elks-enhanced - XT-Emporium

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/* ---------------------------------------------------------------------------
 * Basic Interpreter
 * Robin Edwards 2014
 * ---------------------------------------------------------------------------
 * This BASIC is modelled on Sinclair BASIC for the ZX81 and ZX Spectrum. It
 * should be capable of running most of the examples in the manual for both
 * machines, with the exception of anything machine specific (i.e. graphics,
 * sound & system variables).
 *
 * Notes
 *  - All numbers (except line numbers) are floats internally
 *  - Multiple commands are allowed per line, seperated by :
 *  - LET is optional e.g. LET a = 6: b = 7
 *  - MOD provides the modulo operator which was missing from Sinclair BASIC.
 *     Both numbers are first rounded to ints e.g. 5 mod 2 = 1
 *  - CONT can be used to continue from a STOP. It does not continue from any
 *     other error condition.
 *  - Arrays can be any dimension. There is no single char limit to names.
 *  - Like Sinclair BASIC, DIM a(10) and LET a = 5 refer to different 'a's.
 *     One is a simple variable, the other is an array. There is no ambiguity
 *     since the one being referred to is always clear from the context.
 *  - String arrays differ from Sinclair BASIC. DIM a$(5,5) makes an array
 *     of 25 strings, which can be any length. e.g. LET a$(1,1)="long string"
 *  - functions like LEN, require brackets e.g. LEN(a$)
 *  - String manipulation functions are LEFT$, MID$, RIGHT$
 *  - RND is a nonary operator not a function i.e. RND not RND()
 *  - PRINT AT x,y ... is replaced by POSITION x,y : PRINT ...
 *  - LIST takes an optional start and end e.g. LIST 1,100 or LIST 50
 *  - INKEY$ reads the last key pressed from the keyboard, or an empty string
 *     if no key pressed. The (single key) buffer is emptied after the call.
 *     e.g. a$ = INKEY$
 *  - LOAD/SAVE load and save the current program to the EEPROM (1k limit).
 *     SAVE+ will set the auto-run flag, which loads the program automatically
 *     on boot. With a filename e.g. SAVE "test" saves to an external EEPROM.
 *  - DIR/DELETE "filename" - list and remove files from external EEPROM.
 *  - PINMODE <pin>, <mode> - sets the pin mode (0=input, 1=output, 2=pullup)
 *  - PIN <pin>, <state> - sets the pin high (non zero) or low (zero)
 *  - PINREAD(pin) returns pin value, ANALOGRD(pin) for analog pins
 * ---------------------------------------------------------------------------
 *
 * From Arduino BASIC https://github.com/robinhedwards/ArduinoBASIC
 * Apr 2022 ported to Linux, macOS & ELKS Greg Haerr
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <float.h>
#include <limits.h>
#include <math.h>

#include "host.h"
#include "basic.h"

int sysPROGEND;
int sysSTACKSTART, sysSTACKEND;
int sysVARSTART, sysVAREND;
int sysGOSUBSTART, sysGOSUBEND;

const char string_0[] PROGMEM = "OK";
const char string_1[] PROGMEM = "Bad number";
const char string_2[] PROGMEM = "Line too long";
const char string_3[] PROGMEM = "Unexpected input";
const char string_4[] PROGMEM = "Unterminated string";
const char string_5[] PROGMEM = "Missing bracket";
const char string_6[] PROGMEM = "Error in expr";
const char string_7[] PROGMEM = "Numeric expr expected";
const char string_8[] PROGMEM = "String expr expected";
const char string_9[] PROGMEM = "Line number too big";
const char string_10[] PROGMEM = "Out of memory";
const char string_11[] PROGMEM = "Div by zero";
const char string_12[] PROGMEM = "Variable not found";
const char string_13[] PROGMEM = "Bad command";
const char string_14[] PROGMEM = "Bad line number";
const char string_15[] PROGMEM = "Break pressed";
const char string_16[] PROGMEM = "NEXT without FOR";
const char string_17[] PROGMEM = "STOP statement";
const char string_18[] PROGMEM = "Missing THEN in IF";
const char string_19[] PROGMEM = "RETURN without GOSUB";
const char string_20[] PROGMEM = "Wrong array dims";
const char string_21[] PROGMEM = "Bad array index";
const char string_22[] PROGMEM = "Bad string index";
const char string_23[] PROGMEM = "Error in VAL input";
const char string_24[] PROGMEM = "Bad parameter";
const char string_25[] PROGMEM = "End of file";
const char string_26[] PROGMEM = "File error";
const char string_27[] PROGMEM = "Function not builtin";
const char string_28[] PROGMEM = "Wrong number of function arguments";
const char string_29[] PROGMEM = "No DATA for READ";

const char* const errorTable[] PROGMEM = {
    string_0, string_1, string_2, string_3,
    string_4, string_5, string_6, string_7,
    string_8, string_9, string_10, string_11,
    string_12, string_13, string_14, string_15,
    string_16, string_17, string_18, string_19,
    string_20, string_21, string_22, string_23,
    string_24, string_25, string_26, string_27,
    string_28, string_29
};

// Token flags
// bits 1+2 number of arguments
#define TKN_ARGS_NUM_MASK	0x03
// bit 3 return type (set if string)
#define TKN_RET_TYPE_STR	0x04
// bits 4-6 argument type (set if string)
#define TKN_ARG1_TYPE_STR	0x08
#define TKN_ARG2_TYPE_STR	0x10
#define TKN_ARG3_TYPE_STR	0x20

#define TKN_ARG_MASK		0x38
#define TKN_ARG_SHIFT		3
// bits 7,8 formatting
#define TKN_FMT_POST		0x40
#define TKN_FMT_PRE		0x80


PROGMEM const TokenTableEntry tokenTable[] = {
    {0, 0}, {0, 0}, {0, 0}, {0, 0},
    {0, 0}, {0, 0}, {0, 0}, {0, 0},
    {"(", 0},
    {")",0},
    {"+",0},
    {"-",0},
    {"*",0},
    {"/",0},
    {"=",0},
    {">",0},
    {"<",0},
    {"<>",0},
    {">=",0},
    {"<=",0},
    {":",TKN_FMT_POST},
    {";",0},
    {",",0},
    {"AND",TKN_FMT_PRE|TKN_FMT_POST},
    {"OR",TKN_FMT_PRE|TKN_FMT_POST},
    {"NOT",TKN_FMT_POST},
    {"PRINT",TKN_FMT_POST},
    {"LET",TKN_FMT_POST},
    {"LIST",TKN_FMT_POST},
    {"RUN",TKN_FMT_POST},
    {"GOTO",TKN_FMT_POST},
    {"REM",TKN_FMT_POST},
    {"STOP",TKN_FMT_POST},
    {"INPUT",TKN_FMT_POST},
    {"CONT",TKN_FMT_POST},
    {"IF",TKN_FMT_POST},
    {"THEN",TKN_FMT_PRE|TKN_FMT_POST},
    {"LEN",1|TKN_ARG1_TYPE_STR},
    {"VAL",1|TKN_ARG1_TYPE_STR},
    {"RND",0},
    {"INT",1},
    {"STR$",1|TKN_RET_TYPE_STR},
    {"FOR",TKN_FMT_POST},
    {"TO",TKN_FMT_PRE|TKN_FMT_POST},
    {"STEP",TKN_FMT_PRE|TKN_FMT_POST},
    {"NEXT", TKN_FMT_POST},
    {"MOD",TKN_FMT_PRE|TKN_FMT_POST},
    {"NEW",TKN_FMT_POST},
    {"GOSUB",TKN_FMT_POST},
    {"RETURN",TKN_FMT_POST},
    {"DIM",TKN_FMT_POST},
    {"LEFT$",2|TKN_ARG1_TYPE_STR|TKN_RET_TYPE_STR},
    {"RIGHT$",2|TKN_ARG1_TYPE_STR|TKN_RET_TYPE_STR},
    {"MID$",3|TKN_ARG1_TYPE_STR|TKN_RET_TYPE_STR},
    {"CLS",TKN_FMT_POST},
    {"PAUSE",TKN_FMT_POST},
    {"POSITION",TKN_FMT_POST},
    {"PIN",TKN_FMT_POST},
    {"PINMODE",TKN_FMT_POST},
    {"INKEY$",0},
    {"SAVE",TKN_FMT_POST},
    {"LOAD",TKN_FMT_POST},
    {"PINREAD",1},
    {"ANALOGRD",1},
    {"DIR",TKN_FMT_POST},
    {"DELETE",TKN_FMT_POST},
    {"PI",0},
    {"ABS",1},
    {"COS",1},
    {"SIN",1},
    {"TAN",1},
    {"ACS",1},
    {"ASN",1},
    {"ATN",1},
    {"EXP",1},
    {"LN",1},
    {"POW",2},
    {"CHR$",1|TKN_RET_TYPE_STR},
    {"CODE",1|TKN_ARG1_TYPE_STR},
    {"DATA",TKN_FMT_POST},
    {"READ",TKN_FMT_POST},
    {"RESTORE",TKN_FMT_POST},
    {"MODE",TKN_FMT_POST},
    {"COLOR",TKN_FMT_POST},
    {"PLOT",TKN_FMT_POST},
    {"DRAW",TKN_FMT_POST},
    {"CIRCLE",TKN_FMT_POST},
    {"INPB", 1},
    {"INPW", 1},
    {"OUTB", TKN_FMT_POST},
    {"OUTW", TKN_FMT_POST},
    {"HEX$",1|TKN_RET_TYPE_STR},
    {"PEEK", 2},
    {"POKE", TKN_FMT_POST},
};


