MQL4 multi-timeframe indicator - trading

I would like to write out an indicator that can take in input the int shift of an assigned timeframe, and turns out a value related to another timeframe.
As an example, I would like to write an MACD indicator over a 100 periods of M15, that can return out its value 1,2,3,4,5,6,7... minutes before the current candle.
Since in the current candle this indicator "changes" its value, tick by tick, I think that should be possible to write out such an indicator, but I can not figure out how to do it.

MQL4 language principally has tools for this:
However, as noted above, your experimentation will need thorough quant validations, as the earlier Builds did not support this in [MT4-Strategy Tester] code-execution environment ( and more recent shifts into New-MQL4.56789 have devastated performance constraints for all [CustomIndicators], the all [MT4-graph]-GUI-s together plus the all [Expert Advisor]-s use, since all these suddenly share one ( yes, ONE and THE ONLY ) computing thread.
Ok, you have been warned :o)
So,
if indeed keen to equip your [CustomIndicator] so as to be independent of the GUI-native-TimeFrame, all your calculations inside such [CustomIndicator]-code must use indirect access-tools to source the PriceDOMAIN data - so never use any { Open[] | High[] | Low[] | Close[] }-TimeSeries data directly, but only using { iOpen() | iHigh() | iLow() | iClose() }
All these access tools conceptually have a common signature:
double iLow( string symbol, // symbol
int timeframe, // timeframe
int shift // shift
);
and
if your code
obeys this duty,
your [CustomIndicator]( iff the StrategyTester will not finally spoil the game -- due quant testing will show this )
will be working with data from timeframe & shift of your wish.
Implementation remarks:
Your [CustomIndicator]-code has to implement a "non-GUI-shift" independently from the GUI-native-TimeFrame shift-counting. See an iCustom() signature template for inspiration. The GUI-TimeFrame-shift is like moving the line-graph on GUI-screen, i.e. in GUI-native-TimeFrame steps, not taking into account your [CustomIndicator] "internal"-"non-GUI-shift" values, so your code has to be smarter, so as to process this "internal"-"non-GUI-shift" during a value generation. If in doubts, during prototyping, validate the proper "mechanics" on Time[aShiftINTENDED] vs iTime( _Symbol, PERIOD_INTENDED, aShiftINTENDED )
Due to quite a lot of points, where an iCustom() call-interface may be a bit misleading, or a revision-change-management error-prone, we got used to use a formal template for each [Custom Indicator] code, helping to maintain referential integrity with a iCustom() use in the actual [ExpertAdvisor] code. It might seem a bit dumb, but those, who have spent man*hours in search for a bug in { un- | ill- }-propagated call-interface changes, this may become a life-saver.
We formalise the call-interface in such a way, that this section, maintained in the [CustomIndicator]-code, can always be copied into the [ExpertAdviser] code, so that the iCustom() signature-match can be inspected.
//vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
//!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
//!!!!
//---- indicator parameters -------------------------------------------------
// POSITIONAL ORDINAL-NUMBERED CALLING INTERFACE
// all iCustom() calls MUST BE REVISED ON REVISION
//!!!!
//!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
#define XEMA_CUSTOM_INDICATOR_NAME "EMA_DEMA_TEMA_XEMA_wShift" // this.
//--- input parameters ------------------------------------------------------ iCustom( ) CALL INTERFACE
input int nBARs_period = 8;
extern double MUL_SIGMA = 2.5;
sinput ENUM_APPLIED_PRICE aPriceTYPE = PRICE_CLOSE;
extern int ShiftBARs = 0;
//!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
//!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
//!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
/* = iCustom( _Symbol,
PERIOD_CURRENT, XEMA_CUSTOM_INDICATOR_NAME, // |-> iCustom INDICATOR NAME
XEMA_nBARs_period, // |-> input nBARs_period
XEMA_MUL_SIGMA, // |-> input MUL_SIGMA
XEMA_PRICE_TYPE, // |-> input aPriceTYPE from: ENUM_APPLIED_PRICE
XEMA_ShiftBARs, // |-> input ShiftBARs
XEMA_<_VALUE_>_BUFFER_ID, // |-> line# --------------------------------------------from: { #define'd (e)nums ... }
0 // |-> [0]-aTimeDOMAIN-offset
); //
*/
#define XEMA_Main_AXIS_BUFFER_ID 0 // <----xEMA<maxEMAtoCOMPUTE>[]
#define XEMA_UpperBAND_BUFFER_ID 1
#define XEMA_LowerBAND_BUFFER_ID 2
#define XEMA_StdDEV____BUFFER_ID 3
#define XEMA_SimpleEMA_BUFFER_ID 4 // sEMA
#define XEMA_DoubleEMA_BUFFER_ID 10 // dEMA
#define XEMA_TripleEMA_BUFFER_ID 11 // tEMA
//!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
//!!!!
//---- indicator parameters -------------------------------------------------
// POSITIONAL ORDINAL-NUMBERED CALLING INTERFACE
// all iCustom() calls MUST BE REVISED ON REVISION
//!!!!
//!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
//^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Found a way to write it in a very simple way:
double M1 (int shift) {double val = iCustom(NULL,PERIOD_M1, "my_indicator",100,2.0,30.0,0,shift); return(val);}
double M15 (int shift) {double val = iCustom(NULL,PERIOD_M15,"my_indicator",100,2.0,30.0,0,shift); return(val);}
int s1_15;
double B_M1_M15(int i) {
if (i>=0 && i<15 ) s1_15=0;
else if (i>=15 && i<30 ) s1_15=1;
else if (i>=30 && i<45 ) s1_15=2;
else if (i>=45 && i<60 ) s1_15=3;
else if (i>=60 && i<75 ) s1_15=4;
return NormalizeDouble(MathAbs(M1(i) - M15(s1_15)),Digits);
}
and so on for every others couples of timeframe.

