
+| 3                | `+`, `-`        | Addition and Subtraction   |
+| 2                | `<`, `>`        | Comparison                 |
+| 1 (Lowest)       | `==`, `!=`      | Equality                   |
+
+### Grouped Expressions
+
+You can use parentheses to influence the order of executing arithmetic operations.
+
+```
+let x = (2 / (5 + 5));
+```

parser/parser.go

@@ -60,6 +60,7 @@ func NewParser(l *lexer.Lexer) *Parser {
 	p.registerPrefix(token.FALSE, p.parseBooleanLiteral)
 	p.registerPrefix(token.BANG, p.parsePrefixExpression)
 	p.registerPrefix(token.MINUS, p.parsePrefixExpression)
+	p.registerPrefix(token.LPAREN, p.parseGroupedExpression)
 
 	p.registerInfix(token.PLUS, p.parseInfixExpression)
 	p.registerInfix(token.MINUS, p.parseInfixExpression)
@@ -259,6 +260,18 @@ func (p *Parser) parseInfixExpression(left ast.Expression) ast.Expression {
 	return expression
 }
 
+func (p *Parser) parseGroupedExpression() ast.Expression {
+	p.nextToken()
+
+	exp := p.parseExpression(LOWEST)
+
+	if !p.exceptPeek(token.RPAREN) {
+		return nil
+	}
+
+	return exp
+}
+
 func (p *Parser) parseIdentifier() ast.Expression {
 	return &ast.Identifier{Token: p.curToken, Value: p.curToken.Literal}
 }

parser/parser_test.go

@@ -435,6 +435,26 @@ func TestOperatorPrecedenceParsing(t *testing.T) {
 			"3 < 5 == true",
 			"((3 < 5) == true)",
 		},
+		{
+			"1 + (2 + 3) + 4",
+			"((1 + (2 + 3)) + 4)",
+		},
+		{
+			"(5 + 5) * 2",
+			"((5 + 5) * 2)",
+		},
+		{
+			"2 / (5 + 5)",
+			"(2 / (5 + 5))",
+		},
+		{
+			"-(5 + 5)",
+			"(-(5 + 5))",
+		},
+		{
+			"!(true == true)",
+			"(!(true == true))",
+		},
 	}
 
 	for _, tt := range tests {