[Xsb-development] [ xsb-Bugs-222707 ] Interaction of tabling with input/output predicates

[<no...@so...>]

Bugs item #222707, was opened at 2000-11-17 10:38
You can respond by visiting: 
http://sourceforge.net/tracker/?func=detail&atid=101176&aid=222707&group_id=1176

Category: Tabling/Negation
Group: wrong answer
Status: Open
Resolution: None
Priority: 5
Submitted By: Carlos Viegas Damásio (carlosdamasio)
Assigned to: Nobody/Anonymous (nobody)
Summary: Interaction of tabling with input/output predicates

Initial Comment:
Dear All,

I have some doubts regarding the interaction of tabling and predicates with side-effects.
I've got unexpected results (at least for me...).

I wanted to fill up a table with the contents of a file, indexed by its position.

I've tried the following code:

	:- import file_open/3 from file_io.
	:- import file_close/1 from file_io.
	:- import file_getbuf/4 from file_io.
	:- import file_seek/4 from file_io.

	:- table stream/3.

	open_stream( FileName, FileDes ) :-
		file_open( FileName, 0, FileDes ).

	close_stream( FileDes ) :-
		file_close( FileDes ).

	stream( FileDes, N, Byte ) :-
	%	file_seek( FileDes, N, 0, _ ),
		file_getbuf( FileDes, 1, Byte, Read ), Read = 1.

Here is an example:

	[configuration loaded]
	[sysinitrc loaded]
	[packaging loaded]

	XSB Version 2.0 (Gouden Carolus) of June 27, 1999
	[x86-pc-windows; mode: optimal; engine: chat; scheduling: batched]
	| ?- [stream0].
	[Compiling .\stream0]
	[stream0 compiled, cpu time used: 0.9300 seconds]
	[stream0 loaded]

	yes
	| ?- open_stream('lixo.P',F).

	F = 3;

	no
	| ?- stream(3,0,N).

	N = c;

	no
	| ?- stream(3,1,N).

	N = o;

	no
	| ?- stream(3,2,N).

	N = n;

	no
	| ?- stream(3,0,N).

	N = n;

	no

The first result has been recomputed!!! (If I put the file_seek everything works fine, but XSB executes again the same code).

	| ?- close_stream(3).

	yes
	| ?- stream(3,0,N).

	N = n;

	no
	| ?- stream(3,1,N).

	N = n;

	no
	| ?- stream(3,2,N).

	N = n;

	no

Then, instead of performing file input I tried with read predicate:

	:- table stream/3.

	open_stream( FileName, 0 ) :-
		see( FileName ).

	close_stream( 0 ) :-
		seen.

	stream( F, N, Byte ) :-
		read( Byte ).

	| ?- open_stream('lixo.P',F).
	
	F = 0;

	no

	| ?- stream(0,0,N).

	N = conn(inv4,i,inv1);

	no
	| ?- stream(0,1,N).

	N = conn(and2,i1,inv1);

	no
	| ?- stream(0,2,N).

	N = conn(and3,i2,inv1);

	no
	| ?- stream(0,0,N).

	N = conn(inv4,i,inv1);

	no
	| ?- stream(0,2,N).

	N = conn(and3,i2,inv1);

	no

Now, it works as I expected! But if I use get0 instead of read the same problem occurs!
I also tried a version with assert and retract, and it also works.

	:- table stream/3.

	:- dynamic ctr/1.

	open_stream( FileName, 0 ) :-
		assert( ctr(0) ).

	close_stream( 0 ) :-
		retract( ctr(_) ).

	stream( 0, N, Byte ) :-
		retract(ctr(Byte)),
		NewByte is Byte + 1,
		assert( ctr(NewByte) ).


	| ?- open_stream('lixo.P',F).

	F = 0;

	no
	| ?- stream(0,0,N).

	N = 0;

	no
	| ?- stream(0,1,N).

	N = 1;

	no
	| ?- stream(0,2,N).

	N = 2;

	no
	| ?- stream(0,0,N).

	N = 0;

	| ?- stream(0,2,N).

	N = 2;

	no
	| ?- stream(0,1,N).

	N = 1;

	no
	| ?- stream(0,3,N).

	N = 3;

	no

----------------------------------------------------------------------

>Comment By: Luis Castro (lfcastro)
Date: 2001-07-12 10:50

Message:
Logged In: YES 
user_id=6694

I could not reproduce your error in the current system. Does
it still happen to you?

----------------------------------------------------------------------

You can respond by visiting: 
http://sourceforge.net/tracker/?func=detail&atid=101176&aid=222707&group_id=1176