Related

About extending a Look Up Table at compile time

I'd like to extend my instrumental Profiler in order to avoid it affect too much performances.
Im my current implementation, I'm using a ProfilerHelper taking one string, which is put whereever you want in the profiling f().
The ctor is starting the measurement and the dector is closing it, logging the Delta in an unordered_map entry, which is key is the string.
Now, I'd like to turn all of that into a faster stuff.
First of all, I'd like to create a string LUT (Look Up Table) contaning the f()s names at compile time, and turn the unordered_map to a plain vector which is paired by the string function LUT.
Now the question is: I've managed to create a LUT but std::string_view, but I cannot find a way to extend it at compile time.
A first rought trial sounds like this:
template<unsigned N>
constexpr auto LUT() {
std::array<std::string_view, N> Strs{};
for (unsigned n = 0; n < N; n++) {
Strs[n] = "";
}
return Strs;
};
constexpr std::array<std::string_view, 0> StringsLUT { LUT<0>() };
constexpr auto AddString(std::string_view const& Str)
{
constexpr auto Size = StringsLUT.size();
std::array<std::string_view, Size + 1> Copy{};
for (auto i = 0; i < Size; ++i)
Copy[i] = StringsLUT[i];
Copy[Size] = Str;
return Copy;
};
int main()
{
constexpr auto Strs = AddString(__builtin_FUNCTION());
//for (auto const Str : Strs)
std::cout << Strs[0] << std::endl;
}
So my idea should be to recall the AddString whenever needed in my f()s to be profiled, extending this list at compile time.
But of course I should take the returned Copy and replace the StringsLUT everytime, to land to a final StringsLUT with all the f() names inside it.
Is there a way to do that at compile time?
Sorry, but I'm just entering the magic "new" world of constexpr applied to LUT right in these days.
Tx for your support in advance.

