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
pengines:prepare_module(Module, myapp, _Options) :-
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:
- Emit Term as <span class=writeln>Term<br></span>.
- Emit a <br/> to the pengine.
- No-op. Pengines do not use output buffering (maybe they should
- pengine_write_term(+Term, +Options)
- Writes term as <span class=Class>Term</span>. In addition to the
options of write_term/2, these options are processed:
- Specifies the class of the element. Default is
- 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 <br/> 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.
- message_lines_to_html(+MessageLines, +Classes, -HTMLString) is det
- Helper that translates the Lines argument from user:message_hook/3
into an HTML string. The HTML is a <pre> object with the class
'prolog-message' and the given Classes.
- 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.
|Vars||- is a list of variable names or |
 if Term is a
- Hook into help/1 to render the help output in the SWISH console.
- True when Head describes the head of a (system) IO predicate
that is redefined by the HTML binding.
- Redefine the built-in predicates for IO to send HTML messages
The following predicates are exported, but not or incorrectly documented.
- pengine_io_goal_expansion(Arg1, Arg2)
- pengine_read_line_to_codes(Arg1, Arg2)
- pengine_read_line_to_string(Arg1, Arg2)