picoc/expression.c

#include "picoc.h"


/* whether evaluation is left to right for a given precedence level */
#define IS_LEFT_TO_RIGHT(p) ((p) != 2 && (p) != 3 && (p) != 14)
#ifndef NO_FP
#define IS_INTEGER_COERCIBLE(v) ((v)->Typ->Base == TypeInt || (v)->Typ->Base == TypeFP || (v)->Typ->Base == TypeChar)
#define COERCE_INTEGER(v) (((v)->Typ->Base == TypeFP) ? (int)(v)->Val->FP : (v)->Val->Integer)
#else
#define IS_INTEGER_COERCIBLE(v) ((v)->Typ->Base == TypeInt || (v)->Typ->Base == TypeChar)
#define COERCE_INTEGER(v) ((v)->Val->Integer)
#endif

#define BRACKET_PRECEDENCE 20


#if 1
/* local prototypes */
void ExpressionParseFunctionCall(struct ParseState *Parser, struct Value **Result, const char *FuncName);

/* parse a single value */
int ExpressionParseValue(struct ParseState *Parser, struct Value **Result)
{
    struct ParseState PreState = *Parser;
    struct Value *LexValue;
    int IntValue;
    enum LexToken Token = LexGetToken(Parser, &LexValue, TRUE);
    struct Value *LocalLValue = NULL;
    struct ValueType *VType;
    char *Identifier;
    int Success = TRUE;
    
    switch (Token)
    {
        case TokenIntegerConstant: case TokenCharacterConstant: case TokenFPConstant: case TokenStringConstant:
            *Result = VariableAllocValueAndCopy(Parser, LexValue, FALSE);
            break;
        
        case TokenMinus:  case TokenUnaryExor: case TokenUnaryNot:
            IntValue = ExpressionParseInt(Parser);
            if (Parser->Mode == RunModeRun)
            {
                *Result = VariableAllocValueFromType(Parser, &IntType, FALSE, NULL);
                switch(Token)
                {
                    case TokenMinus: (*Result)->Val->Integer = -IntValue; break;
                    case TokenUnaryExor: (*Result)->Val->Integer = ~IntValue; break;
                    case TokenUnaryNot: (*Result)->Val->Integer = !IntValue; break;
                    default: break;
                }
            }
            break;

        case TokenOpenBracket:
            if (!ExpressionParse(Parser, Result))
                ProgramFail(Parser, "invalid expression");
            
            if (LexGetToken(Parser, NULL, TRUE) != TokenCloseBracket)
                ProgramFail(Parser, "')' expected");
            break;
                
        case TokenAsterisk:
            if (!ExpressionParse(Parser, Result))
                ProgramFail(Parser, "invalid expression");
            
            if ((*Result)->Typ->Base != TypePointer)
                ProgramFail(Parser, "can't dereference this non-pointer");
            
            LocalLValue = (*Result)->Val->Pointer.Segment;
            VariableStackPop(Parser, *Result);
            *Result = VariableAllocValueShared(Parser, LocalLValue);
            break;

        case TokenAmpersand:
            if (!ExpressionParseValue(Parser, Result) || !(*Result)->IsLValue)
                ProgramFail(Parser, "can't get the address of this");
            
            VType = (*Result)->Typ;
            LocalLValue = (*Result)->LValueFrom;
            VariableStackPop(Parser, *Result);
            *Result = VariableAllocValueFromType(Parser, TypeGetMatching(Parser, VType, TypePointer, 0, StrEmpty), FALSE, NULL);
            (*Result)->Val->Pointer.Segment = LocalLValue;
            (*Result)->Val->Pointer.Offset = (void *)(*Result)->Val - (void *)(*Result)->LValueFrom;
            break;
            
        case TokenIdentifier:
            if (LexGetToken(Parser, NULL, FALSE) == TokenOpenBracket)
                ExpressionParseFunctionCall(Parser, Result, LexValue->Val->Identifier);
            else
            {
                if (Parser->Mode == RunModeRun)
                {
                    VariableGet(Parser, LexValue->Val->Identifier, &LocalLValue);
                    if (LocalLValue->Typ->Base == TypeMacro)
                    {
                        struct ParseState MacroParser = LocalLValue->Val->Parser;
                        
                        if (!ExpressionParse(&MacroParser, Result) || LexGetToken(&MacroParser, NULL, FALSE) != TokenEndOfFunction)
                            ProgramFail(&MacroParser, "expression expected");
                    }
                    else if (LocalLValue->Typ == TypeVoid)
                        ProgramFail(Parser, "a void value isn't much use here");
                    else
                    { /* it's a value variable */
                        *Result = VariableAllocValueShared(Parser, LocalLValue);
                    }
                }
                
                /* see if there's a postfix operator */
                Token = LexGetToken(Parser, &LexValue, FALSE);
                if (Token == TokenIncrement || Token == TokenDecrement)
                { /* it's a postincrement or postdecrement */
                    LexGetToken(Parser, &LexValue, TRUE);
                    if (Parser->Mode == RunModeRun)
                    {
                        if (!(*Result)->IsLValue || (*Result)->Typ->Base != TypeInt) 
                            ProgramFail(Parser, "can't %s this", (Token == TokenIncrement) ? "increment" : "decrement");
                            
                        if (Token == TokenIncrement)
                            (*Result)->Val->Integer++;
                        else
                            (*Result)->Val->Integer--;
                    }
                }
                else if (Token == TokenLeftSquareBracket)
                { /* array access */
                    LexGetToken(Parser, &LexValue, TRUE);
                    IntValue = ExpressionParseInt(Parser);
                    if (LexGetToken(Parser, &LexValue, TRUE) != TokenRightSquareBracket)
                        ProgramFail(Parser, "expected ']'");
                    
                    if (Parser->Mode == RunModeRun)
                    { /* look up the array element */
                        if ((*Result)->Typ->Base != TypeArray)
                            ProgramFail(Parser, "not an array");
                        
                        if (IntValue < 0 || IntValue >= (*Result)->Val->Array.Size)
                            ProgramFail(Parser, "illegal array index");
                        