Comment not being used in trade MQL4

Unfortunately I am not able to post the code I am debugging as it is not mine and I am bound not to show it... BUT I will describe it as detailed as possible.
There are 4 strategies base on 4 indicators, custom, and not-custom ones. So basically instead of 4 different EAs running in 4 different charts with the same 4 indicators each... The client asked me to optimise them by putting them all in one to run 4 into 1 EAs in the same chart.
EVERYTHING is the same. They are tested as well that they are the same. They open the same trades, on the same moments. Nothing is changed 100%. The only thing I did (for this part of the debugging, because obviously I had a lot more to do before that) is to copy functions and code. And I seperated all different strategies with an "if" as input
input bool strategy1enabled = true; etc... so he/she can disable/enable individual strategies if wanted.
everything works BUT....
All but 1 strategies, does not show the Comment on the trades.
All 4 use the same Buy/Sell/CloseOrder functions so I just input the values to keep the code shorter.
//---
bool OrdClose (int ticket_number, double lt, int slp)
{
return OrderClose(ticket_number,lt,iClose(NULL,0,0),slp,clrViolet);
}
//---
int Buy(double lt, int slp, int slss, int tpft, string cmt, int mgc)
{
return OrderSend(NULL,OP_BUY,lt,Ask,slp,Ask-slss*Point,Ask+tpft*Point,cmt,mgc,0,clrDarkBlue);
}
//---
int Sell(double lt, int slp, int slss, int tpft, string cmt, int mgc)
{
return OrderSend(NULL,OP_SELL,lt,Bid,slp,Bid+slss*Point,Bid-tpft*Point,cmt,mgc,0,clrDarkRed);
}
1 strategy just refuses to put comment. Any ideas why? When used seperated WITH THE SAME CODE and the EXACT SAME functions... comment shows...
EDIT:
2021.05.04 18:30:48.670 The_Big_Holla_v1_8_EA CADJPY,H1: open #85710545 buy 0.06 CADJPY at 88.755 sl: 88.655 tp: 88.955 ok
2021.05.04 18:30:48.462 The_Big_Holla_v1_8_EA CADJPY,H1: Holla v4.9 || GreedInjectionMode
2021.05.04 18:30:48.462 The_Big_Holla_v1_8_EA CADJPY,H1: Holla v4.9 || GreedInjectionMode
Comment is passed properly and checked before being passed to function and before OrderSend within function:
The function:
int Sell(double lt, int slp, int slss, int tpft, string cmt, int mgc)
{
Print(cmt);
return OrderSend(NULL,OP_SELL,lt,Bid,slp,Bid+slss*Point,Bidtpft*Point,cmt,mgc,0,clrDarkRed);
}
How the function is called:
Print(EACommentInj);
ticket_val_inj = Buy(lotsizeInj,slippageInj,stoplossInj,takeprofitInj,EACommentInj,MagicInj);
This is how it is initialised and it NEVER changes. It is mentioned only where it is passed. Where I showed you above.
const string EACommentInjGreed = "Holla v4.9 || GreedInjectionMode Greed Mode";
Although this is undocumented, the "string comment=NULL" parameter of the trade function OrderSend() in MQL4 is limited to 31 characters. If this limit is exceeded then the string is rejected as a whole and treated as NULL.
In your code, just before the OrderSend() function, add the following line:
cmt=StringSubstr(cmt,0,31);

How do I find the SourceLocation of the commas between function arguments using libtooling?

