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

[emacstheviking]

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.

Thanks.