                        VariableStackPop(Parser, *Result);
                        *Result = VariableAllocValueFromExistingData(Parser, (*Result)->Typ->FromType, (union AnyValue *)((*Result)->Val->Array.Data + TypeSize((*Result)->Typ->FromType, 0) * IntValue), (*Result)->IsLValue, (*Result)->LValueFrom);
                    }
                }
            }
            break;

        case TokenNew:
            TypeParse(Parser, &VType, &Identifier);
            if (Identifier != StrEmpty)
                ProgramFail(Parser, "identifier not expected here");
            
            if (Parser->Mode == RunModeRun)
            { /* create an object of this type on the heap and a pointer to it on the stack */
                LocalLValue = VariableAllocValueFromType(Parser, VType, TRUE, NULL);
                *Result = VariableAllocValueFromType(Parser, TypeGetMatching(Parser, VType, TypePointer, 0, StrEmpty), FALSE, NULL);
                (*Result)->Val->Pointer.Segment = LocalLValue;
                (*Result)->Val->Pointer.Offset = 0;
            }
            break;
            
        default:
            *Parser = PreState;
            Success = FALSE;
            break;
    }
    
    return Success;
}

#ifndef NO_FP
struct Value *ParsePushFP(struct ParseState *Parser, double NewFP)
{
    struct Value *Val = VariableAllocValueFromType(Parser, &FPType, FALSE, NULL);
    Val->Val->FP = NewFP;
    return Val;
}
#endif

struct Value *ParsePushInt(struct ParseState *Parser, int NewInt)
{
    struct Value *Val = VariableAllocValueFromType(Parser, &IntType, FALSE, NULL);
    Val->Val->Integer = NewInt;
    return Val;
}

/* parse an expression. operator precedence is not supported */
int ExpressionParse(struct ParseState *Parser, struct Value **Result)
{
    struct Value *CurrentValue;
    struct Value *TotalValue;
    
    if (!ExpressionParseValue(Parser, &TotalValue))
        return FALSE;
    
    while (TRUE)
    {
        enum LexToken Token = LexGetToken(Parser, NULL, FALSE);
        switch (Token)
        {
            case TokenPlus: case TokenMinus: case TokenAsterisk: case TokenSlash:
            case TokenEqual: case TokenLessThan: case TokenGreaterThan:
            case TokenLessEqual: case TokenGreaterEqual: case TokenLogicalAnd:
            case TokenLogicalOr: case TokenAmpersand: case TokenArithmeticOr: 
            case TokenArithmeticExor: 
                LexGetToken(Parser, NULL, TRUE);
                break;
            
            case TokenDot:
            {
                struct Value *Ident;
                
                LexGetToken(Parser, NULL, TRUE);
                if (LexGetToken(Parser, &Ident, TRUE) != TokenIdentifier)
                    ProgramFail(Parser, "need an structure or union member after '.'");

                if (Parser->Mode == RunModeRun)
                {                
                    void *TotalValueData = (void *)TotalValue->Val;
                    struct Value *TotalLValueFrom = TotalValue->LValueFrom;

                    if (TotalValue->Typ->Base != TypeStruct && TotalValue->Typ->Base != TypeUnion)
                        ProgramFail(Parser, "can't use '.' on something that's not a struct or union");
                        
                    if (!TableGet(TotalValue->Typ->Members, Ident->Val->Identifier, &CurrentValue))
                        ProgramFail(Parser, "structure doesn't have a member called '%s'", Ident->Val->Identifier);
                    
                    VariableStackPop(Parser, TotalValue);
                    TotalValue = VariableAllocValueFromExistingData(Parser, CurrentValue->Typ, TotalValueData + CurrentValue->Val->Integer, TRUE, TotalLValueFrom);
                }
                continue;
            }
            case TokenArrow:
            {
                struct Value *Ident;
                
                LexGetToken(Parser, NULL, TRUE);
                if (LexGetToken(Parser, &Ident, TRUE) != TokenIdentifier)
                    ProgramFail(Parser, "need an structure or union member after '->'");

                if (Parser->Mode == RunModeRun)
                {                
                    void *TotalValueData;
                    struct Value *DerefValue;

                    if (TotalValue->Typ->Base != TypePointer)
                        ProgramFail(Parser, "can't dereference this non-pointer");
                    
                    DerefValue = TotalValue->Val->Pointer.Segment;
                    TotalValueData = (void *)DerefValue->Val;

                    if (DerefValue->Typ->Base != TypeStruct && DerefValue->Typ->Base != TypeUnion)
                        ProgramFail(Parser, "can't use '->' on something that's not a struct or union");
                        
                    if (!TableGet(DerefValue->Typ->Members, Ident->Val->Identifier, &CurrentValue))
                        ProgramFail(Parser, "structure doesn't have a member called '%s'", Ident->Val->Identifier);
                    
                    VariableStackPop(Parser, TotalValue);
                    TotalValue = VariableAllocValueFromExistingData(Parser, CurrentValue->Typ, TotalValueData + CurrentValue->Val->Integer, TRUE, DerefValue);
                }
                continue;
            }
            case TokenAssign: 
                LexGetToken(Parser, NULL, TRUE);
            
                if (!ExpressionParse(Parser, &CurrentValue))
                    ProgramFail(Parser, "expression expected");
                    
                if (Parser->Mode == RunModeRun)
                { /* do the assignment */
                    if (!TotalValue->IsLValue)
                        ProgramFail(Parser, "can't assign to this");

                    if (CurrentValue->Typ != TotalValue->Typ)
                        ProgramFail(Parser, "can't assign incompatible types");

                    if (TotalValue->Typ->Base != TypeArray)
                        memcpy((void *)TotalValue->Val, (void *)CurrentValue->Val, TotalValue->Typ->Sizeof);
                    else
                    { /* array assignment */
                        if (TotalValue->Val->Array.Size != CurrentValue->Val->Array.Size)
                            ProgramFail(Parser, "incompatible array sizes in assignment");
                        