My main goal is trying to get macros (or even just the text) before function parameters. For example:
void Foo(_In_ void* p, _Out_ int* x, _Out_cap_(2) int* y);
I need to gracefully handle things like macros that declare parameters (by ignoring them).
#define Example _In_ int x
void Foo(Example);
I've looked at Preprocessor record objects and used Lexer::getSourceText to get the macro names In, Out, etc, but I don't see a clean way to map them back to the function parameters.
My current solution is to record all the macro expansions in the file and then compare their SourceLocation to the ParamVarDecl SourceLocation. This mostly works except I don't know how to skip over things after the parameter.
void Foo(_In_ void* p _Other_, _In_ int y);
Getting the SourceLocation of the comma would work, but I can't find that anywhere.
The title of the questions asks for libclang, but as you use Lexer::getSourceText I assume that it's libTooling. The rest of my answer is viable only in terms of libTooling.
Solution 1
Lexer works on the level of tokens. Comma is also a token, so you can take the end location of a parameter and fetch the next token using Lexer::findNextToken.
Here is a ParmVarDecl (for function parameters) and CallExpr (for function arguments) visit functions that show how to use it:
template <class T> void printNextTokenLocation(T *Node) {
auto NodeEndLocation = Node->getSourceRange().getEnd();
auto &SM = Context->getSourceManager();
auto &LO = Context->getLangOpts();
auto NextToken = Lexer::findNextToken(NodeEndLocation, SM, LO);
if (!NextToken) {
return;
}
auto NextTokenLocation = NextToken->getLocation();
llvm::errs() << NextTokenLocation.printToString(SM) << "\n";
}
bool VisitParmVarDecl(ParmVarDecl *Param) {
printNextTokenLocation(Param);
return true;
}
bool VisitCallExpr(CallExpr *Call) {
for (auto *Arg : Call->arguments()) {
printNextTokenLocation(Arg);
}
return true;
}
For the following code snippet:
#define FOO(x) int x
#define BAR float d
#define MINUS -
#define BLANK
void foo(int a, double b ,
FOO(c) , BAR) {}
int main() {
foo( 42 ,
36.6 , MINUS 10 , BLANK 0.0 );
return 0;
}
it produces the following output (six locations for commas and two for parentheses):
test.cpp:6:15
test.cpp:6:30
test.cpp:7:19
test.cpp:7:24
test.cpp:10:17
test.cpp:11:12
test.cpp:11:28
test.cpp:11:43
This is quite a low-level and error-prone approach though. However, you can change the way you solve the original problem.
Solution 2
Clang stores information about expanded macros in its source locations. You can find related methods in SourceManager (for example, isMacroArgExpansion or isMacroBodyExpansion). As the result, you can visit ParmVarDecl nodes and check their locations for macro expansions.
I would strongly advice moving in the second direction.
I hope this information will be helpful. Happy hacking with Clang!
UPD speaking of attributes, unfortunately, you won't have a lot of choices. Clang does ignore any unknown attribute and this behaviour is not tweakable. If you don't want to patch Clang itself and add your attributes to Attrs.td, then you're limited indeed to tokens and the first approach.