/* **************************************************************************
 * PROGRAM FUNCTIONS
 * **************************************************************************/
void printTokens(unsigned char *p) {
    int modeREM = 0;
    while (*p != TOKEN_EOL) {
        if (*p == TOKEN_IDENT) {
            p++;
            while (*p < 0x80)
                host_outputChar(*p++);
            host_outputChar((*p++)-0x80);
        }
        else if (*p == TOKEN_NUMBER) {
            p++;
            host_outputFloat(*(float*)p);
            p+=sizeof(float);
        }
        else if (*p == TOKEN_INTEGER) {
            p++;
            host_outputLong(*(long*)p);
            p+=sizeof(long);
        }
        else if (*p == TOKEN_STRING) {
            p++;
            if (modeREM) {
                host_outputString((char*)p);
                p+=1 + strlen((char*)p);
            }
            else {
                host_outputChar('\"');
                while (*p) {
                    if (*p == '\"') host_outputChar('\"');
                    host_outputChar(*p++);
                }
                host_outputChar('\"');
                p++;
            }
        }
        else {
            uint8_t fmt = pgm_read_byte_near(tokenTable[*p].format);
            if (fmt & TKN_FMT_PRE)
                host_outputChar(' ');
            host_outputString(pgm_read_word(tokenTable[*p].token));
            if (fmt & TKN_FMT_POST)
                host_outputChar(' ');
            if (*p==TOKEN_REM)
                modeREM = 1;
            p++;
        }
    }
}

void listProg(uint16_t first, uint16_t last) {
    unsigned char *p = &mem[0];
    while (p < &mem[sysPROGEND]) {
        uint16_t lineNum = *(uint16_t*)(p+2);
        if ((!first || lineNum >= first) && (!last || lineNum <= last)) {
            host_outputLong(lineNum);
            host_outputChar(' ');
            printTokens(p+4);
            host_newLine();
        }
        p+= *(uint16_t *)p;
    }
}

unsigned char *findProgLine(uint16_t targetLineNumber) {
    unsigned char *p = &mem[0];
    while (p < &mem[sysPROGEND]) {
        uint16_t lineNum = *(uint16_t*)(p+2);
        if (lineNum >= targetLineNumber)
            break;
        p+= *(uint16_t *)p;
    }
    return p;
}

void deleteProgLine(unsigned char *p) {
    uint16_t lineLen = *(uint16_t*)p;
    sysPROGEND -= lineLen;
    memmove(p, p+lineLen, &mem[sysPROGEND] - p);
}

int doProgLine(uint16_t lineNumber, unsigned char* tokenPtr, int tokensLength)
{
    // find line of the at or immediately after the number
    unsigned char *p = findProgLine(lineNumber);
    uint16_t foundLine = 0;
    if (p < &mem[sysPROGEND])
        foundLine = *(uint16_t*)(p+2);
    // if there's a line matching this one - delete it
    if (foundLine == lineNumber)
        deleteProgLine(p);
    // now check to see if this is an empty line, if so don't insert it
    if (*tokenPtr == TOKEN_EOL)
        return 1;
    // we now need to insert the new line at p
    int bytesNeeded = 4 + tokensLength;	// length, linenum + tokens
    if (sysPROGEND + bytesNeeded > sysVARSTART)
        return 0;
    // make room if this isn't the last line
    if (foundLine)
        memmove(p + bytesNeeded, p, &mem[sysPROGEND] - p);
    *(uint16_t *)p = bytesNeeded; 
    p += 2;
    *(uint16_t *)p = lineNumber; 
    p += 2;
    memcpy(p, tokenPtr, tokensLength);
    sysPROGEND += bytesNeeded;
    return 1;
}

/* **************************************************************************
 * CALCULATOR STACK FUNCTIONS
 * **************************************************************************/

// Calculator stack starts at the start of memory after the program
// and grows towards the end
// contains either floats or null-terminated strings with the length on the end

int stackPushNum(float val) {
    if (sysSTACKEND + sizeof(float) > sysVARSTART)
        return 0;	// out of memory
    unsigned char *p = &mem[sysSTACKEND];
    *(float *)p = val;
    sysSTACKEND += sizeof(float);
    return 1;
}
float stackPopNum() {
    sysSTACKEND -= sizeof(float);
    unsigned char *p = &mem[sysSTACKEND];
    return *(float *)p;
}
int stackPushStr(char *str) {
    int len = 1 + strlen(str);
    if (sysSTACKEND + len + 2 > sysVARSTART)
        return 0;	// out of memory
    unsigned char *p = &mem[sysSTACKEND];
    strcpy((char*)p, str);
    p += len;
    *(uint16_t *)p = len;
    sysSTACKEND += len + 2;
    return 1;
}
char *stackGetStr() {
    // returns string without popping it
    unsigned char *p = &mem[sysSTACKEND];
    int len = *(uint16_t *)(p-2);
    return (char *)(p-len-2);
}
char *stackPopStr() {
    unsigned char *p = &mem[sysSTACKEND];
    int len = *(uint16_t *)(p-2);
    sysSTACKEND -= (len+2);
    return (char *)&mem[sysSTACKEND];
}

void stackAdd2Strs() {
    // equivalent to popping 2 strings, concatenating them and pushing the result
    unsigned char *p = &mem[sysSTACKEND];
    int str2len = *(uint16_t *)(p-2);
    sysSTACKEND -= (str2len+2);
    char *str2 = (char*)&mem[sysSTACKEND];
    p = &mem[sysSTACKEND];
    int str1len = *(uint16_t *)(p-2);
    sysSTACKEND -= (str1len+2);
    char *str1 = (char*)&mem[sysSTACKEND];
    p = &mem[sysSTACKEND];
    // shift the second string up (overwriting the null terminator of the first string)
    memmove(str1 + str1len - 1, str2, str2len);
    // write the length and update stackend
    int newLen = str1len + str2len - 1;
    p += newLen;
    *(uint16_t *)p = newLen;
    sysSTACKEND += newLen + 2;
}

// mode 0 = LEFT$, 1 = RIGHT$
void stackLeftOrRightStr(int len, int mode) {
    // equivalent to popping the current string, doing the operation then pushing it again
    unsigned char *p = &mem[sysSTACKEND];
    int strlen = *(uint16_t *)(p-2);
    len++; // include trailing null
    if (len > strlen) len = strlen;
    if (len == strlen) return;	// nothing to do
    sysSTACKEND -= (strlen+2);
    p = &mem[sysSTACKEND];
    if (mode == 0) {
        // truncate the string on the stack
        *(p+len-1) = 0;
    }
    else {
        // copy the rightmost characters
        memmove(p, p + strlen - len, len);
    }
    // write the length and update stackend
    p += len;
    *(uint16_t *)p = len;
    sysSTACKEND += len + 2;
}

void stackMidStr(int start, int len) {
    // equivalent to popping the current string, doing the operation then pushing it again
    unsigned char *p = &mem[sysSTACKEND];
    int strlen = *(uint16_t *)(p-2);
    len++; // include trailing null
    if (start > strlen) start = strlen;
    start--;	// basic strings start at 1
    if (start + len > strlen) len = strlen - start;
    if (len == strlen) return;	// nothing to do
    sysSTACKEND -= (strlen+2);
    p = &mem[sysSTACKEND];
    // copy the characters
    memmove(p, p + start, len-1);
    *(p+len-1) = 0;
    // write the length and update stackend
    p += len;
    *(uint16_t *)p = len;
    sysSTACKEND += len + 2;
}

/* **************************************************************************
 * VARIABLE TABLE FUNCTIONS
 * **************************************************************************/

// Variable table starts at the end of memory and grows towards the start
// Simple variable
// table +--------+-------+-----------------+-----------------+ . . .
//  <--- | len    | type  | name            | value           |
// grows | 2bytes | 1byte | null terminated | float/string    | 
//       +--------+-------+-----------------+-----------------+ . . .
//
// Array
// +--------+-------+-----------------+----------+-------+ . . .+-------+-------------+. . 
// | len    | type  | name            | num dims | dim1  |      | dimN  | elem(1,..1) |
// | 2bytes | 1byte | null terminated | 2bytes   | 2bytes|      | 2bytes| float       |
// +--------+-------+-----------------+----------+-------+ . . .+-------+-------------+. . 

// variable type byte
#define VAR_TYPE_NUM		0x1
#define VAR_TYPE_FORNEXT	0x2
#define VAR_TYPE_NUM_ARRAY	0x4
#define VAR_TYPE_STRING		0x8
#define VAR_TYPE_STR_ARRAY	0x10

unsigned char *findVariable(char *searchName, int searchMask) {
    unsigned char *p = &mem[sysVARSTART];
    while (p < &mem[sysVAREND]) {
        int type = *(p+2);
        if (type & searchMask) {
            unsigned char *name = p+3;
            if (strcmp((char*)name, searchName) == 0)
                return p;
        }
        p+= *(uint16_t *)p;
    }
    return NULL;
}

void deleteVariableAt(unsigned char *pos) {
    int len = *(uint16_t *)pos;
    if (pos == &mem[sysVARSTART]) {
        sysVARSTART += len;
        return;
    }
    memmove(&mem[sysVARSTART] + len, &mem[sysVARSTART], pos - &mem[sysVARSTART]);
    sysVARSTART += len;
}

// todo - consistently return errors rather than 1 or 0?

int storeNumVariable(char *name, float val) {
    // these can be modified in place
    int nameLen = strlen(name);
    unsigned char *p = findVariable(name, VAR_TYPE_NUM|VAR_TYPE_FORNEXT);
    if (p != NULL)
    {	// replace the old value
        // (could either be VAR_TYPE_NUM or VAR_TYPE_FORNEXT)
        p += 3;	// len + type;
        p += nameLen + 1;
        *(float *)p = val;
    }
    else
    {	// allocate a new variable
        int bytesNeeded = 3;	// len + flags
        bytesNeeded += nameLen + 1;	// name
        bytesNeeded += sizeof(float);	// val

        if (sysVARSTART - bytesNeeded < sysSTACKEND)
            return 0;	// out of memory
        sysVARSTART -= bytesNeeded;

        unsigned char *p = &mem[sysVARSTART];
        *(uint16_t *)p = bytesNeeded; 
        p += 2;
        *p++ = VAR_TYPE_NUM;
        strcpy((char*)p, name); 
        p += nameLen + 1;
        *(float *)p = val;
    }
    return 1;
}

int storeForNextVariable(char *name, float start, float step, float end, uint16_t lineNum, uint16_t stmtNum) {
    int nameLen = strlen(name);
    int bytesNeeded = 3;	// len + flags
    bytesNeeded += nameLen + 1;	// name
    bytesNeeded += 3 * sizeof(float);	// vals
    bytesNeeded += 2 * sizeof(uint16_t);

