Scramble

About

Scramble is a C preprocessor which allows to write C code which looks a bit like Python code with a full Python3 environment available for meta programming. That is, no semantics at all are changed - when using Scramble you still write C code. But it has a syntax more similar to Python.

Similar (and better) projects:

• pyrex
• shedskin
• pypy
• pyplus

Example

Scramble is used like this:

scramble.py -i input.py -c output.c -h output.h -n name

For example, if you have a file main.py, then you could run:

scramble.py -i src/main.py -c build/c/main.c -h build/h/main.h -n main

And if your src/main.py would look like to the left, the resulting files would look like to the right:

import stdio, string, math

def main(int argc, char **argv) -> int:
    if argc == 2:
        printf("%f\n", sin(strtod(argv[1]))
        return 0
    else:
        fprintf(stderr, "Need exactly one argument!\n")
        return 1

#include "main.h"

int main(int argc, char **argv)
{
    if (argc == 2) {
        printf("%f\n", sin(strtod(argv[1]));
        return 0;
    }
    else {
        fprintf(stderr, "Need exactly one argument!\n");
        return 1;
    }
}

#ifndef _MAIN_

#include "stdio.h"
#include "string.h"
#include "math.h"

extern int main(int argc, char **argv);

#endif

Keywords

All C, C++ and Python keywords basically are also Scramble keywords. The following control flow constructs are used by scramble: while, switch...case, do...while, for X while Y with Z [for (X; Y; Z) in C], for...in, if...elif...else, label [: in C], goto.

And these declarations: class [struct in C], def, enum, global, import, macro [#define in C], static, struct, typedef, union.

These Python operators are used instead of the C++ ones: and [&& in C], max, min, not [! in C], or [|| in C].

And there's a few new constants: True, False, None.

Features

In general, here is what scramble will do:

• No more ; required.
• : and indentation instead of { and }.

• No ( and ) for builtin C keywords like if. For example:

  if x == 2: x = 3 y = 3

  translates to

  if (x == 2) { x = 3; y = 2; }

• Use elif instead of else if, like in python.

• Use and, or and not inside conditionals, like in python.

• Functions are declared with def, and parameter types can be grouped. For example:

  def f1(): pass def f2(int x, y, z): pass def f3 -> int: pass

  translates to

  void f1(void) { } void f2(int x, int y, int z) { } int f3(void) { }

• Headers are generated automatically. This works by outputting a declaration for each function or global variable which is not declared static. Similarly, struct/union/enum declarations are written into the header unless declared static, and a type is automatically defined for them. For example:

  test.py class A: int x class B: A *a static class C: B *b static def a_new() -> A: A self = calloc(1, sizeof *self) return self def b_new() -> B: B self = calloc(1, sizeof *self) self->a = a_new() return self

  translates to

  test.c #include "test.h" typedef struct C C; struct C { B *b; }; static A a_new(void) { A self = calloc(1, sizeof *self); return self; } B b_new(void) { B self = calloc(1, sizeof *self); self->a = a_new(); return self; } and test.h #ifndef TEST typedef struct A A; typedef struct B B; struct A { int x; }; struct B { A *a; }; B *a_new(void); endif

• Comments are started with #.

• Include files are included with import. For example:

  import test, global stdio

  translates to

  #include "test.h" include <stdio.h>

• Meta programming using full Python. This is possibly the single most useful feature - at compile time you have the full Python interpreter at your disposal to create any code you want.

  ***scramble for x in ["A", "B", "C"]: parse("char def function" + x + "(): return '" + x + "'")

  translates to

  char functionA(void) { return 'A'; } char functionB(void) { return 'B'; } char functionC(void) { return 'C'; }

• Triple quoted strings, useful for multi-line string constants.

• Support for auto declarations (type is inferred)
• In many cases you can use . instead of -> (if the type inference sees a pointer left of the . a -> is output instead)

• Extended for-loop syntax, for example:

  MyArray arr for MyElem x in arr: handle(x)

  translates to

  MyArrayIterator iter = MyArrayIterator_first(arr); for (MyElem *x = MyArrayIterator_item(arr, &iter); MyArrayIterator_next(arr, &iter); x = MyArrayIterator_item(arr, &iter)) { handle(x); }

• Docstrings can be used to automatically generate documentation. Strings at the beginning of a function are ignored, but can optionally be output to a separate file, associated with the function they are defined in. This can then be used to translate into different documentation formats.

More stuff (might change?)

• None, min, max, True, False keywords. For now min and max are macros for the ternary operator - with the usual problem of evaluating the argument twice.
• As the hash sign starts a comment, *** can be used to insert C preprocessor commands.
• Instead of #define, macro and static macro can be used to place a #define either into the .h or .c file.
• Since the : is used up by Python syntax, labels are marked with the label keyword instead of :. Bitfields use the keyword with. The colon in the C tertiary operator works for now until I implemnt the if-else construct.