[m-dev.] Minimal streams diff

[Fergus Henderson]

A couple of quick comments:
	- what is the rationale for this change?
	- how does this differ from Peter Ross's stream stuff
	  (which I think lives in extras/stream)?

On 02-Oct-2002, Michael Day <mikeday at yeslogic.com> wrote:
> 
> Seeing as how Fergus has just announced a feature freeze, it seems like a
> good time to post a minimal streams diff for the day after the next
> release staggers out the door.
> 
> I've tried to keep it to the minimum level of changes necessary to
> introduce stream type classes into the standard library, so it doesn't
> include putback streams or line number counting or anything like that. 
> 
> Interestingly enough, I ended up implementing socket streams on top of the
> posix code for the ICFP contest and they worked pretty well, but the lack
> of integration with regular io streams and the incredible irritation of
> having to manipulate separate io__result and stream__result types is a
> killer for any real usage.
> 
> Anyway, anyone not busy frantically squashing bugs for the release, please 
> feel free to criticise the diff below.
> 
> Michael
> 
> --- ../mercury-compiler-rotd-2002-09-07/library/io.m	Thu Jul 25 02:05:11 2002
> +++ io.m	Wed Oct  2 11:47:33 2002
> @@ -112,6 +112,43 @@
>  	;	end
>  	.
>  
> +% Type classes
> +
> +:- typeclass input(S) where
> +    [
> +	pred input_stream_name(S, string, io, io),
> +	mode input_stream_name(in, out, di, uo) is det,
> +%		Retrieves the human-readable name associated with the
> +%		specified input stream.
> +%		For file streams, this is the filename.
> +%		For stdin this is the string "<standard input>".
> +
> +	pred read_char(S, io__result(char), io, io),
> +	mode read_char(in, out, di, uo) is det
> +%		Reads a character from specified stream.
> +    ].
> +
> +:- instance input(input_stream).
> +
> +:- typeclass output(S) where
> +    [
> +	pred output_stream_name(S, string, io, io),
> +	mode output_stream_name(in, out, di, uo) is det,
> +%		Retrieves the human-readable name associated with the
> +%		specified stream.
> +%		For file streams, this is the filename.
> +%		For stdout this is the string "<standard output>".
> +%		For stderr this is the string "<standard error>".
> +
> +	pred write_char(S, char, io, io),
> +	mode write_char(in, in, di, uo) is det
> +%		Writes a character to the specified output stream.
> +    ].

Why not have the stream_name predicate in a base class inherited from
both input and output?

Wouldn't it be better to name the classes input_stream and output_stream?

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  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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