add documentation

src/lib/ffi.pl

@@ -72,6 +72,21 @@ And a new window should pop up!
 foreign_struct(Name, Elements) :-
     '$define_foreign_struct'(Name, Elements).
 
+
+%% use_foreign_module(+LibName, +Predicates)
+%
+% - LibName the path to the shared library to load/bind
+% - Predicates list of function definitions
+%
+%   Each function definition is a functor of arity 2.
+%   The functor name is the name of the function to bind,
+%   the first argument is the list of arguments of the function,
+%   the second argument is the return type of the function.
+%
+%   This will define a predicate in the ffi module with the defined name,
+%   for void and bool return type functions the arity will match the length of the arguments list,
+%   for other return types there will be an additional out parameter.
+%
 use_foreign_module(LibName, Predicates) :-
     '$load_foreign_lib'(LibName, Predicates),
     maplist(assert_predicate, Predicates).
@@ -112,19 +127,34 @@ assert_predicate(PredicateDefinition) :-
     Predicate = (Head:-Body),
     assertz(ffi:Predicate).
 
-
+%% allocate(+Allocator, +Type, +Args, -Ptr)
+%
+% Using the Allocator allocate Type initialized with Args and 
+% unify Ptr with a pointer to that allocation.
+%
 allocate(Allocator, Type, Args, Ptr) :-
     must_be(var, Ptr),
     must_be(atom, Type),
     must_be(atom, Allocator),
     '$ffi_allocate'(Allocator, Type, Args, Ptr).
 
+
+%% read_ptr(+Type, +Ptr, -Value)
+%
+% Read a value of Type from the pointer Ptr and unify the read value with Value
+%
+% For type cstr take read a nul-terminated utf-8 string starting at Ptr.
+%
 read_ptr(Type, Ptr, Value) :-
     must_be(var, Value),
     must_be(atom, Type),
     must_be(integer, Ptr),
     '$ffi_read_ptr'(Type, Ptr, Value).
 
+%% deallocate(+Allocator, +Type, +Ptr)
+%
+% Deallocate the allocation at Ptr of Type allocated with Allocator
+%
 deallocate(Allocator, Type, Ptr) :-
     must_be(atom, Allocator),
     must_be(integer, Ptr),
@@ -132,6 +162,10 @@ deallocate(Allocator, Type, Ptr) :-
 
 :- dynamic(is_array_type_defined/1).
 
+%% array_type(+ElemType, +Len, -ArrayType)
+%
+% unify the ffi type for an array of lenth Len with element type ElemType with ArrayType
+%
 array_type(ElemType, Len, ArrayType) :-
     (Len =< 0 -> domain_error(greater_than_zero, Len, array_type/3); true),
     phrase(format_("$[~a;~d]", [ElemType, Len]), ArrayTypeName),
@@ -143,6 +177,14 @@ array_type(ElemType, Len, ArrayType) :-
         assertz(is_array_type_defined(ArrayType))
     ).
 
+%% with_locals(+Locals, :Goal)
+%
+%  Allocate the Locals, evaluate the Goal and deallocate the Locals.
+%  The Locals will also be cleandup when Goal fails or throws an error.
+%
+%  Locals is a list of local variable definitions let(-Ptr, +Type, +Args).
+%  Ptr will be unified with the pointer to the local of Type initialized with Args.
+%
 with_locals(Locals, Goal) :-
     verify_locals(Locals),
     setup_call_cleanup(