                        //memcpy(TotalValue->Val->Array.Data, CurrentValue->Val->Array.Data, CurrentValue->Typ->Sizeof * CurrentValue->Val->Array.Size);
                    }
                    VariableStackPop(Parser, CurrentValue);
                    *Result = TotalValue;
                }
                return TRUE;
                
            case TokenAddAssign: case TokenSubtractAssign:
                LexGetToken(Parser, NULL, TRUE);
            
                if (!ExpressionParse(Parser, &CurrentValue))
                    ProgramFail(Parser, "expression expected");
                
                if (Parser->Mode == RunModeRun)
                { /* do the assignment */
                    if (!TotalValue->IsLValue)
                        ProgramFail(Parser, "can't assign");

                    if (CurrentValue->Typ->Base == TypeInt && TotalValue->Typ->Base == TypeInt)
                    {
                        switch (Token)
                        {
                            case TokenAddAssign: TotalValue->Val->Integer += CurrentValue->Val->Integer; break;
                            case TokenSubtractAssign: TotalValue->Val->Integer -= CurrentValue->Val->Integer; break;
                            default: break;
                        }
                        VariableStackPop(Parser, CurrentValue);
                    }
#ifndef NO_FP
                    else if (CurrentValue->Typ->Base == TypeFP && TotalValue->Typ->Base == TypeFP)
                    {
                        switch (Token)
                        {
                            case TokenAddAssign: TotalValue->Val->FP += CurrentValue->Val->FP; break;
                            case TokenSubtractAssign: TotalValue->Val->FP -= CurrentValue->Val->FP; break;
                            default: break;
                        }
                        VariableStackPop(Parser, CurrentValue);
                    }
#endif
                    else
                        ProgramFail(Parser, "can't operate and assign these types");
                }
                // fallthrough
            
            default:
                if (Parser->Mode == RunModeRun)
                    *Result = TotalValue;
                return TRUE;
        }
        
        if (!ExpressionParseValue(Parser, &CurrentValue))
            return FALSE;

        if (Parser->Mode == RunModeRun)
        {
#ifndef NO_FP
            if (CurrentValue->Typ->Base == TypeFP || TotalValue->Typ->Base == TypeFP)
            { /* floating point expression */
                double FPTotal, FPCurrent, FPResult;

                if (CurrentValue->Typ->Base != TypeFP || TotalValue->Typ->Base != TypeFP)
                { /* convert both to floating point */
                    if (CurrentValue->Typ->Base == TypeInt)
                        FPCurrent = (double)CurrentValue->Val->Integer;
                    else if (CurrentValue->Typ->Base == TypeFP)
                        FPCurrent = CurrentValue->Val->FP;
                    else
                        ProgramFail(Parser, "bad type for operator");
                        
                    if (TotalValue->Typ->Base == TypeInt)
                        FPTotal = (double)TotalValue->Val->Integer;
                    else if (TotalValue->Typ->Base == TypeFP)
                        FPTotal = TotalValue->Val->FP;
                    else
                        ProgramFail(Parser, "bad type for operator");
                }

                VariableStackPop(Parser, CurrentValue);
                VariableStackPop(Parser, TotalValue);
                
                switch (Token)
                {
                    case TokenPlus:         FPResult = FPTotal + FPCurrent; break;
                    case TokenMinus:        FPResult = FPTotal - FPCurrent; break;
                    case TokenAsterisk:     FPResult = FPTotal * FPCurrent; break;
                    case TokenSlash:        FPResult = FPTotal / FPCurrent; break;
                    case TokenEqual:        FPResult = FPTotal == FPCurrent; break;
                    case TokenLessThan:     FPResult = FPTotal < FPCurrent; break;
                    case TokenGreaterThan:  FPResult = FPTotal > FPCurrent; break;
                    case TokenLessEqual:    FPResult = FPTotal <= FPCurrent; break;
                    case TokenGreaterEqual: FPResult = FPTotal >= FPCurrent; break;
                    case TokenLogicalAnd: case TokenLogicalOr: case TokenAmpersand: case TokenArithmeticOr: case TokenArithmeticExor: ProgramFail(Parser, "bad type for operator"); break;
                    default: break;
                }
                TotalValue = ParsePushFP(Parser, FPResult);
            }
            else
#endif
            { /* integer expression */
                int IntX, IntY, IntResult;
                
                if (CurrentValue->Typ->Base != TypeInt || TotalValue->Typ->Base != TypeInt)
                    ProgramFail(Parser, "bad operand types");
            
                IntX = TotalValue->Val->Integer;
                IntY = CurrentValue->Val->Integer;
                VariableStackPop(Parser, CurrentValue);
                VariableStackPop(Parser, TotalValue);
                
                /* integer arithmetic */
                switch (Token)
                {
                    case TokenPlus:             IntResult = IntX + IntY; break;
                    case TokenMinus:            IntResult = IntX - IntY; break;
                    case TokenAsterisk:         IntResult = IntX * IntY; break;
                    case TokenSlash:            IntResult = IntX / IntY; break;
                    case TokenEqual:            IntResult = IntX == IntY; break;
                    case TokenLessThan:         IntResult = IntX < IntY; break;
                    case TokenGreaterThan:      IntResult = IntX > IntY; break;
                    case TokenLessEqual:        IntResult = IntX <= IntY; break;
                    case TokenGreaterEqual:     IntResult = IntX >= IntY; break;
                    case TokenLogicalAnd:       IntResult = IntX && IntY; break;
                    case TokenLogicalOr:        IntResult = IntX || IntY; break;
                    case TokenAmpersand:        IntResult = IntX & IntY; break;
                    case TokenArithmeticOr:     IntResult = IntX | IntY; break;
                    case TokenArithmeticExor:   IntResult = IntX ^ IntY; break;
                    default:                    IntResult = 0; break;
                }
                TotalValue = ParsePushInt(Parser, IntResult);
            }
            
            *Result = TotalValue;
        }
    }
    
    return TRUE;
}

/* do a function call */
void ExpressionParseFunctionCall(struct ParseState *Parser, struct Value **Result, const char *FuncName)
{
    struct Value *FuncValue;
    struct Value *Param;
    struct Value **ParamArray = NULL;
    int ArgCount;
    enum LexToken Token = LexGetToken(Parser, NULL, TRUE);    /* open bracket */
    
    if (Parser->Mode == RunModeRun) 
    { /* get the function definition */
        VariableGet(Parser, FuncName, &FuncValue);
        if (FuncValue->Typ->Base != TypeFunction)
            ProgramFail(Parser, "not a function - can't call");
    
        *Result = VariableAllocValueFromType(Parser, FuncValue->Val->FuncDef.ReturnType, FALSE, NULL);
        HeapPushStackFrame();
        ParamArray = HeapAllocStack(sizeof(struct Value *) * FuncValue->Val->FuncDef.NumParams);
        if (ParamArray == NULL)
            ProgramFail(Parser, "out of memory");
    }
        
