Change assignment into expressions

parser/parser.go

@@ -11,6 +11,7 @@ import (
 const (
 	_ int = iota
 	LOWEST
+	ASSIGN      // =
 	EQUALS      // ==
 	LESSGREATER // > or <
 	SUM         // +
@@ -21,6 +22,7 @@ const (
 )
 
 var precedences = map[token.TokenType]int{
+	token.ASSIGN:   ASSIGN,
 	token.EQ:       EQUALS,
 	token.NOT_EQ:   EQUALS,
 	token.LT:       LESSGREATER,
@@ -86,6 +88,7 @@ func New(l *lexer.Lexer) *Parser {
 	p.registerInfix(token.GTE, p.parseInfixExpression)
 	p.registerInfix(token.LPAREN, p.parseCallExpression)
 	p.registerInfix(token.LBRACKET, p.parseIndexExpression)
+	p.registerInfix(token.ASSIGN, p.parseAssignmentExpression)
 
 	// Read two tokens, so curToken and peekToken are both set
 	p.nextToken()
@@ -153,10 +156,6 @@ func (p *Parser) ParseProgram() *ast.Program {
 }
 
 func (p *Parser) parseStatement() ast.Statement {
-	if p.peekToken.Type == token.ASSIGN {
-		return p.parseAssignmentStatement()
-	}
-
 	switch p.curToken.Type {
 	case token.COMMENT:
 		return p.parseComment()
@@ -347,6 +346,18 @@ func (p *Parser) parseIfExpression() ast.Expression {
 	if p.peekTokenIs(token.ELSE) {
 		p.nextToken()
 
+		if p.peekTokenIs(token.IF) {
+			p.nextToken()
+			expression.Alternative = &ast.BlockStatement{
+				Statements: []ast.Statement{
+					&ast.ExpressionStatement{
+						Expression: p.parseIfExpression(),
+					},
+				},
+			}
+			return expression
+		}
+
 		if !p.expectPeek(token.LBRACE) {
 			return nil
 		}
@@ -534,20 +545,22 @@ func (p *Parser) parseWhileExpression() ast.Expression {
 	return expression
 }
 
-func (p *Parser) parseAssignmentStatement() ast.Statement {
-	stmt := &ast.AssignmentStatement{Token: p.peekToken}
-	stmt.Name = &ast.Identifier{Token: p.curToken, Value: p.curToken.Literal}
-
-	p.nextToken()
-	p.nextToken()
-
-	stmt.Value = p.parseExpression(LOWEST)
-
-	if p.peekTokenIs(token.SEMICOLON) {
-		p.nextToken()
+func (p *Parser) parseAssignmentExpression(exp ast.Expression) ast.Expression {
+	switch node := exp.(type) {
+	case *ast.Identifier, *ast.IndexExpression:
+	default:
+		msg := fmt.Sprintf("expected identifier or index expression on left but got %T %#v", node, exp)
+		p.errors = append(p.errors, msg)
+		return nil
 	}
 
-	return stmt
+	ae := &ast.AssignmentExpression{Token: p.curToken, Left: exp}
+
+	p.nextToken()
+
+	ae.Value = p.parseExpression(LOWEST)
+
+	return ae
 }
 
 func (p *Parser) parseComment() ast.Statement {