Runtime non-failure checker for SWI-Prolog

Many predicates dealing with databases and external systems are non-failure. These predicates have the following properties:

• They should not fail.
• The first solution is the right solution.
• Errors are handled through exceptions.

This library attempts to provide runtime check for these conditions.


API

Use directive rdet/1 to annotate predicates that are supposed to be deterministic:

:- rdet(somepred/arity).

When annotated predicate call fails, an error is thrown:

error(goal_failed(PredicateIndicator), _)

Example

:- use_module(library(rdet)).

:- rdet(insert_sort/2).
:- rdet(i_sort/3).
:- rdet(insert/3).

insert_sort(List, Sorted):-
    i_sort(List, [], Sorted).

i_sort([], Acc, Acc).
i_sort([H|T], Acc, Sorted):-
    insert(H,Acc,NAcc),
    i_sort(T,NAcc,Sorted).

insert(X,[Y|T],[Y|NT]):-
    X>Y,
    insert(X,T,NT).

insert(X,[Y|T],[X,Y|T]):-
    X=<Y.

insert(X,[a],[X]).

Running the sorting procedure will throw an error (the last clause of insert/3 is intentionally made to fail with numbers):

?- insert_sort([2,4,1,3], Sorted).
ERROR: Unhandled exception: Goal insert/3 failed.

How does it work?

The library uses SWI-Prolog built-in predicate wrap_predicate to insert necessary checks.

Previous version of this library was using goal expansion.

Debugging

Enable rdet debug statements (before loading code to be enhanced):

?- debug(rdet).
Warning: rdet: no matching debug topic (yet)
true.

?- [insert].
% rdet: adding goal: user:insert_sort/2
% rdet: adding goal: user:i_sort/3
% rdet: adding goal: user:insert/3
true.

Module named user?

Module named user usually contains the code that is not explicitly put into a module.

Why not a static system?

Good luck building a static analysis system that includes the following:

• Instantiatedness (unbound, ground, partial)
• Type information (list vs. atom, higher order types)
• Module system support
• Supports goal_expansion and other extensions
• Higher order calls (maplist/call/etc)
• Static exceptions
• Different determinism modes: det/semidet/nondet/comitted choice
• Determinism dependence on all previous

And has all of this optional: you can combine your code easily with 3rd party untyped/unmoded libraries.

Installation

To install as a package:

pack_install(rdet).

It requires a recent SWI-Prolog version 8.x or newer.

Running tests

In the package root, insert into swipl:

[tests/tests].
run_tests.

Or if you cloned the repo:

make test

Bug reports/feature requests

Please send bug reports/feature request through the GitHub project page.

License

The MIT license. See the LICENSE file.