    /* parse arguments */
    ArgCount = 0;
    do {
        if (ExpressionParse(Parser, &Param))
        {
            if (Parser->Mode == RunModeRun)
            { 
                if (ArgCount >= FuncValue->Val->FuncDef.NumParams)
                {
                    if (!FuncValue->Val->FuncDef.VarArgs)
                        ProgramFail(Parser, "too many arguments to %s()", FuncName);
                }
                else
                {
                    if (FuncValue->Val->FuncDef.ParamType[ArgCount] != Param->Typ)
                        ProgramFail(Parser, "parameter %d to %s() is the wrong type", ArgCount+1, FuncName);
                }
                
                if (ArgCount < FuncValue->Val->FuncDef.NumParams)
                    ParamArray[ArgCount] = Param;
            }
            
            ArgCount++;
            Token = LexGetToken(Parser, NULL, TRUE);
            if (Token != TokenComma && Token != TokenCloseBracket)
                ProgramFail(Parser, "comma expected");
        }
        else
        { /* end of argument list? */
            Token = LexGetToken(Parser, NULL, TRUE);
            if (!TokenCloseBracket)
                ProgramFail(Parser, "bad argument");
        }
    } while (Token != TokenCloseBracket);
    
    if (Parser->Mode == RunModeRun) 
    { /* run the function */
        if (ArgCount < FuncValue->Val->FuncDef.NumParams)
            ProgramFail(Parser, "not enough arguments to '%s'", FuncName);
        
        if (FuncValue->Val->FuncDef.Intrinsic == NULL)
        { /* run a user-defined function */
            struct ParseState FuncParser = FuncValue->Val->FuncDef.Body;
            int Count;
            
            VariableStackFrameAdd(Parser, FuncValue->Val->FuncDef.Intrinsic ? FuncValue->Val->FuncDef.NumParams : 0);
            TopStackFrame->NumParams = ArgCount;
            TopStackFrame->ReturnValue = *Result;
            for (Count = 0; Count < FuncValue->Val->FuncDef.NumParams; Count++)
                VariableDefine(Parser, FuncValue->Val->FuncDef.ParamName[Count], ParamArray[Count]);
                
            if (!ParseStatement(&FuncParser))
                ProgramFail(&FuncParser, "function body expected");
        
            if (FuncValue->Val->FuncDef.ReturnType != (*Result)->Typ)
                ProgramFail(&FuncParser, "bad type of return value");

            VariableStackFramePop(Parser);
        }
        else
            FuncValue->Val->FuncDef.Intrinsic(Parser, *Result, ParamArray, ArgCount);

        HeapPopStackFrame();
    }
}
#else

/* local prototypes */
enum OperatorOrder
{
    OrderNone,
    OrderPrefix,
    OrderInfix,
    OrderPostfix
};

/* a stack of expressions we use in evaluation */
struct ExpressionStack
{
    struct ExpressionStack *Next;   /* the next lower item on the stack */
    struct Value *Val;              /* the value for this stack node */
    enum OperatorOrder Order;       /* the evaluation order of this operator */
    enum LexToken Op;               /* the operator */
    int Precedence;                 /* the operator precedence of this node */
};

/* operator precedence definitions */
struct OpPrecedence
{
    unsigned char PrefixPrecedence:4;
    unsigned char PostfixPrecedence:4;
    unsigned char InfixPrecedence:4;
};

static struct OpPrecedence OperatorPrecedence[] =
{
    /* TokenNone, */ { 0, 0, 0 },
    /* TokenComma, */ { 0, 0, 1 },
    /* TokenAssign, */ { 0, 0, 2 }, /* TokenAddAssign, */ { 0, 0, 2 }, /* TokenSubtractAssign, */ { 0, 0, 2 }, 
    /* TokenMultiplyAssign, */ { 0, 0, 2 }, /* TokenDivideAssign, */ { 0, 0, 2 }, /* TokenModulusAssign, */ { 0, 0, 2 },
    /* TokenShiftLeftAssign, */ { 0, 0, 2 }, /* TokenShiftRightAssign, */ { 0, 0, 2 }, /* TokenArithmeticAndAssign, */ { 0, 0, 2 }, 
    /* TokenArithmeticOrAssign, */ { 0, 0, 2 }, /* TokenArithmeticExorAssign, */ { 0, 0, 2 },
    /* TokenQuestionMark, */ { 0, 0, 3 }, /* TokenColon, */ { 0, 0, 3 },
    /* TokenLogicalOr, */ { 0, 0, 4 },
    /* TokenLogicalAnd, */ { 0, 0, 5 },
    /* TokenArithmeticOr, */ { 0, 0, 6 },
    /* TokenArithmeticExor, */ { 0, 0, 7 },
    /* TokenAmpersand, */ { 14, 0, 8 },
    /* TokenEqual, */  { 0, 0, 9 }, /* TokenNotEqual, */ { 0, 0, 9 },
    /* TokenLessThan, */ { 0, 0, 10 }, /* TokenGreaterThan, */ { 0, 0, 10 }, /* TokenLessEqual, */ { 0, 0, 10 }, /* TokenGreaterEqual, */ { 0, 0, 10 },
    /* TokenShiftLeft, */ { 0, 0, 11 }, /* TokenShiftRight, */ { 0, 0, 11 },
    /* TokenPlus, */ { 14, 0, 12 }, /* TokenMinus, */ { 14, 0, 12 },
    /* TokenAsterisk, */ { 14, 0, 13 }, /* TokenSlash, */ { 0, 0, 13 }, /* TokenModulus, */ { 0, 0, 13 },
    /* TokenIncrement, */ { 14, 15, 0 }, /* TokenDecrement, */ { 14, 15, 0 }, /* TokenUnaryNot, */ { 14, 0, 0 }, /* TokenUnaryExor, */ { 14, 0, 0 }, /* TokenSizeof, */ { 14, 0, 0 },
    /* TokenLeftSquareBracket, */ { 15, 0, 0 }, /* TokenRightSquareBracket, */ { 0, 15, 0 }, /* TokenDot, */ { 0, 0, 15 }, /* TokenArrow, */ { 0, 0, 15 },
    /* TokenOpenBracket, */ { 15, 0, 0 }, /* TokenCloseBracket, */ { 0, 15, 0 }
};

void ExpressionParseFunctionCall(struct ParseState *Parser, struct ExpressionStack **StackTop, const char *FuncName);


/* push a node on to the expression stack */
void ExpressionStackPushValueNode(struct ParseState *Parser, struct ExpressionStack **StackTop, struct Value *ValueLoc)
{
    struct ExpressionStack *StackNode = VariableAlloc(Parser, sizeof(struct ExpressionStack), FALSE);
    StackNode->Next = *StackTop;
    StackNode->Val = ValueLoc;
    *StackTop = StackNode;
}

