private MObject EvalIfExpression(IfExpression node, Environment env)
{
var condition = Eval(node.Condition, env);
if (IsError(condition))
{
return(condition);
}
if (IsTruthy(condition))
{
return(Eval(node.Consequence, env));
}
else if (node.Alternative != null)
{
return(Eval(node.Alternative, env));
}
else
{
return(NIL);
}
}
private Expression ParseIfExpression()
{
var expr = new IfExpression();
expr.Token = curToken;
if (!ExpectPeek(TokenType.LPAREN))
{
return(null);
}
NextToken();
expr.Condition = ParseExpression(Precedence.LOWEST);
if (!ExpectPeek(TokenType.RPAREN))
{
return(null);
}
expr.Consequence = ParseBlockStatement();
if (PeekTokenIs(TokenType.ELSE))
{
NextToken();
if (!ExpectPeek(TokenType.LBRACE))
{
return(null);
}
expr.Alternative = ParseBlockStatement();
}
return(expr);
}