    // unlike simple numeric variables, these are reallocated if they already exist
    // since the existing value might be a simple variable or a for/next variable
    unsigned char *p = findVariable(name, VAR_TYPE_NUM|VAR_TYPE_FORNEXT);
    if (p != NULL) {
        // check there will actually be room for the new value
        uint16_t oldVarLen = *(uint16_t*)p;
        if (sysVARSTART - (bytesNeeded - oldVarLen) < sysSTACKEND)
            return 0;	// not enough memory
        deleteVariableAt(p);
    }

    if (sysVARSTART - bytesNeeded < sysSTACKEND)
        return 0;	// out of memory
    sysVARSTART -= bytesNeeded;

    p = &mem[sysVARSTART];
    *(uint16_t *)p = bytesNeeded; 
    p += 2;
    *p++ = VAR_TYPE_FORNEXT;
    strcpy((char*)p, name); 
    p += nameLen + 1;
    *(float *)p = start; 
    p += sizeof(float);
    *(float *)p = step; 
    p += sizeof(float);
    *(float *)p = end; 
    p += sizeof(float);
    *(uint16_t *)p = lineNum; 
    p += sizeof(uint16_t);
    *(uint16_t *)p = stmtNum;
    return 1;
}

int storeStrVariable(char *name, char *val) {
    int nameLen = strlen(name);
    int valLen = strlen(val);
    int bytesNeeded = 3;	// len + type
    bytesNeeded += nameLen + 1;	// name
    bytesNeeded += valLen + 1;	// val

    // strings and arrays are re-allocated if they already exist
    unsigned char *p = findVariable(name, VAR_TYPE_STRING);
    if (p != NULL) {
        // check there will actually be room for the new value
        uint16_t oldVarLen = *(uint16_t*)p;
        if (sysVARSTART - (bytesNeeded - oldVarLen) < sysSTACKEND)
            return 0;	// not enough memory
        deleteVariableAt(p);
    }

    if (sysVARSTART - bytesNeeded < sysSTACKEND)
        return 0;	// out of memory
    sysVARSTART -= bytesNeeded;

    p = &mem[sysVARSTART];
    *(uint16_t *)p = bytesNeeded; 
    p += 2;
    *p++ = VAR_TYPE_STRING;
    strcpy((char*)p, name); 
    p += nameLen + 1;
    strcpy((char*)p, val);
    return 1;
}

int createArray(char *name, int isString) {
    // dimensions and number of dimensions on the calculator stack
    int nameLen = strlen(name);
    int bytesNeeded = 3;	// len + flags
    bytesNeeded += nameLen + 1;	// name
    bytesNeeded += 2;		// num dims
    int numElements = 1;
    int numDims = (int)stackPopNum();
    // keep the current stack position, since we'll need to pop these values again
    int oldSTACKEND = sysSTACKEND;	
    for (int i=0; i<numDims; i++) {
        int dim = (int)stackPopNum();
        numElements *= dim;
    }
    bytesNeeded += 2 * numDims + (isString ? 1 : sizeof(float)) * numElements;
    // strings and arrays are re-allocated if they already exist
    unsigned char *p = findVariable(name, (isString ? VAR_TYPE_STR_ARRAY : VAR_TYPE_NUM_ARRAY));
    if (p != NULL) {
        // check there will actually be room for the new value
        uint16_t oldVarLen = *(uint16_t*)p;
        if (sysVARSTART - (bytesNeeded - oldVarLen) < sysSTACKEND)
            return 0;	// not enough memory
        deleteVariableAt(p);
    }

    if (sysVARSTART - bytesNeeded < sysSTACKEND)
        return 0;	// out of memory
    sysVARSTART -= bytesNeeded;

    p = &mem[sysVARSTART];
    *(uint16_t *)p = bytesNeeded; 
    p += 2;
    *p++ = (isString ? VAR_TYPE_STR_ARRAY : VAR_TYPE_NUM_ARRAY);
    strcpy((char*)p, name); 
    p += nameLen + 1;
    *(uint16_t *)p = numDims; 
    p += 2;
    sysSTACKEND = oldSTACKEND;
    for (int i=0; i<numDims; i++) {
        int dim = (int)stackPopNum();
        *(uint16_t *)p = dim; 
        p += 2;
    }
    memset(p, 0, numElements * (isString ? 1 : sizeof(float)));
    return 1;
}

int _getArrayElemOffset(unsigned char **p, int *pOffset) {
    // check for correct dimensionality
    int numArrayDims = *(uint16_t*)*p; 
    *p+=2;
    int numDimsGiven = (int)stackPopNum();
    if (numArrayDims != numDimsGiven)
        return ERROR_WRONG_ARRAY_DIMENSIONS;
    // now lookup the element
    int offset = 0;
    int base = 1;
    for (int i=0; i<numArrayDims; i++) {
        int index = (int)stackPopNum();
        int arrayDim = *(uint16_t*)*p; 
        *p+=2;
        if (index < 1 || index > arrayDim)
            return ERROR_ARRAY_SUBSCRIPT_OUT_RANGE;
        offset += base * (index-1);
        base *= arrayDim;
    }
    *pOffset = offset;
    return 0;
}

int setNumArrayElem(char *name, float val) {
    // each index and number of dimensions on the calculator stack
    unsigned char *p = findVariable(name, VAR_TYPE_NUM_ARRAY);
    if (p == NULL)
        return ERROR_VARIABLE_NOT_FOUND;
    p += 3 + strlen(name) + 1;
    
    int offset;
    int ret = _getArrayElemOffset(&p, &offset);
    if (ret) return ret;
    
    p += sizeof(float)*offset;
    *(float *)p = val;
    return ERROR_NONE;
}

int setStrArrayElem(char *name) {
    // string is top of the stack
    // each index and number of dimensions on the calculator stack

    // keep the current stack position, since we can't overwrite the value string
    int oldSTACKEND = sysSTACKEND;
    // how long is the new value?
    char *newValPtr = stackPopStr();
    int newValLen = strlen(newValPtr);

    unsigned char *p = findVariable(name, VAR_TYPE_STR_ARRAY);
    unsigned char *p1 = p;	// so we can correct the length when done
    if (p == NULL)
        return ERROR_VARIABLE_NOT_FOUND;

    p += 3 + strlen(name) + 1;
    
    int offset;
    int ret = _getArrayElemOffset(&p, &offset);
    if (ret) return ret;
    
    // find the correct element by skipping over null terminators
    int i = 0;
    while (i < offset) {
        if (*p == 0) i++;
        p++;
    }
    int oldValLen = strlen((char*)p);
    int bytesNeeded = newValLen - oldValLen;
    // check if we've got enough room for the new value
    if (sysVARSTART - bytesNeeded < oldSTACKEND)
        return 0;	// out of memory
    // correct the length of the variable
    *(uint16_t*)p1 += bytesNeeded;
    memmove(&mem[sysVARSTART - bytesNeeded], &mem[sysVARSTART], p - &mem[sysVARSTART]);
    // copy in the new value
    strcpy((char*)(p - bytesNeeded), newValPtr);
    sysVARSTART -= bytesNeeded;
    return ERROR_NONE;
}

float lookupNumArrayElem(char *name, int *error) {
    // each index and number of dimensions on the calculator stack
    unsigned char *p = findVariable(name, VAR_TYPE_NUM_ARRAY);
    if (p == NULL) {
        *error = ERROR_VARIABLE_NOT_FOUND;
        return 0.0f;
    }
    p += 3 + strlen(name) + 1;
    
    int offset;
    int ret = _getArrayElemOffset(&p, &offset);
    if (ret) {
        *error = ret;
        return 0.0f;
    }
    p += sizeof(float)*offset;
    return *(float *)p;
}

char *lookupStrArrayElem(char *name, int *error) {
    // each index and number of dimensions on the calculator stack
    unsigned char *p = findVariable(name, VAR_TYPE_STR_ARRAY);
    if (p == NULL) {
        *error = ERROR_VARIABLE_NOT_FOUND;
        return NULL;
    }
    p += 3 + strlen(name) + 1;

    int offset;
    int ret = _getArrayElemOffset(&p, &offset);
    if (ret) {
        *error = ret;
        return NULL;
    }
    // find the correct element by skipping over null terminators
    int i = 0;
    while (i < offset) {
        if (*p == 0) i++;
        p++;
    }
    return (char *)p;
}

float lookupNumVariable(char *name) {
    unsigned char *p = findVariable(name, VAR_TYPE_NUM|VAR_TYPE_FORNEXT);
    if (p == NULL) {
        return FLT_MAX;
    }
    p += 3 + strlen(name) + 1;
    return *(float *)p;
}

char *lookupStrVariable(char *name) {
    unsigned char *p = findVariable(name, VAR_TYPE_STRING);
    if (p == NULL) {
        return NULL;
    }
    p += 3 + strlen(name) + 1;
    return (char *)p;
}

ForNextData lookupForNextVariable(char *name) {
    ForNextData ret;
    unsigned char *p = findVariable(name, VAR_TYPE_NUM|VAR_TYPE_FORNEXT);
    if (p == NULL)
        ret.val = FLT_MAX;
    else if (*(p+2) != VAR_TYPE_FORNEXT)
        ret.step = FLT_MAX;
    else {
        p += 3 + strlen(name) + 1;
        ret.val = *(float *)p; 
        p += sizeof(float);
        ret.step = *(float *)p; 
        p += sizeof(float);
        ret.end = *(float *)p; 
        p += sizeof(float);
        ret.lineNumber = *(uint16_t *)p; 
        p += sizeof(uint16_t);
        ret.stmtNumber = *(uint16_t *)p;
    }
    return ret;
}