/* push a blank value on to the expression stack by type */
void ExpressionStackPushValueByType(struct ParseState *Parser, struct ExpressionStack **StackTop, struct ValueType *PushType)
{
    struct Value *ValueLoc = VariableAllocValueFromType(Parser, PushType, FALSE, NULL);
    ExpressionStackPushValueNode(Parser, StackTop, ValueLoc);
}

/* push a value on to the expression stack */
void ExpressionStackPushValue(struct ParseState *Parser, struct ExpressionStack **StackTop, struct Value *PushValue)
{
    struct Value *ValueLoc = VariableAllocValueAndCopy(Parser, PushValue, FALSE);
    ExpressionStackPushValueNode(Parser, StackTop, ValueLoc);
}

void ExpressionPushInt(struct ParseState *Parser, struct ExpressionStack **StackTop, int IntValue)
{
    struct Value *ValueLoc = VariableAllocValueFromType(Parser, &IntType, FALSE, NULL);
    ValueLoc->Val->Integer = IntValue;
    ExpressionStackPushValueNode(Parser, StackTop, ValueLoc);
}

void ExpressionPushFP(struct ParseState *Parser, struct ExpressionStack **StackTop, double FPValue)
{
    struct Value *ValueLoc = VariableAllocValueFromType(Parser, &FPType, FALSE, NULL);
    ValueLoc->Val->FP = FPValue;
    ExpressionStackPushValueNode(Parser, StackTop, ValueLoc);
}

/* evaluate a prefix operator */
void ExpressionPrefixOperator(struct ParseState *Parser, struct ExpressionStack **StackTop, enum LexToken Op, struct Value *TopValue)
{
    struct Value *TempLValue;
    struct Value *Result;

    switch (Op)
    {
        case TokenAmpersand:
            if (!TopValue->IsLValue)
                ProgramFail(Parser, "can't get the address of this");

            TempLValue = TopValue->LValueFrom;
            Result = VariableAllocValueFromType(Parser, TypeGetMatching(Parser, TopValue->Typ, TypePointer, 0, StrEmpty), FALSE, NULL);
            Result->Val->Pointer.Segment = TempLValue;
            Result->Val->Pointer.Offset = (void *)Result->Val - (void *)Result->LValueFrom;
            ExpressionStackPushValueNode(Parser, StackTop, Result);
            break;

        case TokenAsterisk:
            if (TopValue->Typ->Base != TypePointer)
                ProgramFail(Parser, "can't dereference this non-pointer");
            
            Result = VariableAllocValueShared(Parser, TopValue->Val->Pointer.Segment);
            ExpressionStackPushValueNode(Parser, StackTop, Result);
            break;
        
        case TokenSizeof:
            // XXX
            break;
        
        case TokenLeftSquareBracket:
            // XXX
            break;
        
        case TokenOpenBracket:
            // XXX
            break;

        default:
            /* an arithmetic operator */
            if (IS_INTEGER_COERCIBLE(TopValue))
            {
                /* integer prefix arithmetic */
                int ResultInt;
                int TopInt = COERCE_INTEGER(TopValue);
                switch (Op)
                {
                    case TokenPlus:         ResultInt = TopInt; break;
                    case TokenMinus:        ResultInt = -TopInt; break;
                    case TokenIncrement:    TopValue->Val->Integer++; ResultInt = COERCE_INTEGER(TopValue); break;  // XXX - what about non-lvalues?
                    case TokenDecrement:    TopValue->Val->Integer--; ResultInt = COERCE_INTEGER(TopValue); break;  // XXX - what about non-lvalues?
                    case TokenUnaryNot:     ResultInt = !TopInt; break;
                    case TokenUnaryExor:    ResultInt = ~TopInt; break;
                    default:                ProgramFail(Parser, "invalid operation"); break;
                }

                ExpressionPushInt(Parser, StackTop, ResultInt);
            }
#ifndef NO_FP
            else if (TopValue->Typ == &FPType)
            {
                /* floating point prefix arithmetic */
                double ResultFP;
                switch (Op)
                {
                    case TokenPlus:         ResultFP = TopValue->Val->FP; break;
                    case TokenMinus:        ResultFP = -TopValue->Val->FP; break;
                    default:                ProgramFail(Parser, "invalid operation"); break;
                }
            }
#endif
#if 0
XXX - finish this
            else
            {
                /* pointer prefix arithmetic */
                int TopInt = COERCE_INTEGER(TopValue);
            }
#endif
            break;
    }
}

/* evaluate a postfix operator */
void ExpressionPostfixOperator(struct ParseState *Parser, struct ExpressionStack **StackTop, enum LexToken Op, struct Value *TopValue)
{
    if (IS_INTEGER_COERCIBLE(TopValue))
    {
        int ResultInt;
        int TopInt = COERCE_INTEGER(TopValue);
        switch (Op)
        {
            case TokenIncrement:            ResultInt = TopInt; TopValue->Val->Integer++; break;  // XXX - what about non-lvalues?
            case TokenDecrement:            ResultInt = TopInt; TopValue->Val->Integer--; break;  // XXX - what about non-lvalues?
            case TokenRightSquareBracket:   break;  // XXX
            case TokenCloseBracket:         break;  // XXX
            default:                        ProgramFail(Parser, "invalid operation"); break;
        }
    
        ExpressionPushInt(Parser, StackTop, ResultInt);
    }
}

/* evaluate an infix operator */
void ExpressionInfixOperator(struct ParseState *Parser, struct ExpressionStack **StackTop, enum LexToken Op, struct Value *BottomValue, struct Value *TopValue)
{
    int ResultIsInt = FALSE;
    int ResultInt;

