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Trivial Janet project with a bundled native C module

Blog 2020/7/29

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Trivial Janet project with a bundled native C module

This is the simplest example of how to write a Janet project which is a mixture of C and Janet, which results in a single, statically-linked executable.

Run make to build and test the executable build/baz.

Details

foo.c is a Janet native C module which implements a namespace foo, which contains one function bar, which returns the number 42.

To build and test this module, run make test-foo. You can also start a interactive REPL with this module imported via make repl-foo (type (foo/bar) at the prompt).

baz.janet is a Janet program which imports the foo module, then prints foo/bar multiplied by 2.

To build and test the build/baz statically-linked executable, run make test-baz, or simply make.

(import build/foo :as foo)
(defn main [& args]
(print (* 2 (foo/bar))))
// Trivial Janet native module which contains one function which returns 42.
#include <janet.h>
static Janet cfun_foo_bar(int32_t argc, Janet *argv) {
return janet_wrap_number(42);
}
static const JanetReg cfuns[] = {
{
"bar", cfun_foo_bar,
"(foo/bar)\n\nReturns 42."
},
{NULL, NULL, NULL}
};
JANET_MODULE_ENTRY(JanetTable *env) {
janet_cfuns(env, "foo", cfuns);
}
default: test-foo test-baz
build/foo.a: foo.c
jpm --verbose build
test-foo: build/foo.a
test 42 = $(shell janet -e '(import build/foo :as foo) (print (foo/bar))')
repl-foo: build/foo.a
janet -e '(import build/foo :as foo)' -r
build/baz: build/foo.a baz.janet
jpm --verbose build
test-baz: build/baz
test 84 = $(shell ./build/baz)
clean:
rm -rf build
.PHONY: default test-foo repl-foo test-baz clean
(declare-project
:name "baz")
(declare-native
:name "foo"
:source @["foo.c"]
:cflags [;default-cflags "-Wno-unused-parameter"])
(declare-executable
:name "baz"
:entry "baz.janet")
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@pyrmont pyrmont commented Jul 30, 2020

This is really helpful. Thanks for sharing it!

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