Handling noreturn functions

[Shea Levy]

Hi all,

Some functions (like C's exit(3) or longjmp(3)) never return. Is there a
way to mark them as such in ATS so that a non-void function can call
them without having to construct a fake value to return after the call?

e.g. is there some way I can write:

> fn foo(bool b): int = if b then 1 else perror "bad value"; exit(1)

without sequencing the exit with some constructed value that I know will
never actually be returned?

~Shea

[gmhwxi]

It works if you write:

fn foo{b:bool}(b: bool b): int =
  if b then 1 else (perror "bad value"; exit(1))

For any type T, exit(1){T} is considered by the typechecker a value of the type T. So you can write:

fn foo{b:bool}(b: bool b): int =
  if b then 1 else (perror "bad value"; exit(1){int})

[Shea Levy]

Ah ha! I see that's implemented by making exit a template and
implementing it as a macro. My attempt to implement something similar
with an infinte loop failed:

> fun loop (): {a: t@ype}(a) = loop ()
> implement main () = loop ()

Gives:

> test_dats.c:119:1: error: ‘loop_0’ declared as function returning an array

during c compilation. Do I have to resort to a macro/function in C here?

~Shea

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[gmhwxi]

Notice that the size of the type T = {a:t@ype}(a) is unknown, so
the compiler cannot generate proper C code for 'loop' (it is no problem
to generate JavaScript code, though). So you need a special way to implement
such a function for use in C.

[Shea Levy]

Ah, right. I wonder if something like:

> #define FAKE_VAL(ty) *((ty *) NULL)

could be done in ATS?

~Shea

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[gmhwxi]

How about

ptr0_get<ty>(the_null_ptr)

[Shea Levy]

Perfect!

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