From: Salvador Abreu <address@hidden>
To: Dave Sworin <address@hidden>
Cc: address@hidden
Sent: Friday, January 27, 2012 1:47 AM
Subject: Re: Is GNU Prolog interpreter output missing quotes for '<>', '[]', and '{}'?
Hi,
On Jan 27, 2012, at 05:45, Dave Sworin wrote:
> In gprolog 1.3.1 and gprolog 1.4.0 the following
occurs.
>
> A = '[]'.[ENTER KEY PRESSED]
> A = []
>
> The same is true for '{}' and '<>'. However, '()' works as I expected.
>
> If a term includes the atom '[]', the term displays an empty list instead of an atom.
>
> A = f(abc,1.25,'[]').[ENTER KEY PRESSED]
> A = f(abc,1.25,[])
>
> So the term now contains an empty list.
The empty list is, by definition, the atom '[]' (which is the *same thing* as just [], without the quotes).
> This seems so very minor but when I copy GNU Prolog output
> from the interpreter display and paste it back into the interpreter
> for another query, the term is incorrect and the query fails.
>
> I encountered this when writing code which outputs some Prolog source code
> as in a small code generator for a repetitive task.
If you want to write
something that can be read back in (or pasted into the top-level) you want to use writeq/1 or write_canonical/1. Typically you would use
...make term X...
writeq(X), write(.), nl,
...keep going...
whatever is written may (normally) get read back in (or copy-pasted).
another possibility is to use format/2, as in:
...make X...
format("~q.~n", [X]),
...
> Is this a bug???
No. :-)
regards,
--
Salvador Abreu -- http://www.di.uevora.pt/~spa/
Departamento de Informatica
Universidade de Evora - PORTUGAL