pengines_io.pl -- Provide Prolog I/O for HTML clients

This module redefines some of the standard Prolog I/O predicates to behave transparently for HTML clients. It provides two ways to redefine the standard predicates: using goal_expansion/2 and by redefining the system predicates using redefine_system_predicate/1. The latter is the preferred route because it gives a more predictable trace to the user and works regardless of the use of other expansion and meta-calling.

Redefining works by redefining the system predicates in the context of the pengine's module. This is configured using the following code snippet.

:- pengine_application(myapp).
:- use_module(myapp:library(pengines_io)).
pengines:prepare_module(Module, myapp, _Options) :-
      pengines_io:pengine_bind_io_to_html(Module).

Using goal_expansion/2 works by rewriting the corresponding goals using goal_expansion/2 and use the new definition to re-route I/O via pengine_input/2 and pengine_output/1. A pengine application is prepared for using this module with the following code:

:- pengine_application(myapp).
:- use_module(myapp:library(pengines_io)).
myapp:goal_expansion(In,Out) :-
      pengine_io_goal_expansion(In, Out).

pengine_writeln(+Term)

Emit Term as Term .

pengine_nl

Emit a to the pengine.

pengine_flush_output

No-op. Pengines do not use output buffering (maybe they should though).

pengine_write_term(+Term, +Options)

Writes term as Term. In addition to the options of write_term/2, these options are processed:

class(+Class): Specifies the class of the element. Default is write.

pengine_write(+Term) is det

pengine_writeq(+Term) is det

pengine_display(+Term) is det

pengine_print(+Term) is det

pengine_write_canonical(+Term) is det

Redirect the corresponding Prolog output predicates.

pengine_format(+Format) is det

pengine_format(+Format, +Args) is det

As format/1,2. Emits a series of strings with for each newline encountered in the string.

To be done: - : handle ~w, ~q, etc using term//2. How can we do that??

pengine_listing is det

pengine_listing(+Spec) is det

List the content of the current pengine or a specified predicate in the pengine.

user:message_hook(+Term, +Kind, +Lines) is semidet[multifile]

Send output from print_message/2 to the pengine. Messages are embedded in a <pre class=msg-Kind></pre> environment.

binding_term(+Term, +Vars, +WriteOptions)// is semidet[multifile]

Hook to render a Prolog result term as HTML. This hook is called for each non-variable binding, passing the binding value as Term, the names of the variables as Vars and a list of options for write_term/3. If the hook fails, term//2 is called.

Arguments:

Vars - is a list of variable names or [] if Term is a residual goal.

pengine_io_predicate(?Head)