From jan@swi.psy.uva.nl  Wed Dec 22 11:40:01 1999
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Date: Wed, 22 Dec 1999 11:40:12 +0100
Message-Id: <199912221040.LAA13803@gollem.swi.psy.uva.nl>
From: Jan Wielemaker <jan@swi.psy.uva.nl>
Subject: Re: tell/1 , append/1 , open/4  ??????
To: dazy@cnam.fr, prolog@swi.psy.uva.nl
In-Reply-To: jfd's message of Wed, 22 Dec 1999 11:27:56 +0500
Phone: +31 - 20 - 525 6121

> Hi,
> in a course for foundation of programming, we have written a
> demonstration editor...
> So that the student can show their demonstrations, i have written a
> couple of clauses which copy in a file (trace.dem') the screen session : 
> %predicats de service
> 
> dw(X)
> 		:-
> 		tell('trace.dem'),
> 		write(X),
> 		tell(user),
> 		write(X).
> 
> dnl
> 		:-
> 		tell('trace.dem'),
> 		nl,
> 		tell(user),
> 		nl.
> 
> 'DR'(X) 
> 		:-
> 		read(X),
> 		tell('trace.dem') , 
> 		write(X) , nl , tell(user) , nl.
> 
> 
> This work well with simple Prolog (OPEN on macOS) and not
> with SWI 3.2.8
> what wrong in this picture ?
> help , help

You never do a told, nor a flush, so your output is somewhere
pending in the Prolog I/O buffers.  See help(told).

	Regards --- Jan