Extending C with cmacro
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anaphoric
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README.rst

README.rst

Magma: cmacro extensions to C

Overview

C is a tremendously useful language: It compiles everywhere, is generally fast, has a very long history and a stable standard, and comes with few bedrock abstractions.

Higher-level languages, like Common Lisp and Haskell, provide excellent metaprogramming systems and a very expressive type system, but have the cost of various bedrock abstractions like garbage collection, dynamic typing (In the case of Lisp), and exception handling.

cmacro provides a middleground: It bridges the power and control of C with the high-level metaprogramming systems of Lisp. This library uses cmacro to extend the capabilities of the C language.

Usage

Once you've built and installed cmacro, simply put these files in a directory where they can be included by cmacro.

Functions

Anonymous Functions

Syntax

lambda (<args>*) -> <ret> { <body>* }

Description

Defines an anonymous function, returning a pointer to it.

Examples

cmacro_import "fn/lambda.c"

int main() {
  int array[] = {423, 61, 957, 133, 969,
                 829, 821, 390, 704, 596};

  qsort(array, 10, sizeof(int),
        lambda (const void* a, const void* b) -> int
        { return *(int*)a - *(int*)b; });
  for(size_t i = 0; i < 10; i++){
    printf("%i ", array[i]);
  }
  return 0;
}

Lazy Evaluation

Syntax

  • delay <expr>
  • force <expr>

Description

delay takes an expression expr and delays its computation until the required time. force takes this computation and executes it, returning its value.

Examples

force (delay 1) == 1;

Type System

Type-Inferenced Variables

Syntax

var <name> = <value>

Description

Defines an implicitly-typed variable var, giving it the value value. It is not possible to define a variable without an initial value.

Examples

/* Input */
cmacro_import "type/var.c"

void f() {
  var a = 10;
  var b = 3.14;
}

/* Output */
void f() {
  typeof(10) a = 10;
  typeof(3.14) b = 3.14;
  /* The above is, in fact, valid */
}

Algebraic Data Types

Syntax

Description

Examples

#include <stdio.h>

cmacro_import "type/adt.c"

data Token {
  Integer { int i; };
  String  { char* str; };
}

int main() {
  Token a, b;
  construct(a, Token -> Integer) { 10 };
  construct(b, Token -> String) { "test" };
  switch(a.type) {
    case TokenInteger:
      return a.Integer.i;
      break;
    case TokenString:
      puts(b.String.str);
      break;
  }
}

Tuples

Syntax

Description

Examples

/* Input */
cmacro_import "type/tuple.c"

typedef tup(int, int) pair;

pair divrem(int n, int d) {
  return (pair){n/d, n%d};
}

/* Output */
typedef struct { int first; int second; } pair;

pair divrem(int n, int d) {
  return (pair){n/d, n%d};
}

Anaphoric Macros

Anaphoric macros store the output of an important argument (Like the condition in the if statement) in a variable named it so they can be accessed in the statement body.

if

Syntax

  • aif <cond> <true-branch>
  • aif <cond> <true-branch> else <false-branch>

Description

The value of cond is stored in the variable it, which is accessible in the scope of either branch.

Examples

/* Input */
cmacro_import "anaphoric/if.c"

int main() {
  aif(5 > 1)
    return it;
}


/* Output */
int main() {
  typeof(5 > 1) it = 5 > 1;
  if(it)
    return it;
}

Utilities

doto

Syntax

doto(obj) { <fn>(<args>*);+ }

Description

Calls every fn, with obj appended to the beginning of its argument list.

Examples

/* Input */
cmacro_import "util/doto.c"

void cancelAccount(Account* account) {
  doto(account) {
    setBalance(0);
    setStatus(DISABLED);
  }
}

/* Output */
void cancelAccount(Account* account) {
  setBalance(account, 0);
  setStatus(account, DISABLED);
}

with_allocation

Syntax

  • with_allocation(<ptr>, <type>) { <body>* }
  • with_allocation(<ptr>, <type>, <length>) { <body>* }

Description

Allocates memory to hold type, optionally an array of type if length is specified. The pointer is stored in the variable ptr and free'd after body is executed.

Examples

cmacro_import "util/with_allocation.c"

int main() {
  with_allocation(ptr, int, 10) {
    size_t i;
    for(i = 0; i < 10; i++) {
      ptr[i] = i*2;
    }
  }
  with_allocation(p, int) {
    *p = 10;
    return *p;
  }
}

with_open_file

Syntax

with_open_file(<stream>, <filepath>, <mode>) { <body>* }

Description

Opens filepath with mode mode, assigning it to the variable stream, then executes body and closes the stream.

Examples

cmacro_import "util/with_open_file.c"

int main() {
  with_open_file(file, "README.md", "r") {
    printf("The first character in the README is: %c\n",
           fgetc(file));
  }
  return 0;
}

License

Copyright (c) 2014 Fernando Borretti (eudoxiahp@gmail.com)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.