[m-users.] Segmentation violation on FFI wrapper for linenoise-ng

[Sean Charles (emacstheviking)]

Beautiful. It took me a while to read and assimilate it but it definitely feels more like ’The Way’.

I’ve learned a lot today!

I made the suggested changes, there is an errant ‘dot’ after ok(string) in the ln_read_result declaration, the foreign export needed to be `raw_ln_result/0` not ln_result/0 and the implementation of ln_read needed to use raw_ln_result.

Apart from that, absolute perfection. It’s in, built and working wonderfully, thank you!

Sean.

PS: You are now immortalised in a got comment. :)


> On 19 Jun 2021, at 15:11, Julien Fischer <jfischer at opturion.com> wrote:
> 
> 
> 
> On Sat, 19 Jun 2021, Sean Charles (emacstheviking) wrote:
> 
>> WAAAAAT!
>> 
>> :facepalm:
>> 
>> I took that print line out, removed ’the fix’/…….I don’t think I need tell you how it went.
>> 
>> Sometimes it never fails to baffle me, after 35 years, that sometimes you can fail to read and understand your own code.
>> 
>> :D
>> 
>> Sigh… you live and learn. I hope.
>> 
>> Thanks Julien, I am going outside to self-flagellate with some nettles I mowed down this morning…..
> 
> For the record, I would probably wrap the linenoise() function as in the
> following (untested) code:
> 
>    :- type ln_read_result
>        --->  ok(string).
>        ;     eof.
> 
>    :- pred ln_read(string::in, ln_read_result::out, io::di, io::uo) is det.
> 
>    ln_read(Prompt, Result, !IO) :-
>        do_ln_read(Prompt, RawResult, Line, !IO),
>        (
>            RawResult = ok,
>            Result = ok(Line)
>        ;
>            RawResult = eof,
>            Result = eof
>        ).
> 
>     :- type raw_ln_result
>        --->     ln_result_ok
>        ;        ln_result_eof.
> 
>     :- pragma foreign_export_enum("C", ln_result/0, [uppercase]).
> 
>     :- pragma foreign_decl("C", "#include ""mercury_string.h""").
> 
>     :- pred do_ln_read(string::in, raw_ln_result::out, string::out, io::di, io::uo)
>         is det.
> 
>     :- pragma foreign_proc( "C",
>         do_ln_read(Prompt::in, Result::out, Line::out, _IO0::di, _IO::uo),
>         [will_not_throw_exception, promise_pure, tabled_for_io],
>     "
>         char* line = linenoise((const char*) Prompt);
>         if (line) {
>             linenoiseHistoryAdd(line);
>             Result = LN_RESULT_OK;
>             // Copy the string on to the Mercury heap.
>             MR_make_aligned_string_copy(Line, line);
>         } else {
>             Result = LN_RESULT_EOF;
>             // Set Line to a valid value so we do not crash the
>             // debugger.
>             Line = MR_make_string_const("""");
>         }
>     ").
> 
> Julien.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mercurylang.org/archives/users/attachments/20210619/3600d206/attachment-0001.html>