    switch (Op)
    {
        case TokenComma:
        case TokenAssign:
        case TokenDot:
        case TokenArrow:
        default:
            if (IS_INTEGER_COERCIBLE(TopValue) && IS_INTEGER_COERCIBLE(BottomValue))
            {
                int TopInt = COERCE_INTEGER(TopValue);
                int BottomInt = COERCE_INTEGER(BottomValue);
                switch (Op)
                {
                    case TokenAddAssign:            break; // XXX
                    case TokenSubtractAssign:       break; // XXX
                    case TokenMultiplyAssign:       break; // XXX
                    case TokenDivideAssign:         break; // XXX
                    case TokenModulusAssign:        break; // XXX
                    case TokenShiftLeftAssign:      break; // XXX
                    case TokenShiftRightAssign:     break; // XXX
                    case TokenArithmeticAndAssign:  break; // XXX
                    case TokenArithmeticOrAssign:   break; // XXX
                    case TokenArithmeticExorAssign: break; // XXX
                    case TokenQuestionMark:         break; // XXX
                    case TokenColon:                break; // XXX
                    case TokenLogicalOr:            ResultInt = BottomInt || TopInt; break;
                    case TokenLogicalAnd:           ResultInt = BottomInt && TopInt; break;
                    case TokenArithmeticOr:         ResultInt = BottomInt | TopInt; break;
                    case TokenArithmeticExor:       ResultInt = BottomInt ^ TopInt; break;
                    case TokenAmpersand:            ResultInt = BottomInt & TopInt; break;
                    case TokenEqual:                ResultInt = BottomInt == TopInt; break;
                    case TokenNotEqual:             ResultInt = BottomInt != TopInt; break;
                    case TokenLessThan:             ResultInt = BottomInt < TopInt; break;
                    case TokenGreaterThan:          ResultInt = BottomInt > TopInt; break;
                    case TokenLessEqual:            ResultInt = BottomInt <= TopInt; break;
                    case TokenGreaterEqual:         ResultInt = BottomInt >= TopInt; break;
                    case TokenShiftLeft:            ResultInt = BottomInt << TopInt; break;
                    case TokenShiftRight:           ResultInt = BottomInt << TopInt; break;
                    case TokenPlus:                 ResultInt = BottomInt + TopInt; break;
                    case TokenMinus:                ResultInt = BottomInt - TopInt; break;
                    case TokenAsterisk:             ResultInt = BottomInt * TopInt; break;
                    case TokenSlash:                ResultInt = BottomInt / TopInt; break;
                    case TokenModulus:              ResultInt = BottomInt % TopInt; break;
                    default:                        ProgramFail(Parser, "invalid operation"); break;
                }
                
                ExpressionPushInt(Parser, StackTop, ResultInt);
            }
#ifndef NO_FP
            else if ( (TopValue->Typ == &FPType && BottomValue->Typ == &FPType) ||
                      (TopValue->Typ == &FPType && IS_INTEGER_COERCIBLE(BottomValue)) ||
                      (IS_INTEGER_COERCIBLE(TopValue) && BottomValue->Typ == &FPType) )
            {
                /* floating point infix arithmetic */
                double ResultFP;
                double TopFP = (TopValue->Typ == &FPType) ? TopValue->Val->FP : (double)COERCE_INTEGER(TopValue);
                double BottomFP = (BottomValue->Typ == &FPType) ? BottomValue->Val->FP : (double)COERCE_INTEGER(BottomValue);

                switch (Op)
                {
                    case TokenAddAssign:            break; // XXX
                    case TokenSubtractAssign:       break; // XXX
                    case TokenMultiplyAssign:       break; // XXX
                    case TokenDivideAssign:         break; // XXX
                    case TokenModulusAssign:        break; // XXX
                    case TokenEqual:                ResultInt = BottomFP == TopFP; ResultIsInt = TRUE; break;
                    case TokenNotEqual:             ResultInt = BottomFP != TopFP; ResultIsInt = TRUE; break;
                    case TokenLessThan:             ResultInt = BottomFP < TopFP; ResultIsInt = TRUE; break;
                    case TokenGreaterThan:          ResultInt = BottomFP > TopFP; ResultIsInt = TRUE; break;
                    case TokenLessEqual:            ResultInt = BottomFP <= TopFP; ResultIsInt = TRUE; break;
                    case TokenGreaterEqual:         ResultInt = BottomFP >= TopFP; ResultIsInt = TRUE; break;
                    case TokenPlus:                 ResultFP = BottomFP + TopFP; break;
                    case TokenMinus:                ResultFP = BottomFP - TopFP; break;
                    case TokenAsterisk:             ResultFP = BottomFP * TopFP; break;
                    case TokenSlash:                ResultFP = BottomFP / TopFP; break;
                    default:                        ProgramFail(Parser, "invalid operation"); break;
                }

                if (ResultIsInt)
                    ExpressionPushInt(Parser, StackTop, ResultInt);
                else
                    ExpressionPushFP(Parser, StackTop, ResultFP);
            }
#endif
#if 0
XXX - finish this
            else if ( (TopValue->Typ->Base == TypePointer && IS_INTEGER_COERCIBLE(BottomValue)) ||
                      (IS_INTEGER_COERCIBLE(TopValue) && BottomValue->Typ->Base == TypePointer) )
            {
                /* pointer infix arithmetic */
                
                switch (TopOperatorNode->Op)
                {
                    case TokenEqual:                ResultInt = BottomInt == TopInt; ResultIsInt = TRUE; break;
                    case TokenNotEqual:             ResultInt = BottomInt != TopInt; ResultIsInt = TRUE; break;
                    case TokenLessThan:             ResultInt = BottomInt < TopInt; ResultIsInt = TRUE; break;
                    case TokenGreaterThan:          ResultInt = BottomInt > TopInt; ResultIsInt = TRUE; break;
                    case TokenLessEqual:            ResultInt = BottomInt <= TopInt; ResultIsInt = TRUE; break;
                    case TokenGreaterEqual:         ResultInt = BottomInt >= TopInt; ResultIsInt = TRUE; break;
                    case TokenPlus:                 Result = BottomInt + TopInt; break;
                    case TokenMinus:                Result = BottomInt - TopInt; break;
                    default:                        ProgramFail(Parser, "invalid operation"); break;
                }
                
                if (ResultIsInt)
                    ExpressionPushInt(Parser, StackTop, ResultInt);
                else
                    ExpressionPushPointer(Parser, StackTop, ResultInt);
            }
#endif
            else
                ProgramFail(Parser, "invalid operation"); break;
            break;
    }
}

/* take the contents of the expression stack and compute the top until there's nothing greater than the given precedence */
void ExpressionStackCollapse(struct ParseState *Parser, struct ExpressionStack **StackTop, int Precedence)
{
    int FoundPrecedence = Precedence;
    struct Value *TopValue;
    struct Value *BottomValue;
    struct ExpressionStack *TopStackNode = *StackTop;
    struct ExpressionStack *TopOperatorNode;
    
    while (TopStackNode != NULL && TopStackNode->Next != NULL && FoundPrecedence >= Precedence)
    {
        /* find the top operator on the stack */
        if (TopStackNode->Val != NULL)
            TopOperatorNode = TopStackNode->Next;
        else
            TopOperatorNode = TopStackNode;
        