/* **************************************************************************
 * GOSUB STACK
 * **************************************************************************/
// gosub stack (if used) is after the variables
int gosubStackPush(int lineNumber,int stmtNumber) {
    int bytesNeeded = 2 * sizeof(uint16_t);
    if (sysVARSTART - bytesNeeded < sysSTACKEND)
        return 0;	// out of memory
    // shift the variable table
    memmove(&mem[sysVARSTART]-bytesNeeded, &mem[sysVARSTART], sysVAREND-sysVARSTART);
    sysVARSTART -= bytesNeeded;
    sysVAREND -= bytesNeeded;
    // push the return address
    sysGOSUBSTART = sysVAREND;
    uint16_t *p = (uint16_t*)&mem[sysGOSUBSTART];
    *p++ = (uint16_t)lineNumber;
    *p = (uint16_t)stmtNumber;
    return 1;
}

int gosubStackPop(int *lineNumber, int *stmtNumber) {
    if (sysGOSUBSTART == sysGOSUBEND)
        return 0;
    uint16_t *p = (uint16_t*)&mem[sysGOSUBSTART];
    *lineNumber = (int)*p++;
    *stmtNumber = (int)*p;
    int bytesFreed = 2 * sizeof(uint16_t);
    // shift the variable table
    memmove(&mem[sysVARSTART]+bytesFreed, &mem[sysVARSTART], sysVAREND-sysVARSTART);
    sysVARSTART += bytesFreed;
    sysVAREND += bytesFreed;
    sysGOSUBSTART = sysVAREND;
    return 1;
}

/* **************************************************************************
 * LEXER
 * **************************************************************************/

static unsigned char *tokenIn, *tokenOut;
static int tokenOutLeft;

// nextToken returns -1 for end of input, 0 for success, +ve number = error code
int nextToken()
{
    // Skip any whitespace.
    while (isspace(*tokenIn))
        tokenIn++;
    // check for end of line
    if (*tokenIn == 0) {
        *tokenOut++ = TOKEN_EOL;
        tokenOutLeft--;
        return -1;
    }
    // Number: [0-9.]+
    // TODO - handle 1e4 etc
    if (isdigit(*tokenIn) || *tokenIn == '.') {   // Number: [0-9.]+
        int gotDecimal = 0;
        char numStr[MAX_NUMBER_LEN+1];
        int numLen = 0;
        do {
            if (numLen == MAX_NUMBER_LEN) return ERROR_LEXER_BAD_NUM;
            if (*tokenIn == '.') {
                if (gotDecimal) return ERROR_LEXER_BAD_NUM;
                else gotDecimal = 1;
            }
            numStr[numLen++] = *tokenIn++;
        } 
        while (isdigit(*tokenIn) || *tokenIn == '.');

        numStr[numLen] = 0;
        if (tokenOutLeft <= 5) return ERROR_LEXER_TOO_LONG;
        tokenOutLeft -= 5;
        if (!gotDecimal) {
            long val = strtol(numStr, 0, 10);
            if (val == LONG_MAX || val == LONG_MIN)
                gotDecimal = true;
            else {
                *tokenOut++ = TOKEN_INTEGER;
                *(long*)tokenOut = val;
                tokenOut += sizeof(long);
            }
        }
        if (gotDecimal)
        {
            *tokenOut++ = TOKEN_NUMBER;
            *(float*)tokenOut = (float)strtod(numStr, 0);
            tokenOut += sizeof(float);
        }
        return 0;
    }
    // identifier: [a-zA-Z][a-zA-Z0-9]*[$]
    if (isalpha(*tokenIn)) {
        char identStr[MAX_IDENT_LEN+1];
        int identLen = 0;
        identStr[identLen++] = toupper(*tokenIn++); // copy first char
        while (isalnum(*tokenIn) || *tokenIn=='$') {
            if (identLen < MAX_IDENT_LEN)
                identStr[identLen++] = toupper(*tokenIn);
            tokenIn++;
        }
        identStr[identLen] = 0;
        // check to see if this is a keyword
        for (int i = FIRST_IDENT_TOKEN; i <= LAST_IDENT_TOKEN; i++) {
            if (strcmp(identStr, pgm_read_word(tokenTable[i].token)) == 0) {
                if (tokenOutLeft <= 1) return ERROR_LEXER_TOO_LONG;
                tokenOutLeft--;
                *tokenOut++ = i;
                // special case for REM
                if (i == TOKEN_REM) {
                    *tokenOut++ = TOKEN_STRING;
                    // skip whitespace
                    while (isspace(*tokenIn))
                        tokenIn++;
                    // copy the comment
                    while (*tokenIn) {
                        *tokenOut++ = *tokenIn++;
                    }
                    *tokenOut++ = 0;
                }
                return 0;
            }
        }
        // no matching keyword - this must be an identifier
        // $ is only allowed at the end
        char *dollarPos = strchr(identStr, '$');
        if  (dollarPos && dollarPos!= &identStr[0] + identLen - 1) return ERROR_LEXER_UNEXPECTED_INPUT;
        if (tokenOutLeft <= 1+identLen) return ERROR_LEXER_TOO_LONG;
        tokenOutLeft -= 1+identLen;
        *tokenOut++ = TOKEN_IDENT;
        strcpy((char*)tokenOut, identStr);
        tokenOut[identLen-1] |= 0x80;
        tokenOut += identLen;
        return 0;
    }
    // string
    if (*tokenIn=='\"') {
        *tokenOut++ = TOKEN_STRING;
        tokenOutLeft--;
        if (tokenOutLeft <= 1) return ERROR_LEXER_TOO_LONG;
        tokenIn++;
        while (*tokenIn) {
            if (*tokenIn == '\"' && *(tokenIn+1) != '\"')
                break;
            else if (*tokenIn == '\"')
                tokenIn++;
            *tokenOut++ = *tokenIn++;
            tokenOutLeft--;
            if (tokenOutLeft <= 1) return ERROR_LEXER_TOO_LONG;
        }
        if (!*tokenIn) return ERROR_LEXER_UNTERMINATED_STRING;
        tokenIn++;
        *tokenOut++ = 0;
        tokenOutLeft--;
        return 0;
    }
    // handle non-alpha tokens e.g. =
    for (int i=LAST_NON_ALPHA_TOKEN; i>=FIRST_NON_ALPHA_TOKEN; i--) {
        // do this "backwards" so we match >= correctly, not as > then =
        int len = strlen(pgm_read_word(tokenTable[i].token));
        if (strncmp(pgm_read_word(tokenTable[i].token), (char*)tokenIn, len) == 0) {
            if (tokenOutLeft <= 1) return ERROR_LEXER_TOO_LONG;
            *tokenOut++ = i;
            tokenOutLeft--;
            tokenIn += len;
            return 0;
        }
    }
    return ERROR_LEXER_UNEXPECTED_INPUT;
}

int tokenize(unsigned char *input, unsigned char *output, int outputSize)
{
    tokenIn = input;
    tokenOut = output;
    tokenOutLeft = outputSize;
    int ret;
    while (1) {
        ret = nextToken();
        if (ret) break;
    }
    return (ret > 0) ? ret : 0;
}

/* **************************************************************************
 * PARSER / INTERPRETER
 * **************************************************************************/

static char executeMode;	// 0 = syntax check only, 1 = execute
uint16_t lineNumber, stmtNumber;
// stmt number is 0 for the first statement, then increases after each command seperator (:)
// Note that IF a=1 THEN PRINT "x": print "y" is considered to be only 2 statements
static uint16_t jumpLineNumber, jumpStmtNumber;
static uint16_t stopLineNumber, stopStmtNumber;
static uint16_t dataLineNumber;
static char breakCurrentLine;

static unsigned char *tokenBuffer, *prevToken;
static int curToken;
static char identVal[MAX_IDENT_LEN+1];
static char isStrIdent;
static float numVal;
static char *strVal;

int getNextToken()
{
    prevToken = tokenBuffer;
    curToken = *tokenBuffer++;
    if (curToken == TOKEN_IDENT) {
        int i=0;
        while (*tokenBuffer < 0x80)
            identVal[i++] = *tokenBuffer++;
        identVal[i] = (*tokenBuffer++)-0x80;
        isStrIdent = (identVal[i++] == '$');
        identVal[i++] = '\0';
    }
    else if (curToken == TOKEN_NUMBER) {
        numVal = *(float*)tokenBuffer;
        tokenBuffer += sizeof(float);
    }
    else if (curToken == TOKEN_INTEGER) {
        // these are really just for line numbers
        numVal = (float)(*(long*)tokenBuffer);
        tokenBuffer += sizeof(long);
    }
    else if (curToken == TOKEN_STRING) {
        strVal = (char*)tokenBuffer;
        tokenBuffer += 1 + strlen(strVal);
    }
    return curToken;
}

// value (int) returned from parseXXXXX
#define ERROR_MASK						0x0FFF
#define TYPE_MASK						0xF000
#define TYPE_NUMBER						0x0000
#define TYPE_STRING						0x1000

#define IS_TYPE_NUM(x) ((x & TYPE_MASK) == TYPE_NUMBER)
#define IS_TYPE_STR(x) ((x & TYPE_MASK) == TYPE_STRING)

// forward declarations
int parseExpression();
int parsePrimary();
int expectNumber();

// parse a number
int parseNumberExpr()
{
    if (executeMode && !stackPushNum(numVal))
        return ERROR_OUT_OF_MEMORY;
    getNextToken(); // consume the number
    return TYPE_NUMBER;
}

// parse (x1,....xn) e.g. DIM a(10,20)
int parseSubscriptExpr() {
    // stacks x1, .. xn followed by n
    int numDims = 0;
    if (curToken != TOKEN_LBRACKET) return ERROR_EXPR_MISSING_BRACKET;
    getNextToken();
    while(1) {
        numDims++;
        int val = expectNumber();
        if (val) return val;	// error
        if (curToken == TOKEN_RBRACKET)
            break;
        else if (curToken == TOKEN_COMMA)
            getNextToken();
        else
            return ERROR_EXPR_MISSING_BRACKET;
    }
    getNextToken(); // eat )
    if (executeMode && !stackPushNum(numDims))
        return ERROR_OUT_OF_MEMORY;
    return 0;
}

