private Ast.IExpression ParseIfExpression()
{
var expression = new Ast.IfExpression
{
Token = _curToken
};
NextToken();
expression.Condition = ParseExpression(Precedence.Lowest);
if (!ExpectPeek(TokenType.Lbrace))
{
return(null);
}
expression.Consequence = ParseBlockStatement();
if (PeekTokenIs(TokenType.Else))
{
NextToken();
if (PeekTokenIs(TokenType.If))
{
NextToken();
expression.Alternative = new Ast.BlockStatement
{
Statements = new List <Ast.IStatement>
{
new Ast.ExpressionStatement
{
Expression = ParseIfExpression()
}
}
};
return(expression);
}
if (!ExpectPeek(TokenType.Lbrace))
{
return(null);
}
expression.Alternative = ParseBlockStatement();
}
return(expression);
}
private static IObject EvalIfExpression(Ast.IfExpression ie, Environment env)
{
var condition = Eval(ie.Condition, env);
if (IsError(condition))
{
return(condition);
}
if (IsTruthy(condition))
{
return(Eval(ie.Consequence, env));
}
else if (ie.Alternative != null)
{
return(Eval(ie.Alternative, env));
}
return(Null);
}