Re: Users-prolog Digest, Vol 134, Issue 1

[Duncan Patton a Campbell]

On Tue, 14 Oct 2014 12:00:52 -0400
address@hidden wrote:

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> Today's Topics:
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>    1. Style guide / optimisation... (emacstheviking)
>    2. Re: Style guide / optimisation... (Daniel Diaz)
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> Message: 1
> Date: Mon, 13 Oct 2014 23:42:33 +0100
> From: emacstheviking <address@hidden>
> To: "address@hidden" <address@hidden>
> Subject: Style guide / optimisation...
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> 
> Hi,
> 
> I just knocked these out to read a file into memory for DCG practice over
> files. I know they might not be the best they can which is why I am asking
> for how to make it more efficient...
> 
> file_codes(From, Out) :-
> open(From, read, S),
> file_read_buf(S, [], get_code, -1, Out),
> close(S).
> 
> file_chars(From, Out) :-
> open(From, read, S),
> file_read_buf(S, [], get_char, end_of_file, Out),
> close(S).
> 
> file_read_buf(S, Acc, Fetcher, Eof, Out) :-
> Reader =.. [Fetcher, S, Chr],
> call(Reader),
> ( Chr == Eof -> reverse(Acc, Out) ; file_read_buf(S, [Chr|Acc], Fetcher,
> Eof, Out)).
> 
> I wanted to avoid using =.. every time I read another bit of the file; it
> just feels like it should be outside the loop, I tried this but it didn't
> do what I expected:
> 
>     file_read_buf(S, [], get_code(S, _Chr), -1, Out)
> 
> So, how can I make this more efficient and prolog-gy?
This is what I use.  If you improve on it, let me know.

file_str(Fname,Fstr):-
        nonvar(Fstr),
        atom(Fname),!,
        file_outs(Fname,Fstr).
file_str(FnameS,Fstr):-
        nonvar(FnameS),
        nonvar(Fstr),
        atom_codes(Fname,FnameS),!,
        file_outs(Fname,Fstr).
file_str(Fname,Fstr):-
        var(Fstr),
        atom(Fname),!,
        file_ins(Fname,Fstr).
file_str(FnameS,Fstr):-
        var(Fstr),
        nonvar(FnameS),
        atom_codes(Fname,FnameS),!,
        file_ins(Fname,Fstr).

file_outs(Fname,Fstr):-
        open(Fname, 'write', Strout),
        set_stream_type(Strout,binary),!,
        writebytes(Strout,Fstr),close(Strout),!.


file_ins(Fname,Fstr):-
        open(Fname, 'read', Strin),
        set_stream_type(Strin,binary),
        readbytes(Strin,Fstr),!,close(Strin),!.

readbytes(Strin,[]):- at_end_of_stream(Strin),!.
readbytes(Strin,[Chr|ReadlS]):-
        get_byte(Strin,Chr),!,
        readbytes(Strin,ReadlS).
%readbytes(Strin,[[]|ReadlS]):-!, readbytes(Strin,ReadlS).

writebytes(_,[]):- !.
writebytes(Strout,[Chr|ReadlS]):-
        put_byte(Strout,Chr),!,
        writebytes(Strout,ReadlS).

Also

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I never seem to be able to get these attachments as this
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is what lists.gnu.org always returns.

Dhu

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> End of Users-prolog Digest, Vol 134, Issue 1
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