// parse a function call e.g. LEN(a$)
int parseFnCallExpr() {
    int op = curToken;
    int fnSpec = pgm_read_byte_near(tokenTable[curToken].format);
    getNextToken();
    // get the required arguments and types from the token table
    if (curToken != TOKEN_LBRACKET) return ERROR_EXPR_MISSING_BRACKET;
    getNextToken();

    int reqdArgs = fnSpec & TKN_ARGS_NUM_MASK;
    int argTypes = (fnSpec & TKN_ARG_MASK) >> TKN_ARG_SHIFT;
    int ret = (fnSpec & TKN_RET_TYPE_STR) ? TYPE_STRING : TYPE_NUMBER;
    for (int i=0; i<reqdArgs; i++) {
        int val = parseExpression();
        if (val & ERROR_MASK) return val;
        // check we've got the right type
        if (!(argTypes & 1) && !IS_TYPE_NUM(val))
            return ERROR_EXPR_EXPECTED_NUM;
        if ((argTypes & 1) && !IS_TYPE_STR(val))
            return ERROR_EXPR_EXPECTED_STR;
        argTypes >>= 1;
        // if this isn't the last argument, eat the ,
        if (i+1<reqdArgs) {
            if (curToken != TOKEN_COMMA)
                return ERROR_WRONG_NUM_FUNCTION_ARGS;
            getNextToken();
        }
    }
    // now all the arguments will be on the stack (last first)
    if (executeMode) {
        int tmp;
        switch (op) {
        case TOKEN_INT:
            stackPushNum((float)host_floor(stackPopNum()));
            break;
        case TOKEN_ABS:
            {
                float f = stackPopNum();
                if (f < (float)0)
                    f = -f;
                stackPushNum(f);
            }
            break;
        case TOKEN_STR:
            {
                char buf[MAX_NUMBER_LEN+1];
                if (!stackPushStr(host_floatToStr(stackPopNum(), buf)))
                    return ERROR_OUT_OF_MEMORY;
            }
            break;
        case TOKEN_HEX:
            {
                char buf[MAX_NUMBER_LEN+1];
                tmp = (int)host_floor(stackPopNum());
                snprintf(buf, MAX_NUMBER_LEN, "%X", tmp);
                if (!stackPushStr(buf))
                    return ERROR_OUT_OF_MEMORY;
            }
            break;
        case TOKEN_CHR:
            {
                char buf[2];
                buf[0] = (int)stackPopNum();
                buf[1] = '\0';
                if (!stackPushStr(buf))
                    return ERROR_OUT_OF_MEMORY;
            }
            break;
        case TOKEN_LEN:
            tmp = strlen(stackPopStr());
            if (!stackPushNum(tmp)) return ERROR_OUT_OF_MEMORY;
            break;
        case TOKEN_CODE:
            if (!stackPushNum((float)*(unsigned char *)stackPopStr()))
		return ERROR_OUT_OF_MEMORY;
            break;
        case TOKEN_VAL:
            {
                // tokenise str onto the stack
                int oldStackEnd = sysSTACKEND;
                unsigned char *oldTokenBuffer = prevToken;
                int val = tokenize((unsigned char*)stackGetStr(), &mem[sysSTACKEND], sysVARSTART - sysSTACKEND);
                if (val) {
                    if (val == ERROR_LEXER_TOO_LONG) return ERROR_OUT_OF_MEMORY;
                    else return ERROR_IN_VAL_INPUT;
                }
                // set tokenBuffer to point to the new set of tokens on the stack
                tokenBuffer = &mem[sysSTACKEND];
                // move stack end to the end of the new tokens
                sysSTACKEND = tokenOut - &mem[0];
                getNextToken();
                // then parseExpression
                val = parseExpression();
                if (val & ERROR_MASK) {
                    if (val == ERROR_OUT_OF_MEMORY) return val;
                    else return ERROR_IN_VAL_INPUT;
                }
                if (!IS_TYPE_NUM(val))
                    return ERROR_EXPR_EXPECTED_NUM;
                // read the result from the stack
                float f = stackPopNum();
                // pop the tokens from the stack
                sysSTACKEND = oldStackEnd;
                // and pop the original string
                stackPopStr();
                // finally, push the result and set the token buffer back
                stackPushNum(f);
                tokenBuffer = oldTokenBuffer;
                getNextToken();
            }
            break;
        case TOKEN_LEFT:
            tmp = (int)stackPopNum();
            if (tmp < 0) return ERROR_STR_SUBSCRIPT_OUT_RANGE;
            stackLeftOrRightStr(tmp, 0);
            break;
        case TOKEN_RIGHT:
            tmp = (int)stackPopNum();
            if (tmp < 0) return ERROR_STR_SUBSCRIPT_OUT_RANGE;
            stackLeftOrRightStr(tmp, 1);
            break;
        case TOKEN_MID:
            {
                tmp = (int)stackPopNum();
                int start = stackPopNum();
                if (tmp < 0 || start < 1) return ERROR_STR_SUBSCRIPT_OUT_RANGE;
                stackMidStr(start, tmp);
            }
            break;
        case TOKEN_PINREAD:
            tmp = (int)stackPopNum();
            if (!stackPushNum(host_digitalRead(tmp))) return ERROR_OUT_OF_MEMORY;
            break;
        case TOKEN_ANALOGRD:
            tmp = (int)stackPopNum();
            if (!stackPushNum(host_analogRead(tmp))) return ERROR_OUT_OF_MEMORY;
            break;
        case TOKEN_POW:
#if MATH_FUNCTIONS && MATH_INCLUDE_POW
			{
				float y = stackPopNum();
				stackPushNum(POW(stackPopNum(), y));
				break;
			}
#else
            return ERROR_FUNCTION_NOT_BUILTIN;
#endif
        case TOKEN_INPB:
        {
            tmp = (int)stackPopNum();
            if (!stackPushNum(host_inpb(tmp))) return ERROR_OUT_OF_MEMORY;
            break;
        }
        case TOKEN_INPW:
        {
            tmp = (int)stackPopNum();
            if (!stackPushNum(host_inpw(tmp))) return ERROR_OUT_OF_MEMORY;
            break;
        }
        case TOKEN_PEEK:
        {
            int segment = stackPopNum();
            stackPushNum(host_peekb(stackPopNum(), segment));
            break;
        }
        default:
            return ERROR_UNEXPECTED_TOKEN;
        }
    }
    if (curToken != TOKEN_RBRACKET) return ERROR_EXPR_MISSING_BRACKET;
    getNextToken();	// eat )
    return ret;
}

// parse a single argument math function call e.g. COS(a)
int parseMathFn() {
    int op = curToken;
    getNextToken();
    if (curToken != TOKEN_LBRACKET) return ERROR_EXPR_MISSING_BRACKET;
    getNextToken();

    int val = parseExpression();
    if (!IS_TYPE_NUM(val))
        return ERROR_EXPR_EXPECTED_NUM;

    if (executeMode) {
#if MATH_FUNCTIONS
        switch (op) {
        case TOKEN_COS:
            stackPushNum(COS(stackPopNum()));
            break;
        case TOKEN_SIN:
            stackPushNum(SIN(stackPopNum()));
            break;
        case TOKEN_TAN:
            stackPushNum(TAN(stackPopNum()));
            break;
        case TOKEN_ACS:
            stackPushNum(ACOS(stackPopNum()));
            break;
        case TOKEN_ASN:
            stackPushNum(ASIN(stackPopNum()));
            break;
        case TOKEN_ATN:
            stackPushNum(ATAN(stackPopNum()));
            break;
        case TOKEN_EXP:
            stackPushNum(EXP(stackPopNum()));
            break;
        case TOKEN_LN:
            stackPushNum(LOG(stackPopNum()));
            break;
        default:
            return ERROR_UNEXPECTED_TOKEN;
        }
#else
        return ERROR_FUNCTION_NOT_BUILTIN;
#endif
    }
    if (curToken != TOKEN_RBRACKET) return ERROR_EXPR_MISSING_BRACKET;
    getNextToken();	// eat )
    return TYPE_NUMBER;
}

// parse an identifer e.g. a$ or a(5,3)
int parseIdentifierExpr() {
    char ident[MAX_IDENT_LEN+1];
    if (executeMode)
        strcpy(ident, identVal);
    int isStringIdentifier = isStrIdent;
    getNextToken();	// eat ident
    if (curToken == TOKEN_LBRACKET) {
        // array access
        int val = parseSubscriptExpr();
        if (val) return val;
        if (executeMode) {
            if (isStringIdentifier) {
                int error = 0;
                char *str = lookupStrArrayElem(ident, &error);
                if (error) return error;
                else if (!stackPushStr(str)) return ERROR_OUT_OF_MEMORY;
            }
            else {
                int error = 0;
                float f = lookupNumArrayElem(ident, &error);
                if (error) return error;
                else if (!stackPushNum(f)) return ERROR_OUT_OF_MEMORY;
            }
        }
    }
    else {
        // simple variable
        if (executeMode) {
            if (isStringIdentifier) {
                char *str = lookupStrVariable(ident);
                if (!str) return ERROR_VARIABLE_NOT_FOUND;
                else if (!stackPushStr(str)) return ERROR_OUT_OF_MEMORY;
            }
            else {
                float f = lookupNumVariable(ident);
                if (f == FLT_MAX) return ERROR_VARIABLE_NOT_FOUND;
                else if (!stackPushNum(f)) return ERROR_OUT_OF_MEMORY;
            }
        }
    }
    return isStringIdentifier ? TYPE_STRING : TYPE_NUMBER;
}

// parse a string e.g. "hello"
int parseStringExpr() {
    if (executeMode && !stackPushStr(strVal))
        return ERROR_OUT_OF_MEMORY;
    getNextToken(); // consume the string
    return TYPE_STRING;
}

// parse a bracketed expressed e.g. (5+3)
int parseParenExpr() {
    getNextToken();  // eat (
    int val = parseExpression();
    if (val & ERROR_MASK) return val;
    if (curToken != TOKEN_RBRACKET)
        return ERROR_EXPR_MISSING_BRACKET;
    getNextToken();  // eat )
    return val;
}

int parse_PseudoID() {
    int op = curToken;
    getNextToken();
    if (executeMode) {
        switch (op) {
        case TOKEN_RND:
            if (!stackPushNum((float)rand()/(float)RAND_MAX))
                return ERROR_OUT_OF_MEMORY;
            break;
        case TOKEN_PI:
            if (!stackPushNum((float)M_PI))
                return ERROR_OUT_OF_MEMORY;
            break;
        }
    }
    return TYPE_NUMBER;	
}

int parse_INKEY() {
    getNextToken();
    if (executeMode) {
        char str[2];
        str[0] = host_getKey();
        str[1] = 0;
        if (!stackPushStr(str))
            return ERROR_OUT_OF_MEMORY;
    }
    return TYPE_STRING;	
}

int parseUnaryNumExp()
{
    int op = curToken;
    getNextToken();
    int val = parsePrimary();
    if (val & ERROR_MASK) return val;
    if (!IS_TYPE_NUM(val))
        return ERROR_EXPR_EXPECTED_NUM;
    switch (op) {
    case TOKEN_MINUS:
        if (executeMode) stackPushNum(stackPopNum() * -1.0f);
        return TYPE_NUMBER;
    case TOKEN_NOT:
        if (executeMode) stackPushNum(stackPopNum() ? 0.0f : 1.0f);
        return TYPE_NUMBER;
    default:
        return ERROR_UNEXPECTED_TOKEN;
    }
}

