Readme.md

How to run:

Install lean4 (using elan), and run:

lean --c=hello.c hello.lean

hello.c

// Lean compiler output
// Module: hello
// Imports: Init
#include <lean/lean.h>
#if defined(__clang__)
#pragma clang diagnostic ignored "-Wunused-parameter"
#pragma clang diagnostic ignored "-Wunused-label"
#elif defined(__GNUC__) && !defined(__CLANG__)
#pragma GCC diagnostic ignored "-Wunused-parameter"
#pragma GCC diagnostic ignored "-Wunused-label"
#pragma GCC diagnostic ignored "-Wunused-but-set-variable"
#endif
#ifdef __cplusplus
extern "C" {
#endif
lean_object* l_getOrOne(lean_object*);
lean_object* l_getOrOne_match__1(lean_object*);
lean_object* l_getOrOne___boxed(lean_object*);
lean_object* l_getOrOne_match__1___rarg(lean_object*, lean_object*, lean_object*);
lean_object* l_getOrOne_match__1___rarg(lean_object* x_1, lean_object* x_2, lean_object* x_3) {
_start:
{
if (lean_obj_tag(x_1) == 0)
{
lean_object* x_4; lean_object* x_5; 
lean_dec(x_3);
x_4 = lean_box(0);
x_5 = lean_apply_1(x_2, x_4);
return x_5;
}
else
{
lean_object* x_6; lean_object* x_7; 
lean_dec(x_2);
x_6 = lean_ctor_get(x_1, 0);
lean_inc(x_6);
lean_dec(x_1);
x_7 = lean_apply_1(x_3, x_6);
return x_7;
}
}
}
lean_object* l_getOrOne_match__1(lean_object* x_1) {
_start:
{
lean_object* x_2; 
x_2 = lean_alloc_closure((void*)(l_getOrOne_match__1___rarg), 3, 0);
return x_2;
}
}
lean_object* l_getOrOne(lean_object* x_1) {
_start:
{
if (lean_obj_tag(x_1) == 0)
{
lean_object* x_2; 
x_2 = lean_unsigned_to_nat(1u);
return x_2;
}
else
{
lean_object* x_3; 
x_3 = lean_ctor_get(x_1, 0);
lean_inc(x_3);
return x_3;
}
}
}
lean_object* l_getOrOne___boxed(lean_object* x_1) {
_start:
{
lean_object* x_2; 
x_2 = l_getOrOne(x_1);
lean_dec(x_1);
return x_2;
}
}
lean_object* initialize_Init(lean_object*);
static bool _G_initialized = false;
lean_object* initialize_hello(lean_object* w) {
lean_object * res;
if (_G_initialized) return lean_io_result_mk_ok(lean_box(0));
_G_initialized = true;
res = initialize_Init(lean_io_mk_world());
if (lean_io_result_is_error(res)) return res;
lean_dec_ref(res);
return lean_io_result_mk_ok(lean_box(0));
}
#ifdef __cplusplus
}
#endif

hello.lean

inductive MaybeNat where
 | None
 | Just (n: Nat)
 
open MaybeNat
 
def getOrOne (m:MaybeNat) : Nat :=
    match m with
        | None => 1
        | Just n => n