        /* does it have a high enough precedence? */
        if (FoundPrecedence >= Precedence && TopOperatorNode != NULL)
        {
            /* execute this operator */
            switch (TopOperatorNode->Order)
            {
                case OrderPrefix:
                    /* prefix evaluation */
                    TopValue = TopStackNode->Val;
                    
                    /* pop the value and then the prefix operator - assume they'll still be there until we're done */
                    *StackTop = TopOperatorNode->Next;
                    HeapPopStack(TopOperatorNode, sizeof(struct ExpressionStack)*2 + TypeStackSizeValue(TopValue));
                    
                    /* do the prefix operation */
                    ExpressionPrefixOperator(Parser, StackTop, TopOperatorNode->Op, TopValue);
                    break;
                
                case OrderPostfix:
                    /* postfix evaluation */
                    TopValue = TopStackNode->Next->Val;
                    
                    /* pop the prefix operator and then the value - assume they'll still be there until we're done */
                    *StackTop = TopStackNode->Next->Next;
                    HeapPopStack(TopOperatorNode, sizeof(struct ExpressionStack)*2 + TypeStackSizeValue(TopValue));

                    /* do the postfix operation */
                    ExpressionPostfixOperator(Parser, StackTop, TopOperatorNode->Op, TopValue);
                    break;
                
                case OrderInfix:
                    /* infix evaluation */
                    TopValue = TopStackNode->Val;
                    BottomValue = TopOperatorNode->Next->Val;
                    
                    /* pop a value, the operator and another value */
                    HeapPopStack(TopOperatorNode, sizeof(struct ExpressionStack)*3 + TypeStackSizeValue(TopValue) + TypeStackSizeValue(BottomValue));

                    /* do the infix operation */
                    ExpressionInfixOperator(Parser, StackTop, TopOperatorNode->Op, BottomValue, TopValue);
                    break;

                case OrderNone:
                    break;
            }
        }
    }
}

/* push an operator on to the expression stack */
void ExpressionStackPushOperator(struct ParseState *Parser, struct ExpressionStack **StackTop, enum OperatorOrder Order, enum LexToken Token, int Precedence)
{
    struct ExpressionStack *StackNode = VariableAlloc(Parser, sizeof(struct ExpressionStack), FALSE);
    StackNode->Next = *StackTop;
    StackNode->Order = Order;
    StackNode->Op = Token;
    StackNode->Precedence = Precedence;
    *StackTop = StackNode;
}

/* parse an expression with operator precedence */
int ExpressionParse(struct ParseState *Parser, struct Value **Result)
{
    struct Value *LexValue;
    int PrefixState = TRUE;
    int Done = FALSE;
    int BracketPrecedence = 0;
    int LocalPrecedence;
    int Precedence = 0;
    struct ExpressionStack *StackTop = NULL;
    
    do
    {
        struct ParseState PreState = *Parser;
        enum LexToken Token = LexGetToken(Parser, &LexValue, TRUE);
        if ((int)Token <= (int)TokenCloseBracket)
        { /* it's an operator with precedence */
            if (PrefixState)
            { /* expect a prefix operator */
                if (OperatorPrecedence[(int)Token].PrefixPrecedence == 0)
                    ProgramFail(Parser, "operator not expected here");
                
                if (Parser->Mode == RunModeRun)
                {   
                    LocalPrecedence = OperatorPrecedence[(int)Token].PrefixPrecedence;
                    Precedence = BracketPrecedence + LocalPrecedence;
                    if (Token == TokenOpenBracket || Token == TokenLeftSquareBracket)
                    { /* boost the bracket operator precedence, then push */
                        BracketPrecedence += BRACKET_PRECEDENCE;
                        ExpressionStackPushOperator(Parser, &StackTop, OrderPrefix, Token, Precedence);
                    }
                    else
                    { /* scan and collapse the stack to the precedence of this operator, then push */
                        ExpressionStackCollapse(Parser, &StackTop, Precedence);
                        ExpressionStackPushOperator(Parser, &StackTop, OrderPrefix, Token, Precedence);
                    }
                }
            }
            else
            { /* expect an infix or postfix operator */
                if (OperatorPrecedence[(int)Token].PostfixPrecedence != 0)
                {
                    switch (Token)
                    {
                        case TokenCloseBracket:
                            if (BracketPrecedence == 0)
                            { /* assume this bracket is after the end of the expression */
                                Done = TRUE;
                            }
                            else
                                BracketPrecedence -= BRACKET_PRECEDENCE;
                            break;
                    
                        case TokenRightSquareBracket:
                            if (BracketPrecedence == 0)
                                ProgramFail(Parser, "no matching open square bracket");

                            /* scan and collapse the stack to bracket precedence */
                            ExpressionStackCollapse(Parser, &StackTop, BracketPrecedence);
                            BracketPrecedence -= BRACKET_PRECEDENCE;
                            
                            /* apply the array index operator */
                            // XXX
                            break;

                        default:
                            /* scan and collapse the stack to the precedence of this operator, then push */
                            Precedence = BracketPrecedence + OperatorPrecedence[(int)Token].PostfixPrecedence;
                            ExpressionStackCollapse(Parser, &StackTop, Precedence);
                            ExpressionStackPushOperator(Parser, &StackTop, OrderPostfix, Token, Precedence);
                            break;
                    }
                }
                else if (OperatorPrecedence[(int)Token].InfixPrecedence != 0)
                { /* scan and collapse the stack, then push */
                    Precedence = BracketPrecedence + OperatorPrecedence[(int)Token].InfixPrecedence;
                    
                    /* for right to left order, only go down to the next higher precedence so we evaluate it in reverse order */
                    /* for left to right order, collapse down to this precedence so we evaluate it in forward order */
                    if (IS_LEFT_TO_RIGHT(Precedence))
                        ExpressionStackCollapse(Parser, &StackTop, Precedence);
                    else
                        ExpressionStackCollapse(Parser, &StackTop, Precedence+1);