/// primary
int parsePrimary() {
    switch (curToken) {
    case TOKEN_IDENT:	
        return parseIdentifierExpr();
    case TOKEN_NUMBER:
    case TOKEN_INTEGER:
        return parseNumberExpr();
    case TOKEN_STRING:	
        return parseStringExpr();
    case TOKEN_LBRACKET:
        return parseParenExpr();

        // "psuedo-identifiers"
    case TOKEN_RND:
    case TOKEN_PI:
        return parse_PseudoID();
    case TOKEN_INKEY:
        return parse_INKEY();

        // unary ops
    case TOKEN_MINUS:
    case TOKEN_NOT:
        return parseUnaryNumExp();

        // functions
    case TOKEN_INT: 
    case TOKEN_ABS:
    case TOKEN_STR: 
    case TOKEN_CHR:
    case TOKEN_LEN: 
    case TOKEN_CODE:
    case TOKEN_VAL:
    case TOKEN_LEFT: 
    case TOKEN_RIGHT: 
    case TOKEN_MID: 
    case TOKEN_PINREAD:
    case TOKEN_ANALOGRD:
    case TOKEN_POW:
    case TOKEN_INPB:
    case TOKEN_INPW:
    case TOKEN_HEX:
    case TOKEN_PEEK:
        return parseFnCallExpr();

        // single argument math functions
    case TOKEN_COS:
    case TOKEN_SIN:
    case TOKEN_TAN:
    case TOKEN_ACS:
    case TOKEN_ASN:
    case TOKEN_ATN:
    case TOKEN_EXP:
    case TOKEN_LN:
        return parseMathFn();

    default:
        return ERROR_UNEXPECTED_TOKEN;
    }
}

int getTokPrecedence() {
    if (curToken == TOKEN_AND || curToken == TOKEN_OR) return 5;
    if (curToken == TOKEN_EQUALS || curToken == TOKEN_NOT_EQ) return 10;
    if (curToken == TOKEN_LT || curToken == TOKEN_GT || curToken == TOKEN_LT_EQ || curToken == TOKEN_GT_EQ) return 20;
    if (curToken == TOKEN_MINUS || curToken == TOKEN_PLUS) return 30;
    else if (curToken == TOKEN_MULT || curToken == TOKEN_DIV || curToken == TOKEN_MOD) return 40;
    else return -1;
}

// Operator-Precedence Parsing
int parseBinOpRHS(int ExprPrec, int lhsVal) {
    // If this is a binop, find its precedence.
    while (1) {
        int TokPrec = getTokPrecedence();

        // If this is a binop that binds at least as tightly as the current binop,
        // consume it, otherwise we are done.
        if (TokPrec < ExprPrec)
            return lhsVal;

        // Okay, we know this is a binop.
        int BinOp = curToken;
        getNextToken();  // eat binop

        // Parse the primary expression after the binary operator.
        int rhsVal = parsePrimary();
        if (rhsVal & ERROR_MASK) return rhsVal;

        // If BinOp binds less tightly with RHS than the operator after RHS, let
        // the pending operator take RHS as its LHS.
        int NextPrec = getTokPrecedence();
        if (TokPrec < NextPrec) {
            rhsVal = parseBinOpRHS(TokPrec+1, rhsVal);
            if (rhsVal & ERROR_MASK) return rhsVal;
        }

        if (IS_TYPE_NUM(lhsVal) && IS_TYPE_NUM(rhsVal))
        {	// Number operations
            float r, l;
            if (executeMode) {
                r = stackPopNum();
                l = stackPopNum();
            }
            if (BinOp == TOKEN_PLUS) {
                if (executeMode) stackPushNum(l+r);
            }
            else if (BinOp == TOKEN_MINUS) {
                if (executeMode) stackPushNum(l-r);
            }
            else if (BinOp == TOKEN_MULT) {
                if (executeMode) stackPushNum(l*r);
            }
            else if (BinOp == TOKEN_DIV) {
                if (executeMode) {
                    if (r) stackPushNum(l/r);
                    else return ERROR_EXPR_DIV_ZERO;
                }
            }
            else if (BinOp == TOKEN_MOD) {
                if (executeMode) {
                    if ((int)r) stackPushNum((float)((int)l % (int)r));
                    else return ERROR_EXPR_DIV_ZERO;
                }
            }
            else if (BinOp == TOKEN_LT) {
                if (executeMode) stackPushNum(l < r ? 1.0f : 0.0f);
            }
            else if (BinOp == TOKEN_GT) {
                if (executeMode) stackPushNum(l > r ? 1.0f : 0.0f);
            }
            else if (BinOp == TOKEN_EQUALS) {
                if (executeMode) stackPushNum(l == r ? 1.0f : 0.0f);
            }
            else if (BinOp == TOKEN_NOT_EQ) {
                if (executeMode) stackPushNum(l != r ? 1.0f : 0.0f);
            }
            else if (BinOp == TOKEN_LT_EQ) {
                if (executeMode) stackPushNum(l <= r ? 1.0f : 0.0f);
            }
            else if (BinOp == TOKEN_GT_EQ) {
                if (executeMode) stackPushNum(l >= r ? 1.0f : 0.0f);
            }
            else if (BinOp == TOKEN_AND) {
                if (executeMode) stackPushNum(r != 0.0f ? l : 0.0f);
            }
            else if (BinOp == TOKEN_OR) {
                if (executeMode) stackPushNum(r != 0.0f ? 1 : l);
            }
            else
                return ERROR_UNEXPECTED_TOKEN;
        }
        else if (IS_TYPE_STR(lhsVal) && IS_TYPE_STR(rhsVal))
        {	// String operations
            if (BinOp == TOKEN_PLUS) {
                if (executeMode)
                    stackAdd2Strs();
            }
            else if (BinOp >= TOKEN_EQUALS && BinOp <=TOKEN_LT_EQ) {
                if (executeMode) {
                    char *r = stackPopStr();
                    char *l = stackPopStr();
                    int ret = strcmp(l,r);
                    if (BinOp == TOKEN_EQUALS && ret == 0) stackPushNum(1.0f);
                    else if (BinOp == TOKEN_NOT_EQ && ret != 0) stackPushNum(1.0f);
                    else if (BinOp == TOKEN_GT && ret > 0) stackPushNum(1.0f);
                    else if (BinOp == TOKEN_LT && ret < 0) stackPushNum(1.0f);
                    else if (BinOp == TOKEN_GT_EQ && ret >= 0) stackPushNum(1.0f);
                    else if (BinOp == TOKEN_LT_EQ && ret <= 0) stackPushNum(1.0f);
                    else stackPushNum(0.0f);
                }
                lhsVal = TYPE_NUMBER;
            }
            else
                return ERROR_UNEXPECTED_TOKEN;
        }
        else
            return ERROR_UNEXPECTED_TOKEN;
    }
}

int parseExpression()
{
    int val = parsePrimary();
    if (val & ERROR_MASK) return val;
    return parseBinOpRHS(0, val);
}

int expectNumber() {
    int val = parseExpression();
    if (val & ERROR_MASK) return val;
    if (!IS_TYPE_NUM(val))
        return ERROR_EXPR_EXPECTED_NUM;
    return 0;
}

// parse both RUN and RESTORE
int parse_RUN(int isRestore) {
    getNextToken();
    uint16_t startLine = 1;
    if (curToken != TOKEN_EOL) {
        int val = expectNumber();
        if (val) return val;	// error
        if (executeMode) {
            startLine = (uint16_t)stackPopNum();
            /*if (startLine <= 0)
                return ERROR_BAD_LINE_NUM;*/
        }
    }
    if (executeMode) {
        if (isRestore) {
            dataLineNumber = startLine;
        }
        else {
            // clear variables
            sysVARSTART = sysVAREND = sysGOSUBSTART = sysGOSUBEND = MEMORY_SIZE;
            jumpLineNumber = startLine;
            stopLineNumber = stopStmtNumber = 0;
            dataLineNumber = 1;
        }
    }
    return 0;
}

int parse_GOTO() {
    getNextToken();
    int val = expectNumber();
    if (val) return val;	// error
    if (executeMode) {
        uint16_t startLine = (uint16_t)stackPopNum();
        /*if (startLine <= 0)
            return ERROR_BAD_LINE_NUM;*/
        jumpLineNumber = startLine;
    }
    return 0;
}

int parse_PAUSE() {
    getNextToken();
    int val = expectNumber();
    if (val) return val;	// error
    if (executeMode) {
        long ms = (long)stackPopNum();
        if (ms < 0)
            return ERROR_BAD_PARAMETER;
        host_sleep(ms);
    }
    return 0;
}

int parse_MODE() {
    getNextToken();
    int val = expectNumber();
    if (val) return val;	// error
    if (executeMode) {
        int mode = (int)stackPopNum();
        host_mode(mode);
    }
    return 0;
}

int parse_LIST() {
    getNextToken();
    uint16_t first = 0, last = 0;
    if (curToken != TOKEN_EOL && curToken != TOKEN_CMD_SEP) {
        int val = expectNumber();
        if (val) return val;	// error
        if (executeMode)
            first = (uint16_t)stackPopNum();
    }
    if (curToken == TOKEN_COMMA) {
        getNextToken();
        int val = expectNumber();
        if (val) return val;	// error
        if (executeMode)
            last = (uint16_t)stackPopNum();
    }
    if (executeMode) {
        listProg(first,last);
        host_showBuffer();
    }
    return 0;
}

int parse_PRINT() {
    getNextToken();
    // zero + expressions seperated by semicolons or commas
    int newLine = 1;
    while (curToken != TOKEN_EOL && curToken != TOKEN_CMD_SEP) {
        int val = parseExpression();
        if (val & ERROR_MASK) return val;
        if (executeMode) {
            if (IS_TYPE_NUM(val))
                host_outputFloat(stackPopNum());
            else
                host_outputString(stackPopStr());
            newLine = 1;
        }
        if (curToken == TOKEN_SEMICOLON) {
            newLine = 0;
            getNextToken();
        }
        if (curToken == TOKEN_COMMA) {
            newLine = 0;
            getNextToken();
            if (executeMode) host_outputString("\t");
        }
    }
    if (executeMode) {
        if (newLine)
            host_newLine();
        host_showBuffer();
    }
    return 0;
}

