Stackless coroutine compiler for C
Unstructured state machines are not a good solution for asynchronous logic. They
have all the same problems as goto making the logic of your program very difficult
to follow. This compiler allows you to add stackless coroutines to your C program.
These coroutines enable you to structure your asynchronous logic in a more readable
and maintainable way.
cd src; make
{%
struct example_s {
int i;
int count_twice;
};
void increment(struct example_s* ctx) {
ctx->i++;
}
int twice(struct example_s* ctx) {
return ctx->count_twice;
}
%} //inject raw c into your program
//define the return type, name and argument type of the coroutine
coroutine (int) count_to_five(struct example_s*) {
if twice { //conditions can be calls to procedures like this or raw c
//use {% and %} to drop down to C when convenient the argument can be accessed via arg
{% arg->i = 0; %}
call count; //call subroutines with the call keyword
{% arg->i = 0; %}
call count;
} else {
{% arg->i = 0; %}
call count;
}
}
sub count { //define a subroutine
while {% arg->i <= 5 %} {
increment; //call procedures that operate on the argument
yield {% arg->i; %}; //yield a return value
}
}
{%
int main() {
int state = 0; //stores the state of the coroutine
struct example_s ctx = { .i = 0, .count_twice = 1 };
//corc generates a procedure that takes an int pointer and the argument type
call_count_to_five(&state, &ctx); //returns 1
call_count_to_five(&state, &ctx); //returns 2
call_count_to_five(&state, &ctx); //returns 3
call_count_to_five(&state, &ctx); //returns 4
call_count_to_five(&state, &ctx); //returns 5
call_count_to_five(&state, &ctx); //returns 1
call_count_to_five(&state, &ctx); //returns 2
call_count_to_five(&state, &ctx); //returns 3
call_count_to_five(&state, &ctx); //returns 4
call_count_to_five(&state, &ctx); //returns 5
call_count_to_five(&state, &ctx); //returns undefined int, state will be -1;
assert(state == -1);
}
%}The compiler operates on standard input and output. To compile this program:
corc < example.co > example.c
Take a look at examples/echo.co for a more real world example that implements
fibers and an echo server on top of libev.