Call Racket function from C - c

Question

I have a Racket module hw.rkt:
#lang racket/base
(provide hw)
(define (hw) (displayln "Hello, world!"))
I would like to write a C program that embeds the Racket runtime and applies the procedure (hw).
There is example code here which demonstrates how to embed the Racket runtime and apply a procedure that is in racket/base, or to read and evaluate an S-expression, but I've had no luck modifying this code to allow access to the (hw) procedure.
This page seems to say that it is possible to do what I want to do by first compiling hw.rkt to hw.c using raco ctool --c-mods, and this works just fine when I try it, but I still can't actually access the (hw) procedure.
If someone could post a complete example program, or simply describe which C functions to use, I would be very appreciative. From there I can figure out the rest.
Editing to provide examples of things I have tried.
I modified the example program to get rid of the "evaluate command line arguments" bit and skip straight to the REPL so that I could experiment. Thus (with "hw.c" the result of running raco ctool --c-mods hw.c ++libs racket/base hw.rkt):
#define MZ_PRECISE_GC
#include "scheme.h"
#include "hw.c"
static int run(Scheme_Env *e, int argc, char *argv[])
{
Scheme_Object *curout = NULL, *v = NULL, *a[2] = {NULL, NULL};
Scheme_Config *config = NULL;
int i;
mz_jmp_buf * volatile save = NULL, fresh;
MZ_GC_DECL_REG(8);
MZ_GC_VAR_IN_REG(0, e);
MZ_GC_VAR_IN_REG(1, curout);
MZ_GC_VAR_IN_REG(2, save);
MZ_GC_VAR_IN_REG(3, config);
MZ_GC_VAR_IN_REG(4, v);
MZ_GC_ARRAY_VAR_IN_REG(5, a, 2);
MZ_GC_REG();
declare_modules(e);
v = scheme_intern_symbol("racket/base");
scheme_namespace_require(v);
config = scheme_current_config();
curout = scheme_get_param(config, MZCONFIG_OUTPUT_PORT);
save = scheme_current_thread->error_buf;
scheme_current_thread->error_buf = &fresh;
if (scheme_setjmp(scheme_error_buf)) {
scheme_current_thread->error_buf = save;
return -1; /* There was an error */
} else {
/* read-eval-print loop, uses initial Scheme_Env: */
a[0] = scheme_intern_symbol("racket/base");
a[1] = scheme_intern_symbol("read-eval-print-loop");
v = scheme_dynamic_require(2, a);
scheme_apply(v, 0, NULL);
scheme_current_thread->error_buf = save;
}
MZ_GC_UNREG();
return 0;
}
int main(int argc, char *argv[])
{
return scheme_main_setup(1, run, argc, argv);
}
Things that don't work (and their error messages):
Calling (hw) from the REPL
hw: undefined:
cannot reference undefined identifier
context...:
/usr/local/share/racket/collects/racket/private/misc.rkt:87:7
((dynamic-require 'hw 'hw))
standard-module-name-resolver: collection not found
for module path: hw
collection: "hw"
in collection directories:
context...:
show-collection-err
standard-module-name-resolver
/usr/local/share/racket/collects/racket/private/misc.rkt:87:7
((dynamic-require "hw.rkt" 'hw))
standard-module-name-resolver: collection not found
for module path: racket/base/lang/reader
collection: "racket/base/lang"
in collection directories:
context...:
show-collection-err
standard-module-name-resolver
standard-module-name-resolver
/usr/local/share/racket/collects/racket/private/misc.rkt:87:7
Editing the example code
v = scheme_intern_symbol("racket/base");
scheme_namespace_require(v);
v = scheme_intern_symbol("hw");
scheme_namespace_require(v);
Error:
standard-module-name-resolver: collection not found
for module path: hw
collection: "hw"
in collection directories:
context...:
show-collection-err
standard-module-name-resolver
SIGSEGV MAPERR sicode 1 fault on addr 0xd0
Aborted
(The segfault was probably because I didn't check the value of 'v' before trying to scheme_namespace_require it.)
Editing the example code mk. 2
v = scheme_intern_symbol("racket/base");
scheme_namespace_require(v);
v = scheme_intern_symbol("hw.rkt");
scheme_namespace_require(v);
Error:
hw.rkt: bad module path
in: hw.rkt
context...:
standard-module-name-resolver
SIGSEGV MAPERR sicode 1 fault on addr 0xd0
Aborted
(re: segfault: as above)
Editing the example code mk. 3
v = scheme_intern_symbol("racket/base");
scheme_namespace_require(v);
v = scheme_intern_symbol("./hw.rkt");
scheme_namespace_require(v);
(as above)
Editing the example code mk. 4
/* read-eval-print-loop, uses initial Scheme_Env: */
a[0] = scheme_intern_symbol("hw");
a[1] = scheme_intern_symbol("hw");
v = scheme_dynamic_require(2, a);
(as mk. 1, save the segfault)
Editing the example code mk. 5
/* read-eval-print loop, uses initial Scheme_Env: */
a[0] = scheme_intern_symbol("hw");
a[1] = scheme_eval(a[0], e);
scheme_apply(a[1], 0, NULL);
Error:
hw: undefined;
cannot reference undefined identifier

Answer 1

Answered by Matthew Flatt here. When using dynamic-require, I needed to quote the name of the module twice, not once. Thanks to Dr. Flatt for their assistance.