// parse a stmt that takes N int parameters (max 3)
// e.g. POSITION 3,2
int parseNIntCmd(int n) {
    int i;
    int op = curToken;
    int para[3];
    if (n > 3) return ERROR_LEXER_TOO_LONG;
    getNextToken();
    int val = expectNumber();
    if (val) return val;	// error
    for (i=1; i<n; i++) {
        if (curToken != TOKEN_COMMA)
            return ERROR_UNEXPECTED_TOKEN;
        getNextToken();
        val = expectNumber();
        if (val) return val;	// error
    }
    if (executeMode) {
        for (i=n-1; i>=0; i--)
            para[i] = (int)stackPopNum();
        switch(op) {
        case TOKEN_POSITION: 
            host_moveCursor(para[0],para[1]);
            break;
        case TOKEN_PIN: 
            host_digitalWrite(para[0],para[1]);
            break;
        case TOKEN_PINMODE: 
            host_pinMode(para[0],para[1]);
            break;
        case TOKEN_COLOR:
            host_color(para[0],para[1]);
            break;
        case TOKEN_PLOT:
            host_plot(para[0],para[1]);
            break;
        case TOKEN_DRAW:
            host_draw(para[0],para[1]);
            break;
        case TOKEN_CIRCLE:
            host_circle(para[0],para[1],para[2]);
            break;
        case TOKEN_OUTB:
            host_outb(para[0],para[1]);
            break;
        case TOKEN_OUTW:
            host_outw(para[0],para[1]);
            break;
        case TOKEN_POKE:
            host_pokeb(para[0],para[1],para[2]);
            break;
        }
    }
    return 0;
}

// get number or string from DATA statement
int readDataStmt() {
    int token, ret;
    int type = TYPE_NUMBER;
    static unsigned char *p;
    if (dataLineNumber) {
        p = findProgLine(dataLineNumber);
nextdata:
        for (;;) {
            if (p == &mem[sysPROGEND])
                    return ERROR_NO_DATA_FOR_READ;;
            if (*(p + 2 + sizeof(uint16_t)) != TOKEN_DATA) {
                p+= *(uint16_t *)p;         // next line
                continue;
            }
            p+= 2 + sizeof(uint16_t) + 1;   // line size + line number + DATA token
            dataLineNumber = 0;
            break;
        }
    }
    token = *p++;
    switch (token) {
    case TOKEN_NUMBER:
        ret = stackPushNum(*(float *)p);
        p += sizeof(float);
        break;
    case TOKEN_INTEGER:
        ret = stackPushNum(*(long *)p);
        p += sizeof(long);
        break;
    case TOKEN_STRING:
        ret = stackPushStr((char *)p);
        p += strlen((char *)p) + 1;
        type = TYPE_STRING;
        break;
    case TOKEN_EOL:
        goto nextdata;
    }
    if (*p != TOKEN_EOL) p+= 1;  // skip COMMA
    if (!ret) return ERROR_OUT_OF_MEMORY;
    return type;
}

// this handles LET a$="hello", INPUT a$ and READ a$ type assignments
int parseAssignment(int token) {
    char ident[MAX_IDENT_LEN+1];
    int val;
    if (token == TOKEN_INPUT && curToken == TOKEN_STRING) {
        int val = parseExpression();
        if (val & ERROR_MASK) return val;
        if (curToken != TOKEN_COMMA) return ERROR_UNEXPECTED_TOKEN;
        if (executeMode)
            host_outputString(stackPopStr());
        getNextToken();
    }
    if (curToken != TOKEN_IDENT) return ERROR_UNEXPECTED_TOKEN;
    if (executeMode)
        strcpy(ident, identVal);
    int isStringIdentifier = isStrIdent;
    int isArray = 0;
    getNextToken();	// eat ident
    if (curToken == TOKEN_LBRACKET) {
        // array element being set
        val = parseSubscriptExpr();
        if (val) return val;
        isArray = 1;
    }
    if (token == TOKEN_INPUT) {
        // from INPUT statement
        if (executeMode) {
            char *inputStr = host_readLine();
            if (!inputStr) return ERROR_BREAK_PRESSED;
            if (isStringIdentifier) {
                if (!stackPushStr(inputStr)) return ERROR_OUT_OF_MEMORY;
            }
            else {
                float f = (float)strtod(inputStr, 0);
                if (!stackPushNum(f)) return ERROR_OUT_OF_MEMORY;
            }
            host_newLine();
            host_showBuffer();
        }
        val = isStringIdentifier ? TYPE_STRING : TYPE_NUMBER;
    } else if (token == TOKEN_READ) {
        val = isStringIdentifier ? TYPE_STRING : TYPE_NUMBER;
        if (executeMode) {
            val = readDataStmt();
            if (val & ERROR_MASK) return val;
        }
    }
    else {
        // from LET statement
        if (curToken != TOKEN_EQUALS) return ERROR_UNEXPECTED_TOKEN;
        getNextToken(); // eat =
        val = parseExpression();
        if (val & ERROR_MASK) return val;
    }
    // type checking and actual assignment
    if (!isStringIdentifier)
    {	// numeric variable
        if (!IS_TYPE_NUM(val)) return ERROR_EXPR_EXPECTED_NUM;
        if (executeMode) {
            if (isArray) {
                val = setNumArrayElem(ident, stackPopNum());
                if (val) return val;
            }
            else {
                if (!storeNumVariable(ident, stackPopNum())) return ERROR_OUT_OF_MEMORY;
            }
        }
    }
    else
    {	// string variable
        if (!IS_TYPE_STR(val)) return ERROR_EXPR_EXPECTED_STR;
        if (executeMode) {
            if (isArray) {
                // annoyingly, we've got the string at the top of the stack
                // (from parseExpression) and the array index stuff (from
                // parseSubscriptExpr) underneath.
                val = setStrArrayElem(ident);
                if (val) return val;
            }
            else {
                if (!storeStrVariable(ident, stackGetStr())) return ERROR_OUT_OF_MEMORY;
                stackPopStr();
            }
        }
    }
    return 0;
}

int parse_IF() {
    getNextToken();	// eat if
    int val = expectNumber();
    if (val) return val;	// error
    if (curToken != TOKEN_THEN)
        return ERROR_MISSING_THEN;
    getNextToken();
    if (executeMode && stackPopNum() == 0.0f) {
        // condition not met
        breakCurrentLine = 1;
        return 0;
    }
    else return 0;
}

int parse_FOR() {
    char ident[MAX_IDENT_LEN+1];
    float start, end, step = 1.0f;
    getNextToken();	// eat for
    if (curToken != TOKEN_IDENT || isStrIdent) return ERROR_UNEXPECTED_TOKEN;
    if (executeMode)
        strcpy(ident, identVal);
    getNextToken();	// eat ident
    if (curToken != TOKEN_EQUALS) return ERROR_UNEXPECTED_TOKEN;
    getNextToken(); // eat =
    // parse START
    int val = expectNumber();
    if (val) return val;	// error
    if (executeMode)
        start = stackPopNum();
    // parse TO
    if (curToken != TOKEN_TO) return ERROR_UNEXPECTED_TOKEN;
    getNextToken(); // eat TO
    // parse END
    val = expectNumber();
    if (val) return val;	// error
    if (executeMode)
        end = stackPopNum();
    // parse optional STEP
    if (curToken == TOKEN_STEP) {
        getNextToken(); // eat STEP
        val = expectNumber();
        if (val) return val;	// error
        if (executeMode)
            step = stackPopNum();
    }
    if (executeMode) {
        if (!storeForNextVariable(ident, start, step, end, lineNumber, stmtNumber)) return ERROR_OUT_OF_MEMORY;
    }
    return 0;
}

int parse_NEXT() {
    getNextToken();	// eat next
    if (curToken != TOKEN_IDENT || isStrIdent) return ERROR_UNEXPECTED_TOKEN;
    if (executeMode) {
        ForNextData data = lookupForNextVariable(identVal);
        if (data.val == FLT_MAX) return ERROR_VARIABLE_NOT_FOUND;
        else if (data.step == FLT_MAX) return ERROR_NEXT_WITHOUT_FOR;
        // update and store the count variable
        data.val += data.step;
        storeNumVariable(identVal, data.val);
        // loop?
        if ((data.step >= 0 && data.val <= data.end) || (data.step < 0 && data.val >= data.end)) {
            jumpLineNumber = data.lineNumber;
            jumpStmtNumber = data.stmtNumber+1;
        }
    }
    getNextToken();	// eat ident
    return 0;
}

int parse_GOSUB() {
    getNextToken();	// eat gosub
    int val = expectNumber();
    if (val) return val;	// error
    if (executeMode) {
        uint16_t startLine = (uint16_t)stackPopNum();
        /*if (startLine <= 0)
            return ERROR_BAD_LINE_NUM;*/
        jumpLineNumber = startLine;
        if (!gosubStackPush(lineNumber,stmtNumber))
            return ERROR_OUT_OF_MEMORY;
    }
    return 0;
}

