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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: Command line globber/tokenizer library for C?
Date: Mon, 16 Sep 2024 00:52:26 -0700
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Michael S <already5chosen@yahoo.com> writes:

[comments reordered]

> Also, while formally the program is written in C,  by spirit it's
> something else.  May be, Lisp.

I would call it a functional style, but still C.  Not a C style
as most people are used to seeing it, I grant you that.  I still
think of it as C though.


> Lisp compilers are known to be very good at tail call elimination.
> C compilers also can do it, but not reliably.  In this particular
> case I am afraid that common C compilers will implement it as
> written, i.e. without turning recursion into iteration.

I routinely use gcc and clang, and both are good at turning
this kind of mutual recursion into iteration (-Os or higher,
although clang was able to eliminate all the recursion at -O1).
I agree the recursion elimination is not as reliable as one
would like;  in practice though I find it quite usable.


> Tested on godbolt.
> gcc -O2 turns it into iteration starting from v.4.4
> clang -O2 turns it into iteration starting from v.4.0

Both as expected.

> Latest icc still does not turn it into iteration at least along one
> code paths.

That's disappointing, but good to know.

> Latest MSVC implements it as written, 100% recursion.

I'm not surprised at all.  In my admittedly very limited experience,
MSVC is garbage.


> Can you give an example implementation of go->f() ?
> It seems to me that it would have to use CONTAINING_RECORD or
> container_of or analogous non-standard macro.

You say that like you think such macros don't have well-defined
behavior.  If I needed such a macro probably I would just
define it myself (and would be confident that it would
work correctly).

In this case I don't need a macro because I would put the gopher
struct at the beginning of the containing struct.  For example:

#include <stdio.h>

typedef struct {
    struct gopher_s go;
    unsigned words;
} WordCounter;


static void
print_word( Gopher go, const char *s, const char *t ){
  WordCounter *context = (void*) go;
  int    n      =  t-s;

    printf( "  word:  %.*s\n", n, s );
    context->words ++;
}


int
main(){
  WordCounter wc = { { print_word }, 0 };
  char  *words = "\tthe quick \"brown fox\" jumps over the lazy dog.";

    words_do( words, &wc.go );
    printf( "\n" );
    printf( " There were %u words found\n", wc.words );
    return  0;
}