Re: Nested conditional compilation

On 20/01/2014, at 01:52, Richard A. O'Keefe <[email protected]> wrote:

> 
> On 20/01/2014, at 12:16 AM, Steve Moyle wrote:
> 
>> Hi, is it possible to perform nested conditional compilation?
> 
> Did you _try_ it?
> 
> When I did in 6.5, seriously weird things happened.
> Perhaps it works in later versions.
> 
> It can always be simulated:
> 
> :- if(G1).
>   B1.
>   :- if(G2).
>      B12.
>   :- else.
>      B1_2.
>   :- end.
> :- else.
>   B_1.
>   :- if(G2).
>      B_12.
>   :- else.
>      B_1_2.
>   :- end.
> :- end.
> 
> ===>
> 
> :- if(G1).
>   B1.
> :- end.
> :- if((G1, G2)).
>   B12.
> :- else.
>   B1_2.
> :- end.
> :- if(\G1).
>   B_1,
> :- end.
> :- if((\G1,G2)).
>   B_12.
> :- else.
>   B_1_2.
> :- end.
> 
> For the record, here's what 6.5.1 did.
> 
> % cat ab.pl
> a :- true.
> 
> b :- fail.
> 
> <EOF>
> % cat abc.pl
> :- if(a).
>   p(a). 
>   :- if(b).
>      p(a+b).
>   :- else.
>      p(a-b).
>   :- end.

You want ":- endif.", not ":- end.".

>   :- else.  
>   p(-a).
>   :- if(b).
>      p(-a+b).
>   :- else.
>      p(-a-b).
>   :- end.   
> :- end.   
> <EOF>
> % swipl
> Welcome to SWI-Prolog (Multi-threaded, 64 bits, Version 6.5.0)
> 
> ?- [ab].
> % ab compiled 0.00 sec, 3 clauses
> true.
> 
> ?- [abc].
> ERROR: /home/cshome/o/ok/abc.pl:7:
>        catch/3: Undefined procedure: end/0
> Warning: /home/cshome/o/ok/abc.pl:7:
>        Goal (directive) failed: user:end
> ERROR: /home/cshome/o/ok/abc.pl:17:
>        Unterminated conditional compilation from abc.pl:12
> % abc compiled 0.01 sec, 1,316 clauses
> true.
> 
> ?- listing(p/1).
> ERROR: [Thread 1]: exception handler failed to define listing/1
> 
> ERROR: [Thread 1]: exception handler failed to define listing/1
> 
>   Call: (6) listing(p/1) ? abort
> % Execution Aborted
> ERROR: load_files/2: No permission to load source `/opt/local/lib/swipl-6.5.0/library/prolog_history.pl' (Non-module file already loaded into module $toplevel; trying to load into prolog_history)
> ERROR: setup_history/0: Undefined procedure: prolog_history:prolog_history/1

Fixing the "end" -> "endif" typo:

$ swipl
% /Users/pmoura/.plrc compiled 0.00 sec, 2 clauses
Welcome to SWI-Prolog (Multi-threaded, 64 bits, Version 7.1.5-3-g73a511b-DIRTY)
Copyright (c) 1990-2013 University of Amsterdam, VU Amsterdam
SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to redistribute it under certain conditions.
Please visit http://www.swi-prolog.org for details.

For help, use ?- help(Topic). or ?- apropos(Word).

?- [ab].
% ab compiled 0.00 sec, 3 clauses
true.

?- [abc].
% abc compiled 0.00 sec, 9 clauses
true.

?- listing(p/1).
p(a).
p(a-b).

true.

Cheers,

Paulo

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Paulo Moura
Logtalk developer

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