cogent/examples/iterator/main.ac

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

/*
 * The environment is an opaque type known only to the C implementation.
 *
 * It is actually empty but is needed by the cogent to demonstrate that
 * there is some value that is being changed by the operations on things
 * outside of the code itself.
 *
 * It essentially represents 'the world' to the program.
 */
typedef void *Env;

/*
 * This is how we embed the code generated by the cogent compiler.
 *
 * The makefile is configured to ensure the cogent output is produced as
 * 'generated.c'.
 */
#include "generated.c"

/*
 * Our implementation of show_u32 just prints the value using printf.
 * We need to pass the environment back afterwards which was 'mutated'
 * by the act of printing to standard output.
 */
$ty:(Env) show_u32 ($ty:((Env, U32)) args) {
	printf("%d", args.p2);
	return args.p1;
}

/*
 * As above but for strings being printed directly.
 */
$ty:(Env) show_string ($ty:((Env, String)) args) {
	fputs(args.p2, stdout);
	return args.p1;
}

/*
 * This implementation of iterate is fairly straightforward. The
 * iterator is just a starting value, a condition function, and the loop
 * body. We just plug all of the sections into the appropriate parts of
 * a while loop and let it run.
 */
$ty:(a) $id:iterate ($ty:(Iterator a) iter) {
	$ty:(a) curr = iter.curr;
	$ty:(<Continue | Stop>) proceed;

	proceed = (($spec:(IterCondition a)) iter.condition) (curr);
	while (proceed.tag == TAG_ENUM_Continue) {
		curr = (($spec:(IterStep a)) iter.step) (curr);
		proceed = (($spec:(IterCondition a)) iter.condition) (curr);
	}

	/*
	 * We need to return the final value of the loop. This is especially
	 * important if it is or contains any heap values that would
	 * otherwise be leaked but this also contains all of the information
	 * for what has actually occurred in the loop.
	 */
	return curr;
}

/*
 * Main here just creates 'the world' and passes it to the cogent
 * program. The cogent program mutates it and we get the result.
 */
int main(void) {
	$ty:(Env) env = NULL;
	env = $esc:prog(env);

	return EXIT_SUCCESS;
}