:- module(testmodule, []).
:- use_module(library(lists)).
:- use_module(library(math)).                     % require foreign code

/*
Extern declaration for builtins used by our C code
*/

:- extern(writeq(+string, +term)).
:- extern(flush_output(+string)).
:- extern(nl(+string)).

/* Just an example of some other code callable from C
*/

:- extern(do_something(+string, -string)).
do_something(Indata, Result) :-
   format(user_error, 'Prolog: do_something(~w, ~w)~n', [Indata, Result]),flush_output(user_error),
   name(Indata, L),
   reverse(L, R),
   name(Result, R).


:- extern(do_something_illegal(+integer, -integer)).
do_something_illegal(Indata, Result) :-
   format(user_error, 'Prolog: do_something_illegal(~w, ~w)~n', [Indata, Result]),flush_output(user_error),
   Result is integer(1000/Indata).


:- extern(do_something_nondet(-double)).
do_something_nondet(Result) :-
   format(user_error, 'Prolog: do_something_nondet clause 1~n', []),flush_output(user_error),
   sqrt(42,Result).
do_something_nondet(Result) :- 
   format(user_error, 'Prolog: do_something_nondet clause 2~n', []),flush_output(user_error),
   Result = 2.2.
do_something_nondet(Result) :-
   format(user_error, 'Prolog: do_something_nondet clause 3~n', []),flush_output(user_error),
   Result = 3.3.


%% specify that the predicate callback_pred(X,Y) should call the C
%% function callback_fun(X) and set Y to the (integer) result.
foreign(callback_fun, c, callback_pred(+integer, [-integer])).

foreign_file('myforeign.o', [callback_fun]).

% :- load_foreign_executable(myforeign), % myforeign.so must be available at run-time
%    abolish(foreign/3), abolish(foreign_file/2).

:- load_foreign_files(['myforeign.o'], []), % myforeign.o must be available at qpc compile time
   abolish(foreign/3), abolish(foreign_file/2).


:- extern(do_something_callback(+integer, -integer)).
do_something_callback(Indata, Result) :-
   format(user_error, 'In Prolog do_something_callback(~w, ~w).~n', [Indata,Result]),flush_output(user_error),
   X1 is Indata+1,
   format(user_error, 'Prolog: calling callback_pred(~w, ~w).~n', [X1,X2]),flush_output(user_error),
   callback_pred(X1, X2),       % call into C
   format(user_error, 'Prolog: called callback_pred(~w, ~w).~n', [X1,X2]),flush_output(user_error),
   Result is X2+1.