Nested ternary expressions are illegal

parser/parser.go

@@ -97,6 +97,11 @@ type Parser struct {
 	// postfixParseFns holds a map of parsing methods for
 	// postfix-based syntax.
 	postfixParseFns map[token.Type]postfixParseFn
+
+	// are we inside a ternary expression?
+	//
+	// Nested ternary expressions are illegal :)
+	tern bool
 }
 
 // New returns our new parser-object.
@@ -387,6 +392,16 @@ func (p *Parser) parseInfixExpression(left ast.Expression) ast.Expression {
 
 // parseTernaryExpression parses a ternary expression
 func (p *Parser) parseTernaryExpression(condition ast.Expression) ast.Expression {
+
+	if p.tern {
+		msg := fmt.Sprintf("nested ternary expressions are illegal, around line %d", p.l.GetLine())
+		p.errors = append(p.errors, msg)
+		return nil
+	}
+
+	p.tern = true
+	defer func() { p.tern = false }()
+
 	expression := &ast.TernaryExpression{
 		Token:     p.curToken,
 		Condition: condition,
@@ -403,6 +418,7 @@ func (p *Parser) parseTernaryExpression(condition ast.Expression) ast.Expression
 	p.nextToken()
 	expression.IfFalse = p.parseExpression(precedence)
 
+	p.tern = false
 	return expression
 }