Re: C interface confusion about char codes, lists and atoms...

Le 03/07/2013 18:30, emacstheviking a
écrit :

Can somebody point me to to the docs where it says
"single character atoms are characters" please....

You are right, from the Prolog programmer point of view, a character
is an atom of length 1.

Unfortunately the gprolog doc does not define the syntax of Prolog
terms since gprolog conforms to the ISO standard for Prolog (ok I
should add it).

Lower case letters can be written unquoted (e.g. a, b, ...) orther
chars need to be quoted (e.g. '#', 'A', ...).

Daniel

I seem to have missed something basic. I will also
read LPN, C&M and Art of Prolog tonight and make sure I take
it in that atoms are also characters.

Dammit.

:(

On 3 July 2013 16:26, Daniel Diaz <[email protected] >
wrote:

Le 03/07/2013 16:44, emacstheviking a écrit :

Hi,

I have been experimenting with the foreign
interface and managed to confuse myself.

Given this foreign declaration:

%% :- foreign( foo( +string ), [fct_name( foo
)]). %% +string => atom at call site

%% :- foreign( foo( +codes ), [fct_name( foo )]).

:- foreign( foo( +codes ), [fct_name( foo )]).

and this implementation:

// +string :: atom ==> char*,
works

// +codes :: character-code list ==> char*,
works as foo("Hello").

// +chars :: character list ==>
char*, fails on call foo("HI"), foo([64,65]).
Why?

PlBool

foo(char* s)

{

printf("FOO: ==> %s\n", s);

return PL_TRUE;

}

My problem is that when I use "+chars" I can't then
say:

foo("Hello")

as I get a type_error so please can anybody explain
to me what "character list" is and how it looks in a
command line session? The flag that controls the
interpretation of double-quoted strings is at its
default value as I have not altered it but I am aware
of its existence and the fact that "" is syntactic
sugaring of lists of codes.

Hi,

+atom means you pass an atom (e.g. abc) and you get the
internal reference of the atom in C (which is an integer)

+chars means you pass a list of characters (e.g. [a,b,c])
and you get a NULL terminated string in C, ie. a char *
(e.g. "abc")

+code means you pass a list of char codes (e.g. [97,98,99]
which is the same a "abc" in Prolog) an dyou get the same
char * as above.

See http://gprolog.univ-paris1.fr/manual/html_node/gprolog068.html

Daniel

Thanks.

--

Ce message a été vérifié par MailScanner pour des virus ou
des polluriels et rien de suspect n'a été trouvé.

_______________________________________________
Users-prolog mailing list
[email protected]
https://lists.gnu.org/mailman/listinfo/users-prolog

--

Ce message a été vérifié par
MailScanner
pour des virus ou des polluriels et rien de
suspect n'a été trouvé.

--

Ce message a été vérifié par
MailScanner
pour des virus ou des polluriels et rien de
suspect n'a été trouvé.

--

Ce message a été vérifié par
MailScanner
pour des virus ou des polluriels et rien de
suspect n'a été trouvé.

_______________________________________________
Users-prolog mailing list
[email protected]
https://lists.gnu.org/mailman/listinfo/users-prolog