Parses infix expressions.

Signed-off-by: jmug <u.g.a.mariano@gmail.com>

pkg/parser/parser.go

@@ -30,10 +30,20 @@ func New(l *lexer.Lexer) *Parser {
 		prefixParseFns: map[token.TokenType]prefixParseFn{},
 		infixParseFns:  map[token.TokenType]infixParseFn{},
 	}
+	// Prefix registrations
 	p.registerPrefix(token.IDENT, p.parseIdentifier)
 	p.registerPrefix(token.INT, p.parseIntegerLiteral)
 	p.registerPrefix(token.MINUS, p.parsePrefixExpression)
 	p.registerPrefix(token.BANG, p.parsePrefixExpression)
+	// Infix registrations
+	p.registerInfix(token.PLUS, p.parseInfixExpression)
+	p.registerInfix(token.MINUS, p.parseInfixExpression)
+	p.registerInfix(token.ASTERISK, p.parseInfixExpression)
+	p.registerInfix(token.SLASH, p.parseInfixExpression)
+	p.registerInfix(token.GT, p.parseInfixExpression)
+	p.registerInfix(token.LT, p.parseInfixExpression)
+	p.registerInfix(token.EQ, p.parseInfixExpression)
+	p.registerInfix(token.NOT_EQ, p.parseInfixExpression)
 	// TODO: figure out why this can't be done from `parseProgram`
 	p.nextToken()
 	p.nextToken()
@@ -111,9 +121,16 @@ func (p *Parser) parseExpression(precedence int) ast.Expression {
 		p.noPrefixParseFnError(p.curToken.Type)
 		return nil
 	}
-	leftExpr := prefix()
-	return leftExpr
-
+	curExpr := prefix()
+	for !p.peekTokenIs(token.SEMICOLON) && precedence < p.peekPrecedence() {
+		infix := p.infixParseFns[p.peekToken.Type]
+		if infix == nil {
+			return curExpr
+		}
+		p.nextToken()
+		curExpr = infix(curExpr)
+	}
+	return curExpr
 }
 
 func (p *Parser) parseIdentifier() ast.Expression {
@@ -141,6 +158,18 @@ func (p *Parser) parsePrefixExpression() ast.Expression {
 	return exp
 }
 
+func (p *Parser) parseInfixExpression(left ast.Expression) ast.Expression {
+	exp := &ast.InfixExpression{
+		Token:    p.curToken,
+		Operator: p.curToken.Literal,
+		Left:     left,
+	}
+	precedence := p.curPrecedence()
+	p.nextToken()
+	exp.Right = p.parseExpression(precedence)
+	return exp
+}
+
 func (p *Parser) curTokenIs(typ token.TokenType) bool {
 	return p.curToken.Type == typ
 }

pkg/parser/parser_test.go

@@ -200,6 +200,130 @@ func TestParsingPrefixExpressions(t *testing.T) {
 	}
 }
 
+// parser/parser_test.go
+
+func TestParsingInfixExpressions(t *testing.T) {
+	infixTests := []struct {
+		input      string
+		leftValue  int64
+		operator   string
+		rightValue int64
+	}{
+		{"5 + 5;", 5, "+", 5},
+		{"5 - 5;", 5, "-", 5},
+		{"5 * 5;", 5, "*", 5},
+		{"5 / 5;", 5, "/", 5},
+		{"5 > 5;", 5, ">", 5},
+		{"5 < 5;", 5, "<", 5},
+		{"5 == 5;", 5, "==", 5},
+		{"5 != 5;", 5, "!=", 5},
+	}
+
+	for _, tt := range infixTests {
+		l := lexer.New(tt.input)
+		p := New(l)
+		program := p.ParseProgram()
+		checkParserErrors(t, p)
+
+		if len(program.Statements) != 1 {
+			t.Fatalf("program.Statements does not contain %d statements. got=%d\n",
+				1, len(program.Statements))
+		}
+
+		stmt, ok := program.Statements[0].(*ast.ExpressionStatement)
+		if !ok {
+			t.Fatalf("program.Statements[0] is not ast.ExpressionStatement. got=%T",
+				program.Statements[0])
+		}
+
+		exp, ok := stmt.Expression.(*ast.InfixExpression)
+		if !ok {
+			t.Fatalf("exp is not ast.InfixExpression. got=%T", stmt.Expression)
+		}
+
+		if !testIntegerLiteral(t, exp.Left, tt.leftValue) {
+			return
+		}
+
+		if exp.Operator != tt.operator {
+			t.Fatalf("exp.Operator is not '%s'. got=%s",
+				tt.operator, exp.Operator)
+		}
+
+		if !testIntegerLiteral(t, exp.Right, tt.rightValue) {
+			return
+		}
+	}
+}
+
+func TestOperatorPrecedenceParsing(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected string
+	}{
+		{
+			"-a * b",
+			"((-a) * b)",
+		},
+		{
+			"!-a",
+			"(!(-a))",
+		},
+		{
+			"a + b + c",
+			"((a + b) + c)",
+		},
+		{
+			"a + b - c",
+			"((a + b) - c)",
+		},
+		{
+			"a * b * c",
+			"((a * b) * c)",
+		},
+		{
+			"a * b / c",
+			"((a * b) / c)",
+		},
+		{
+			"a + b / c",
+			"(a + (b / c))",
+		},
+		{
+			"a + b * c + d / e - f",
+			"(((a + (b * c)) + (d / e)) - f)",
+		},
+		{
+			"3 + 4; -5 * 5",
+			"(3 + 4)((-5) * 5)",
+		},
+		{
+			"5 > 4 == 3 < 4",
+			"((5 > 4) == (3 < 4))",
+		},
+		{
+			"5 < 4 != 3 > 4",
+			"((5 < 4) != (3 > 4))",
+		},
+		{
+			"3 + 4 * 5 == 3 * 1 + 4 * 5",
+			"((3 + (4 * 5)) == ((3 * 1) + (4 * 5)))",
+		},
+	}
+
+	for _, tt := range tests {
+		l := lexer.New(tt.input)
+		p := New(l)
+		program := p.ParseProgram()
+		checkParserErrors(t, p)
+
+		actual := program.String()
+		if actual != tt.expected {
+			t.Errorf("expected=%q, got=%q", tt.expected, actual)
+		}
+	}
+}
+
 func testIntegerLiteral(t *testing.T, il ast.Expression, value int64) bool {
 	integ, ok := il.(*ast.IntegerLiteral)
 	if !ok {

pkg/parser/precedence.go

@@ -1,5 +1,9 @@
 package parser
 
+import (
+	"code.jmug.me/jmug/interpreter-in-go/pkg/token"
+)
+
 const (
 	_ int = iota
 	LOWEST
@@ -10,3 +14,28 @@ const (
 	PREFIX      // -X or !X
 	CALL        // myFunction(X)
 )
+
+var precedences = map[token.TokenType]int{
+	token.EQ:       EQUALS,
+	token.NOT_EQ:   EQUALS,
+	token.GT:       LESSGREATER,
+	token.LT:       LESSGREATER,
+	token.PLUS:     SUM,
+	token.MINUS:    SUM,
+	token.ASTERISK: PRODUCT,
+	token.SLASH:    PRODUCT,
+}
+
+func (p *Parser) peekPrecedence() int {
+	if pr, ok := precedences[p.peekToken.Type]; ok {
+		return pr
+	}
+	return LOWEST
+}
+
+func (p *Parser) curPrecedence() int {
+	if pr, ok := precedences[p.curToken.Type]; ok {
+		return pr
+	}
+	return LOWEST
+}