[m-rev.] for review: improve string__replace and string__replace_all

[Peter Ross]

On Mon, Dec 06, 2004 at 11:40:20AM +1100, Ralph Becket wrote:
> Peter Ross, Sunday,  5 December 2004:
> > Index: library/string.m
> > ===================================================================
> > RCS file: /home/mercury1/repository/mercury/library/string.m,v
> > retrieving revision 1.221
> > diff -u -r1.221 string.m
> > --- library/string.m	10 Nov 2004 07:12:38 -0000	1.221
> > +++ library/string.m	5 Dec 2004 16:26:38 -0000
> > @@ -609,7 +609,9 @@
> >  
> >  string__replace_all(Str, Pat, Subst, Result) :-
> >  	( Pat = "" ->
> > -		copy(Str, Result)
> > +		F = (func(C, L) = [char_to_string(C) ++ Subst | L]),
> > +		Foldl = string__foldl(F, Str, []),
> > +		Result = append_list([Subst | list__reverse(Foldl)])
> >  	;
> >  		PatLength = string__length(Pat),
> >  		ReversedChunks = replace_all(Str, Pat, Subst, PatLength, 0, []),
> 
> Just as a minor efficiency hack, I'd move the char_to_string(C) computation 
> out of the lambda - loop invariant hoisting isn't turned on until -O5 or
> 6 IIRC and even then it might not hoist it.
> 
I would love to move it out, but then the program wouldn't be correct.
As the value for C supplied is for each character in the string, so it
is always changing.

Pete
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