// LOAD or LOAD "x"
// SAVE, SAVE+ or SAVE "x"
// DELETE "x"
int parseLoadSaveCmd() {
    int op = curToken;
    int autoexec = 0, gotFileName = 0;
    getNextToken();
    if (op == TOKEN_SAVE && curToken == TOKEN_PLUS) {
        getNextToken();
        autoexec = 1;
    }
    if (curToken != TOKEN_EOL && curToken != TOKEN_CMD_SEP) {
        int val = parseExpression();
        if (val & ERROR_MASK) return val;
        if (!IS_TYPE_STR(val))
            return ERROR_EXPR_EXPECTED_STR;
        gotFileName = 1;
    }

    if (executeMode) {
        if (gotFileName) {
            char fileName[MAX_PATH_LEN];
            if (strlen(stackGetStr()) > MAX_PATH_LEN-1)
                return ERROR_BAD_PARAMETER;
            strcpy(fileName, stackPopStr());
#if DISK_FUNCTIONS
            if (op == TOKEN_SAVE)
                return host_saveProgramToFile(fileName, autoexec);
            else if (op == TOKEN_LOAD) {
                reset();
                return host_loadProgramFromFile(fileName);
            }
            else if (op == TOKEN_DELETE)
                return host_removeFile(fileName);
#endif
        } else return ERROR_EXPR_EXPECTED_STR;
        return ERROR_UNEXPECTED_CMD;
    }
    return 0;
}

int parseSimpleCmd() {
    int op = curToken;
    getNextToken();	// eat op
    if (executeMode) {
        switch (op) {
            case TOKEN_NEW:
                reset();
                breakCurrentLine = 1;
                break;
            case TOKEN_STOP:
                stopLineNumber = lineNumber;
                stopStmtNumber = stmtNumber;
                return ERROR_STOP_STATEMENT;
            case TOKEN_CONT:
                if (stopLineNumber) {
                    jumpLineNumber = stopLineNumber;
                    jumpStmtNumber = stopStmtNumber+1;
                }
                break;
            case TOKEN_RETURN:
            {
                int returnLineNumber, returnStmtNumber;
                if (!gosubStackPop(&returnLineNumber, &returnStmtNumber))
                    return ERROR_RETURN_WITHOUT_GOSUB;
                jumpLineNumber = returnLineNumber;
                jumpStmtNumber = returnStmtNumber+1;
                break;
            }
            case TOKEN_CLS:
                host_cls();
                host_showBuffer();
                break;
            case TOKEN_DIR:
#if DISK_FUNCTIONS
                return host_directoryListing();
#else
                return ERROR_FILE_ERROR;
#endif
                break;
        }
    }
    return 0;
}

int parse_DIM() {
    char ident[MAX_IDENT_LEN+1];
    getNextToken();	// eat DIM
    if (curToken != TOKEN_IDENT) return ERROR_UNEXPECTED_TOKEN;
    if (executeMode)
        strcpy(ident, identVal);
    int isStringIdentifier = isStrIdent;
    getNextToken();	// eat ident
    int val = parseSubscriptExpr();
    if (val) return val;
    if (executeMode && !createArray(ident, isStringIdentifier ? 1 : 0))
        return ERROR_OUT_OF_MEMORY;
    return 0;
}

int parse_DATA() {
    getNextToken();	// eat DATA
    for (;;) {
        switch (curToken) {
        case TOKEN_NUMBER:
        case TOKEN_INTEGER:
        case TOKEN_STRING:
            getNextToken();
            break;
        default:
            return ERROR_UNEXPECTED_TOKEN;
        }
        if (curToken == TOKEN_EOL)
            break;
        if (curToken != TOKEN_COMMA)
            return ERROR_UNEXPECTED_TOKEN;
        getNextToken();
    }
    return 0;
}

static int targetStmtNumber;
int parseStmts()
{
    int ret = 0, lastToken;
    breakCurrentLine = 0;
    jumpLineNumber = 0;
    jumpStmtNumber = 0;

    while (ret == 0) {
        if (curToken == TOKEN_EOL)
            break;
        if (executeMode)
            sysSTACKEND = sysSTACKSTART = sysPROGEND;	// clear calculator stack
        int needCmdSep = 1;
        switch (curToken) {
        case TOKEN_PRINT: ret = parse_PRINT(); break;
        case TOKEN_IDENT: ret = parseAssignment(TOKEN_IDENT); break;
        case TOKEN_LIST: ret = parse_LIST(); break;
        case TOKEN_RUN: ret = parse_RUN(false); break;
        case TOKEN_RESTORE: ret = parse_RUN(true); break;
        case TOKEN_GOTO: ret = parse_GOTO(); break;
        case TOKEN_REM: getNextToken(); getNextToken(); break;
        case TOKEN_IF: ret = parse_IF(); needCmdSep = 0; break;
        case TOKEN_FOR: ret = parse_FOR(); break;
        case TOKEN_NEXT: ret = parse_NEXT(); break;
        case TOKEN_GOSUB: ret = parse_GOSUB(); break;
        case TOKEN_DIM: ret = parse_DIM(); break;
        case TOKEN_PAUSE: ret = parse_PAUSE(); break;
        case TOKEN_MODE: ret = parse_MODE(); break;
        case TOKEN_DATA: ret = parse_DATA(); break;
        
        case TOKEN_LET:
        case TOKEN_INPUT:
        case TOKEN_READ:
        case TOKEN_INPB:
        case TOKEN_INPW:
            lastToken = curToken;
            getNextToken();
            ret = parseAssignment(lastToken);
            break;

        case TOKEN_LOAD:
        case TOKEN_SAVE:
        case TOKEN_DELETE:
            ret = parseLoadSaveCmd();
            break;
        
        case TOKEN_POSITION:
        case TOKEN_PIN:
        case TOKEN_PINMODE:
        case TOKEN_COLOR:
        case TOKEN_PLOT:
        case TOKEN_DRAW:
        case TOKEN_OUTB:
        case TOKEN_OUTW:
            ret = parseNIntCmd(2);
            break;

        case TOKEN_CIRCLE:
        case TOKEN_POKE:
            ret = parseNIntCmd(3);
            break;

        case TOKEN_NEW:
        case TOKEN_STOP:
        case TOKEN_CONT:
        case TOKEN_RETURN:
        case TOKEN_CLS:
        case TOKEN_DIR:
            ret = parseSimpleCmd();
            break;
            
        default: 
            ret = ERROR_UNEXPECTED_CMD;
        }
        // if error, or the execution line has been changed, exit here
        if (ret || breakCurrentLine || jumpLineNumber || jumpStmtNumber)
            break;
        // it should either be the end of the line now, and (generally) a command seperator
        // before the next command
        if (curToken != TOKEN_EOL) {
            if (needCmdSep) {
                if (curToken != TOKEN_CMD_SEP) ret = ERROR_UNEXPECTED_CMD;
                else {
                    getNextToken();
                    // don't allow a trailing :
                    if (curToken == TOKEN_EOL) ret = ERROR_UNEXPECTED_CMD;
                }
            }
        }
        // increase the statement number
        stmtNumber++;
        // if we're just scanning to find a target statement, check
        if (stmtNumber == targetStmtNumber)
            break;
    }
    return ret;
}

int processInput(unsigned char *tokenBuf) {
    // first token can be TOKEN_INTEGER for line number - stored as a float in numVal
    // store as WORD line number (max 65535)
    tokenBuffer = tokenBuf;
    getNextToken();
    // check for a line number at the start
    uint16_t gotLineNumber = 0;
    unsigned char *lineStartPtr = 0;
    if (curToken == TOKEN_INTEGER) {
        long val = (long)numVal;
        if (val > 65535)
            return ERROR_LINE_NUM_TOO_BIG;
        if (val == 0)
                return ERROR_LEXER_BAD_NUM;
        else {
            gotLineNumber = (uint16_t)val;
            lineStartPtr = tokenBuffer;
            getNextToken();
        }
    }

    executeMode = 0;
    targetStmtNumber = 0;
    int ret = parseStmts();	// syntax check
    if (ret != ERROR_NONE)
        return ret;

    if (gotLineNumber) {
        if (!doProgLine(gotLineNumber, lineStartPtr, tokenBuffer - lineStartPtr))
            ret = ERROR_OUT_OF_MEMORY;
    }
    else {
        // we start off executing from the input buffer
        tokenBuffer = tokenBuf;
        executeMode = 1;
        lineNumber = 0;	// buffer
        unsigned char *p;

        while (1) {
            getNextToken();

            stmtNumber = 0;
            // skip any statements? (e.g. for/next)
            if (targetStmtNumber) {
                executeMode = 0; 
                parseStmts(); 
                executeMode = 1;
                targetStmtNumber = 0;
            }
            // now execute
            ret = parseStmts();
            if (ret != ERROR_NONE)
                break;

            // are we processing the input buffer?
            if (!lineNumber && !jumpLineNumber && !jumpStmtNumber)
                break;	// if no control flow jumps, then just exit

            // are we RETURNing to the input buffer?
            if (lineNumber && !jumpLineNumber && jumpStmtNumber)
                lineNumber = 0;

            if (!lineNumber && !jumpLineNumber && jumpStmtNumber) {
                // we're executing the buffer, and need to jump stmt (e.g. for/next)
                tokenBuffer = tokenBuf;
            }
            else {
                // we're executing the program
                if (jumpLineNumber || jumpStmtNumber) {
                    // line/statement number was changed e.g. goto
                    p = findProgLine(jumpLineNumber);
                }
                else {
                    // line number didn't change, so just move one to the next one
                    p+= *(uint16_t *)p;
                }
                // end of program?
                if (p == &mem[sysPROGEND])
                    break;	// end of program

                lineNumber = *(uint16_t*)(p+2);
                tokenBuffer = p+4;
                // if the target for a jump is missing (e.g. line deleted) and we're on the next line
                // reset the stmt number to 0
                if (jumpLineNumber && jumpStmtNumber && lineNumber > jumpLineNumber)
                    jumpStmtNumber = 0;
            }
            if (jumpStmtNumber)
                targetStmtNumber = jumpStmtNumber;

            if (host_breakPressed())
            { 
                ret = ERROR_BREAK_PRESSED; 
                break; 
            }
        }
    }
    return ret;
}

void reset() {
    // program at the start of memory
    sysPROGEND = 0;
    // stack is at the end of the program area
    sysSTACKSTART = sysSTACKEND = sysPROGEND;
    // variables/gosub stack at the end of memory
    sysVARSTART = sysVAREND = sysGOSUBSTART = sysGOSUBEND = MEMORY_SIZE;
    memset(&mem[0], 0, MEMORY_SIZE);

    stopLineNumber = 0;
    stopStmtNumber = 0;
    lineNumber = 0;
}
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