public override SchemeObject evaluate( ref SchemeAST currentAST, SchemeEvaluator evaluator )
{
if( currentAST.children.Count < 2 || currentAST.children.Count > 3 )
{
throw new SchemeWrongNumberOfArguments( String.Format( "The If-statement expects 2 or 3 arguments (condition, branch1, branch2). You provided {0}", currentAST.children.Count - 1 ) );
}
_condition = currentAST.children[0];
_trueBranch = currentAST.children[1];
if( currentAST.children.Count == 3 )
{
_falseBranch = currentAST.children[2];
}
if( _condition.currentObject == SchemeTrue.instance )
{
var old_parent = currentAST.parent;
_trueBranch.parent = currentAST.parent;
int postition = currentAST.parent.children.IndexOf( currentAST );
currentAST.parent.children.Remove( currentAST );
currentAST.parent.children.Add( _trueBranch );
currentAST = _trueBranch;
return null;
}
if( _condition.currentObject == SchemeFalse.instance )
{
if( _falseBranch != null )
{
var old_parent = currentAST.parent;
_falseBranch.parent = currentAST.parent;
int postition = currentAST.parent.children.IndexOf( currentAST );
currentAST.parent.children.Remove( currentAST );
currentAST.parent.children.Add( _falseBranch );
currentAST = _falseBranch;
return null;
}
else
{
return SchemeVoid.instance;
}
}
throw new SchemeInvalidArgumentException( String.Format( "Invalid Argument in If-condition: Your condtion has to evalue to either #t or #f, but it evaluated to {0}", _condition.ToString() ) );
}
