[m-dev.] for review: destructive changes to string.m

[Fergus Henderson]

On 10-Nov-2000, Michael Day <mikeday at corplink.com.au> wrote:
> 
> Allows checking string length without losing uniqueness and adds
> predicates to allow changing arbitrary characters in a string, handy for
> implementation of string streams.
> 
> library/string.m:
> 	Added a new mode definition to string__length using unique input
> 	so as not to destroy uniqueness when checking string length.
> 
> 	Added three new predicates, string__set, set_det and unsafe_set
> 	that allow changing arbitrary characters in a string. These function
> 	similarly to the corresponding index, index_det and unsafe_index
> 	predicates. (Is set an appropriate name? Overloading index/3 with
> 	index/4 is presumably a bad idea).

I suggest using `set_char' (and `set_char_det', `unsafe_set_char').

It might be better to make those functions rather than predicates.

>  /*
> +:- pred string__set(char, int, string, string).
> +:- mode string__set(in, in, in, out) is semidet.
> +*/
> +:- pragma c_code(string__set(Ch::in, Index::in, Str0::in, Str::out),
> +		[will_not_call_mercury, thread_safe], "
> +	size_t len = strlen(Str0);
> +	if ((MR_Word) Index >= len) {

s/MR_Word/MR_Unsigned/

(MR_Word should be treated as an opaque type,
if you want an unsigned type use MR_Unsigned.)

> +:- pragma c_code(string__set(Ch::in, Index::in, Str0::di, Str::uo),
> +		[will_not_call_mercury, thread_safe], "
> +	if ((MR_Word) Index >= strlen(Str0)) {

Likewise.

>  :- func string__length(string) = int.
> +:- mode string__length(in) = uo is det.

You should add the `(ui) = uo' mode too.

Apart from that, this change looks fine.

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
                                    |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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