MQL4 storing indicator value

Does anyone know if it is possible to store the series of value of an indicator, over, for example 1 year, or of a boolean function calculated in an EA?
I would like tho store the value of a particular function calculated on the difference between two different EMA that I defined into an EA.
I need to store the value of this double function, calculated in my EA over few years (say from 2015 to 2017) and print it in some output file (.txt or some other formats)
int s15_60;
double B_M15_H1(int i) {
if (i>=0 && i<4 ) s15_60=0;
else if (i>=4 && i<8 ) s15_60=1;
else if (i>=8 && i<12 ) s15_60=2;
else if (i>=12 && i<16 ) s15_60=3;
else if (i>=16 && i<20 ) s15_60=4;
return NormalizeDouble(MathAbs(M15(i) - H1(s15_60)),Digits);
where M15 is a simple EMA calculated in the M15 timeframe, and H1 is the same EMA calculated in the H1 timeframe, and the double function is the distance between this two indicators calculated in M15 time steps.
My goal is to store this value in a output file for doing some statistical studies about this function.
EDIT:
This code works for my purpose:
#property copyright "Copyright 2014, MetaQuotes Software Corp."
#property link "https://www.mql5.com"
#property version "1.00"
#property strict
//--- show the window of input parameters when launching the script
#property script_show_inputs
//--- parameters for writing data to file
input string InpFileName="BOX.csv"; // File name
input string InpDirectoryName="Data"; // Folder name
//+------------------------------------------------------------------+
//| Script program start function |
//+------------------------------------------------------------------+
double H1 (int shift) {double val = iCustom(NULL,PERIOD_H1, "my_funct",100,2.0,30.0,2.0,2.0,0,1,0,shift); return(val);}
double H4 (int shift) {double val = iCustom(NULL,PERIOD_H4, "my_funct",100,2.0,30.0,2.0,2.0,0,1,0,shift); return(val);}
int s60_240;
double B_H1_H4(int i) {
if (i>=0 && i<4 ) s60_240=0;
else if (i>=4 && i<8 ) s60_240=1;
else if (i>=8 && i<12 ) s60_240=2;
else if (i>=12 && i<16 ) s60_240=3;
else if (i>=16 && i<20 ) s60_240=4;
return NormalizeDouble( 10000*MathAbs( H1(i) - H4(s60_240) ) , Digits);
}
void OnStart()
{
double box_buff[]; // array of indicator values
datetime date_buff[]; // array of indicator dates
//--- copying the time from last 1000 bars
int copied=CopyTime(NULL,PERIOD_H1,0,1000,date_buff);
ArraySetAsSeries(date_buff,true);
//--- prepare box_buff array
ArrayResize(box_buff,copied);
//--- copy the values of main line of the iCustom indicator
for(int i=0;i<copied;i++)
{
box_buff[i]=B_H1_H4(i);
}
//--- open the file for writing the indicator values (if the file is absent, it will be created automatically)
ResetLastError();
int file_handle=FileOpen(InpDirectoryName+"//"+InpFileName,FILE_READ|FILE_WRITE|FILE_CSV);
if(file_handle!=INVALID_HANDLE)
{
PrintFormat("%s file is available for writing",InpFileName);
PrintFormat("File path: %s\\Files\\",TerminalInfoString(TERMINAL_DATA_PATH));
//--- first, write the number of signals
FileWrite(file_handle,copied);
//--- write the time and values of signals to the file
for(int i=0;i<copied;i++)
FileWrite(file_handle,date_buff[i],box_buff[i]);
//--- close the file
FileClose(file_handle);
PrintFormat("Data is written, %s file is closed",InpFileName);
}
else
PrintFormat("Failed to open %s file, Error code = %d",InpFileName,GetLastError());
}
Please provide your MCVE-code to see what you need. How would you like to store data and why you might need it? Indicator data is already stored in a buffer so simply call it using iCustom(). If you want to optimize your EA and indicator take much time to load and compute buffers - yes it is possible to compute indicator buffers once then write them into a file or DB and get before new optimization starts, in such case use CArrayObj or CArrayDouble as a dynamic array for storing large arrays

Any suggestions about how to implement a BASIC language parser/interpreter?

