Re: Style guide / optimisation...

Hi

You are right =.. is not very efficient. You can use call/2-N to
avoid this

http://www.gprolog.org/manual/html_node/gprolog042.html#sec194

Also the reverse is time and space consuming. This is strange
because you use an accumulator: this is generally used to avoid
append or reverse. In fact the accumulator is not needed and
avoids the use of reverse.

Here is the resulting version:

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, Fetcher, Eof, Out) :-

call(Fetcher, S, Chr),

( Chr \== Eof ->

Out = [Chr|Out1],

file_read_buf(S, Fetcher, Eof, Out1)

;

Out = []

).

Daniel

Le 14/10/2014 00:42, emacstheviking a écrit :

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?

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