InvAmount expression

//==========================================================================
//
// Function: InvAmount
//
//==========================================================================

class FxGlobalFunctionCall_InvAmount : public FxGlobalFunctionCall
{
public:
    GLOBALFUNCTION_DEFINE(InvAmount);

    FxExpression *Resolve(FCompileContext& ctx)
    {
        CHECKRESOLVED();

        if (!ResolveArgs(ctx, 1, 1, false))
            return NULL;

        switch ((*ArgList)[0]->ValueType.Type)
        {
        case VAL_Class: case VAL_Name:break;
        default:
            ScriptPosition.Message(MSG_ERROR, "actor class expected for parameter");
            delete this;
            return NULL;
        }

        ValueType = VAL_Float;
        return this;
    }

    ExpVal EvalExpression(AActor *self)
    {
        ExpVal ret;
        ret.Type = VAL_Int;
        ExpVal v = (*ArgList)[0]->EvalExpression(self);
        const PClass  * invclass;
        {
            invclass = v.GetClass();
            if (!invclass)
            {
                invclass = PClass::FindClass(v.GetName());
                if (!invclass){ ret.Int = -1; return ret; }
            }
        }
        AInventory *item = self->FindInventory(invclass);
        int pick_pointer = AAPTR_DEFAULT;

        self = COPY_AAPTR(self, pick_pointer);
        ret.Int = (item == NULL) ? -1 : item->Amount;
        return ret;
    }
};

GLOBALFUNCTION_ADDER(InvAmount);