cogent/examples/bag/main.ac

// In this example, we intentially avoid using the standard Cogent library.
// Everything is defined locally (apart from the built-in types in Cogent).

$esc:(#include <stdlib.h>)
$esc:(#include <stdio.h>)

typedef void* Heap;

#include "generated.c"

$ty:(< Failure Heap | Success (Bag, Heap) >) newBag ($ty:(Heap) heap)
{
  $ty:(< Failure Heap | Success (Bag, Heap) >) ret;
  $ty:(Bag) bag = malloc (sizeof (*bag));
  
  if (!bag) {
    ret.tag = TAG_ENUM_Failure;
    ret.Failure = heap;
    return ret;
  }

  bag->count = 0;
  bag->sum = 0; 

  ret.tag = TAG_ENUM_Success;
  ret.Success.p1 = bag;
  ret.Success.p2 = heap;
  return ret;
}

$ty:(Heap) freeBag ($ty:((Heap, Bag)) args)
{
  free (args.p2);  // free the Bag
  return args.p1;  // return the "new" Heap
}


$ty:b $id:reduce ($ty:(((List a)!, (a!, b) -> b, b)) args)
{
  $ty:((List a)) list = args.p1;
  $ty:b acc = args.p3;  // Initial accummulator

  $ty:((a!, b)) fargs;

  while (list) {
    fargs.p1 = list->data;
    fargs.p2 = acc;
    acc = (($spec:((a!, b) -> b)) args.p2) (fargs);
    list = list->next;
  }

  return acc;
}



int main ()
{
  // Create a list of a few U32 integers.
  // As we don't have a function for initialising a list in Cogent,
  // we cannot define a poly-function in antiquoted C. That's why here
  // we only implement an instance of it, hackily.

  $ty:(List U32) list = NULL;

  $ty:(U32) x = 0;
  while (1) {
    printf("Enter a number: ");
    if (scanf("%d",&x) < 0) {
      break;
    }
    $ty:(List U32) cell = malloc (sizeof (*cell));
    cell->data = x;
    cell->next = list;
    list = cell;
  }

  // Print the list

  $ty:(List U32) curr;
  curr = list;

  printf ("\nThe list is: ");
  while (curr != NULL) {
    printf ("%d -> ", curr->data);
    curr = curr->next;
  }
  printf ("NULL\n");  

  // Now call `average'
  $ty:((Heap, (List U32)!)) avg_args;
  avg_args.p1 = NULL;
  avg_args.p2 = list;
  $ty:((Heap, U32)) avg_ret = $exp:(average) (avg_args);
  printf("The average is: %d\n", avg_ret.p2);

  return 0;
}