Re: Difficulties with \

On 26/10/2013 00:57, Pierpaolo Bernardi wrote:
> On Sat, Oct 26, 2013 at 12:14 AM, joel<[email protected]>  wrote:
>> Hello all
>>
>> How can I create atom \sin ?
> If you want the atom whose name is composed by the four characters \,
> s, i, n, then the literal syntax is '\\sin'
>
>> I get for example
>>
>> ?- writef('%n%w', [92,sin]).
>> \sin
>> true.
> You just wrote the characters.
Yes, I understood that this morning, I think I was a little bit tired 
this night.
>> ?- with_output_to(atom(A), writef('%n%w', [92,sin])).
>> A = '\\sin'.
> that's the atom you want. You can check with writeln:
>
> 16 ?- writeln('\\sin').
> \sin
> true.
>
> or with atom_chars:
>
> 18 ?- atom_chars('\\sin',C).
> C = [\, s, i, n].
>
>> Idem :
>>
>> ?- A= \sin.
>> A = \sin.
> This is not an atom:
>
> 11 ?- atom(\sin).
> false.
> 12 ?- write_canonical(\sin).
> \(sin)
> true.
Useful tip, I didn't think of that.

> ?- A= \sin, atomic_list_concat([A, '(', 8, ')'], L).
> ERROR: atomic_list_concat/2: Type error: `text' expected, found `\sin'
> right. since A is not an atom.
>
>> ?- A= '\sin', atomic_list_concat([A, '(', 8, ')'], L).
>> A = ' in',
>> L = ' in(8)'.
> now A is an atom, but \s in a quoted atom name is an escape sequence
> for the space character.
>
>> ?- A= '\\sin', atomic_list_concat([A, '(', 8, ')'], L).
>> A = '\\sin',
>> L = '\\sin(8)'.
>>
>> Is it a bug ?
> No. It's all working fine.  Read section '2.15.1.2 Character Escape
> Syntax' in the manual for the full details.
>
> P.
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Thank you very much, I get it now !

Cheers

Joël