                    ExpressionStackPushOperator(Parser, &StackTop, OrderInfix, Token, Precedence);
                    PrefixState = TRUE;
                }
                else
                    ProgramFail(Parser, "operator not expected here");
            }
        }
        else if (Token == TokenIdentifier)
        { /* it's a variable, function or a macro */
            if (LexGetToken(Parser, NULL, FALSE) == TokenOpenBracket)
                ExpressionParseFunctionCall(Parser, &StackTop, LexValue->Val->Identifier);
            else
            {
                if (Parser->Mode == RunModeRun)
                {
                    struct Value *VariableValue = NULL;
                    
                    VariableGet(Parser, LexValue->Val->Identifier, &VariableValue);
                    if (VariableValue->Typ->Base == TypeMacro)
                    {
                        ProgramFail(Parser, "XXX macros unimplemented");
#if 0
                        struct ParseState MacroParser = VariableValue->Val->Parser;
                        
                        if (!ExpressionParse(&MacroParser, Result) || LexGetToken(&MacroParser, NULL, FALSE) != TokenEndOfFunction)
                            ProgramFail(&MacroParser, "expression expected");
#endif
                    }
                    else if (VariableValue->Typ == TypeVoid)
                        ProgramFail(Parser, "a void value isn't much use here");
                    else
                    { /* it's a value variable */
                        ExpressionStackPushValue(Parser, &StackTop, VariableValue);
                    }
                }
                else /* push a dummy value */
                    ExpressionStackPushValueByType(Parser, &StackTop, &VoidType);
            }
        }
        else if ((int)Token <= (int)TokenCharacterConstant)
        { /* it's a value of some sort, push it */
            if (!PrefixState)
                ProgramFail(Parser, "value not expected here");
                
            PrefixState = FALSE;
            ExpressionStackPushValue(Parser, &StackTop, LexValue);
        }
        else
        { /* it isn't a token from an expression */
            *Parser = PreState;
            Done = TRUE;
        }
        
    } while (!Done);
    
    /* scan and collapse the stack to precedence 0 */
    ExpressionStackCollapse(Parser, &StackTop, 0);
    
    /* fix up the stack and return the result if we're in run mode */
    if (StackTop != NULL)
    {
        /* all that should be left is a single value on the stack */
        if (Parser->Mode == RunModeRun)
            *Result = StackTop->Val;

        HeapPopStack(StackTop, sizeof(struct ExpressionStack));
    }
    
    return TRUE;
}


/* do a function call */
void ExpressionParseFunctionCall(struct ParseState *Parser, struct ExpressionStack **StackTop, const char *FuncName)
{
    struct Value *ReturnValue;
    struct Value *FuncValue;
    struct Value *Param;
    struct Value **ParamArray = NULL;
    int ArgCount;
    enum LexToken Token = LexGetToken(Parser, NULL, TRUE);    /* open bracket */
    
    if (Parser->Mode == RunModeRun) 
    { /* get the function definition */
        VariableGet(Parser, FuncName, &FuncValue);
        if (FuncValue->Typ->Base != TypeFunction)
            ProgramFail(Parser, "not a function - can't call");
    
        ExpressionStackPushValueByType(Parser, StackTop, FuncValue->Val->FuncDef.ReturnType);
        ReturnValue = (*StackTop)->Val;
        HeapPushStackFrame();
        ParamArray = HeapAllocStack(sizeof(struct Value *) * FuncValue->Val->FuncDef.NumParams);
        if (ParamArray == NULL)
            ProgramFail(Parser, "out of memory");
    }
        
    /* parse arguments */
    ArgCount = 0;
    do {
        if (ExpressionParse(Parser, &Param))
        {
            if (Parser->Mode == RunModeRun)
            { 
                if (ArgCount >= FuncValue->Val->FuncDef.NumParams)
                {
                    if (!FuncValue->Val->FuncDef.VarArgs)
                        ProgramFail(Parser, "too many arguments to %s()", FuncName);
                }
                else
                {
                    if (FuncValue->Val->FuncDef.ParamType[ArgCount] != Param->Typ)
                        ProgramFail(Parser, "parameter %d to %s() is the wrong type", ArgCount+1, FuncName);
                }
                
                if (ArgCount < FuncValue->Val->FuncDef.NumParams)
                    ParamArray[ArgCount] = Param;
            }
            
            ArgCount++;
            Token = LexGetToken(Parser, NULL, TRUE);
            if (Token != TokenComma && Token != TokenCloseBracket)
                ProgramFail(Parser, "comma expected");
        }
        else
        { /* end of argument list? */
            Token = LexGetToken(Parser, NULL, TRUE);
            if (!TokenCloseBracket)
                ProgramFail(Parser, "bad argument");
        }
    } while (Token != TokenCloseBracket);
    
    if (Parser->Mode == RunModeRun) 
    { /* run the function */
        if (ArgCount < FuncValue->Val->FuncDef.NumParams)
            ProgramFail(Parser, "not enough arguments to '%s'", FuncName);
        
        if (FuncValue->Val->FuncDef.Intrinsic == NULL)
        { /* run a user-defined function */
            struct ParseState FuncParser = FuncValue->Val->FuncDef.Body;
            int Count;
            
            VariableStackFrameAdd(Parser, FuncValue->Val->FuncDef.Intrinsic ? FuncValue->Val->FuncDef.NumParams : 0);
            TopStackFrame->NumParams = ArgCount;
            TopStackFrame->ReturnValue = ReturnValue;
            for (Count = 0; Count < FuncValue->Val->FuncDef.NumParams; Count++)
                VariableDefine(Parser, FuncValue->Val->FuncDef.ParamName[Count], ParamArray[Count]);
                
            if (!ParseStatement(&FuncParser))
                ProgramFail(&FuncParser, "function body expected");
        
            if (FuncValue->Val->FuncDef.ReturnType != ReturnValue->Typ)
                ProgramFail(&FuncParser, "bad type of return value");

            VariableStackFramePop(Parser);
        }
        else
            FuncValue->Val->FuncDef.Intrinsic(Parser, ReturnValue, ParamArray, ArgCount);

        HeapPopStackFrame();
    }
}
#endif

/* parse an expression. operator precedence is not supported */
int ExpressionParseInt(struct ParseState *Parser)
{
    struct Value *Val;
    int Result = 0;
    
    if (!ExpressionParse(Parser, &Val))
        ProgramFail(Parser, "expression expected");
    
    if (Parser->Mode == RunModeRun)
    { 
        if (Val->Typ->Base != TypeInt)
            ProgramFail(Parser, "integer value expected");
    
        Result = Val->Val->Integer;
        VariableStackPop(Parser, Val);
    }
    
    return Result;
}