I've been trying to implement a BASIC language interpreter (in C/C++) but I haven't found any book or (thorough) article which explains the process of parsing the language constructs. Some commands are rather complex and hard to parse, especially conditionals and loops, such as IF-THEN-ELSE and FOR-STEP-NEXT, because they can mix variables with constants and entire expressions and code and everything else, for example:
10 IF X = Y + Z THEN GOTO 20 ELSE GOSUB P
20 FOR A = 10 TO B STEP -C : PRINT C$ : PRINT WHATEVER
30 NEXT A
It seems like a nightmare to be able to parse something like that and make it work. And to make things worse, programs written in BASIC can easily be a tangled mess. That's why I need some advice, read some book or whatever to make my mind clear about this subject. What can you suggest?
You've picked a great project - writing interpreters can be lots of fun!
But first, what do we even mean by an interpreter? There are different types of interpreters.
There is the pure interpreter, where you simply interpret each language element as you find it. These are the easiest to write, and the slowest.
A step up, would be to convert each language element into some sort of internal form, and then interpret that. Still pretty easy to write.
The next step, would be to actually parse the language, and generate a syntax tree, and then interpret that. This is somewhat harder to write, but once you've done it a few times, it becomes pretty easy.
Once you have a syntax tree, you can fairly easily generate code for a custom stack virtual machine. A much harder project is to generate code for an existing virtual machine, such as the JVM or CLR.
In programming, like most engineering endeavors, careful planning greatly helps, especially with complicated projects.
So the first step is to decide which type of interpreter you wish to write. If you have not read any of a number of compiler books (e.g., I always recommend Niklaus Wirth's "Compiler Construction" as one of the best introductions to the subject, and is now freely available on the web in PDF form), I would recommend that you go with the pure interpreter.
But you still need to do some additional planning. You need to rigorously define what it is you are going to be interpreting. EBNF is great for this. For a gentile introduction EBNF, read the first three parts of a Simple Compiler at http://www.semware.com/html/compiler.html It is written at the high school level, and should be easy to digest. Yes, I tried it on my kids first :-)
Once you have defined what it is you want to be interpreting, you are ready to write your interpreter.
Abstractly, you're simple interpreter will be divided into a scanner (technically, a lexical analyzer), a parser, and an evaluator. In the simple pure interpolator case, the parser and evaluator will be combined.
Scanners are easy to write, and easy to test, so we won't spend any time on them. See the aforementioned link for info on crafting a simple scanner.
Lets (for example) define your goto statement:
gotostmt -> 'goto' integer
integer -> [0-9]+
This tells us that when we see the token 'goto' (as delivered by the scanner), the only thing that can follow is an integer. And an integer is simply a string a digits.
In pseudo code, we might handle this as so:
(token - is the current token, which is the current element just returned via the scanner)
loop
if token == "goto"
goto_stmt()
elseif token == "gosub"
gosub_stmt()
elseif token == .....
endloop
proc goto_stmt()
expect("goto") -- redundant, but used to skip over goto
if is_numeric(token)
--now, somehow set the instruction pointer at the requested line
else
error("expecting a line number, found '%s'\n", token)
end
end
proc expect(s)
if s == token
getsym()
return true
end
error("Expecting '%s', found: '%s'\n", curr_token, s)
end
See how simple it is? Really, the only hard thing to figure out in a simple interpreter is the handling of expressions. A good recipe for handling those is at: http://www.engr.mun.ca/~theo/Misc/exp_parsing.htm Combined with the aforementioned references, you should have enough to handle the sort of expressions you would encounter in BASIC.
Ok, time for a concrete example. This is from a larger 'pure interpreter', that handles a enhanced version of Tiny BASIC (but big enough to run Tiny Star Trek :-) )
/*------------------------------------------------------------------------
Simple example, pure interpreter, only supports 'goto'
------------------------------------------------------------------------*/
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>
#include <setjmp.h>
#include <ctype.h>
enum {False=0, True=1, Max_Lines=300, Max_Len=130};
char *text[Max_Lines+1]; /* array of program lines */
int textp; /* used by scanner - ptr in current line */
char tok[Max_Len+1]; /* the current token */
int cur_line; /* the current line number */
int ch; /* current character */
int num; /* populated if token is an integer */
