Re: Difficulties with \

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.

> ?- 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.

> ?- 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.