private static IMonkeyObject EvalIfExpression(IfExpression ie, MonkeyEnvironment 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);
}
private IExpression ParseIfExpression()
{
var expression = new IfExpression {
Token = _curToken
};
if (!ExpectPeek(TokenType.LParen))
{
return(null);
}
NextToken();
expression.Condition = ParseExpression(PrecedenceLevel.Lowest);
if (!ExpectPeek(TokenType.RParen))
{
return(null);
}
if (!ExpectPeek(TokenType.LBrace))
{
return(null);
}
expression.Consequence = ParseBlockStatement();
if (PeekTokenIs(TokenType.Else))
{
NextToken();
if (!ExpectPeek(TokenType.LBrace))
{
return(null);
}
expression.Alternative = ParseBlockStatement();
}
return(expression);
}