jmp_buf restart;
int error(const char *fmt, ...) {
va_list ap;
char buf[200];
va_start(ap, fmt);
vsprintf(buf, fmt, ap);
va_end(ap);
printf("%s\n", buf);
longjmp(restart, 1);
return 0;
}
int is_eol(void) {
return ch == '\0' || ch == '\n';
}
void get_ch(void) {
ch = text[cur_line][textp];
if (!is_eol())
textp++;
}
void getsym(void) {
char *cp = tok;
while (ch <= ' ') {
if (is_eol()) {
*cp = '\0';
return;
}
get_ch();
}
if (isalpha(ch)) {
for (; !is_eol() && isalpha(ch); get_ch()) {
*cp++ = (char)ch;
}
*cp = '\0';
} else if (isdigit(ch)) {
for (; !is_eol() && isdigit(ch); get_ch()) {
*cp++ = (char)ch;
}
*cp = '\0';
num = atoi(tok);
} else
error("What? '%c'", ch);
}
void init_getsym(const int n) {
cur_line = n;
textp = 0;
ch = ' ';
getsym();
}
void skip_to_eol(void) {
tok[0] = '\0';
while (!is_eol())
get_ch();
}
int accept(const char s[]) {
if (strcmp(tok, s) == 0) {
getsym();
return True;
}
return False;
}
int expect(const char s[]) {
return accept(s) ? True : error("Expecting '%s', found: %s", s, tok);
}
int valid_line_num(void) {
if (num > 0 && num <= Max_Lines)
return True;
return error("Line number must be between 1 and %d", Max_Lines);
}
void goto_line(void) {
if (valid_line_num())
init_getsym(num);
}
void goto_stmt(void) {
if (isdigit(tok[0]))
goto_line();
else
error("Expecting line number, found: '%s'", tok);
}
void do_cmd(void) {
for (;;) {
while (tok[0] == '\0') {
if (cur_line == 0 || cur_line >= Max_Lines)
return;
init_getsym(cur_line + 1);
}
if (accept("bye")) {
printf("That's all folks!\n");
exit(0);
} else if (accept("run")) {
init_getsym(1);
} else if (accept("goto")) {
goto_stmt();
} else {
error("Unknown token '%s' at line %d", tok, cur_line); return;
}
}
}
int main() {
int i;
for (i = 0; i <= Max_Lines; i++) {
text[i] = calloc(sizeof(char), (Max_Len + 1));
}
setjmp(restart);
for (;;) {
printf("> ");
while (fgets(text[0], Max_Len, stdin) == NULL)
;
if (text[0][0] != '\0') {
init_getsym(0);
if (isdigit(tok[0])) {
if (valid_line_num())
strcpy(text[num], &text[0][textp]);
} else
do_cmd();
}
}
}
Hopefully, that will be enough to get you started. Have fun!
I will certainly get beaten by telling this ...but...:
First, I am actually working on a standalone library ( as a hobby ) that is made of:
a tokenizer, building linear (flat list) of tokens from the source text and following the same sequence as the text ( lexems created from the text flow ).
A parser by hands (syntax analyse; pseudo-compiler )
There is no "pseudo-code" nor "virtual CPU/machine".
Instructions(such as 'return', 'if' 'for' 'while'... then arithemtic expressions ) are represented by a base c++-struct/class and is the object itself. The base object, I name it atom, have a virtual method called "eval", among other common members, that is the "execution/branch" also by itself. So no matter I have an 'if' statement with its possible branchings ( single statement or bloc of statements/instructions ) as true or false condition, it will be called from the base virtual atom::eval() ... and so on for everything that is an atom.
Even 'objects' such as variables are 'atom'. 'eval()' will simply return its value from a variant container held by the atom itself ( pointer, refering to the 'local' variant instance (the instance variant iself) held the 'atom' or to another variant held by an atom that is created in a given 'bloc/stack'. So 'atom' are 'inplace' instructions/objects.
As of now, as an example, chunk of not really meaningful 'code' as below just works:
r = 5!; // 5! : (factorial of 5 )
Response = 1 + 4 - 6 * --r * ((3+5)*(3-4) * 78);
if (Response != 1){ /* '<>' also is not equal op. */
return r^3;
}
else{
return 0;
}
Expressions ( arithemtics ) are built into binary tree expression:
A = b+c; =>
=
/ \
A +
/ \
b c
So the 'instruction'/statement for expression like above is the tree-entry atom that in the above case, is the '=' (binary) operator.
The tree is built with atom::r0,r1,r2 :
atom 'A' :
r0
|
A
/ \
r1 r2
Regarding 'full-duplex' mecanism between c++ runtime and the 'script' library, I've made class_adaptor and adaptor<> :
ex.:
template<typename R, typename ...Args> adaptor_t<T,R, Args...>& import_method(const lstring& mname, R (T::*prop)(Args...)) { ... }
template<typename R, typename ...Args> adaptor_t<T,R, Args...>& import_property(const lstring& mname, R (T::*prop)(Args...)) { ... }
Second: I know there are plenty of tools and libs out there such as lua, boost::bind<*>, QML, JSON, etc... But in my situation, I need to create my very own [edit] 'independant' [/edit] lib for "live scripting". I was scared that my 'interpreter' could take a huge amount of RAM, but I am surprised that it is not as big as using QML,jscript or even lua :-)
Thank you :-)
Don't bother with hacking a parser together by hand. Use a parser generator. lex + yacc is the classic lexer/parser generator combination, but a Google search will reveal plenty of others.

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