transformer

Tools for program transformation in prolog.

Optimiser

The optimiser is intended to give a suite of optimisations that can be performed on a file wide, or per-predicate basis.

Currently the only optimisation method deployed is a search for clause-overlap which inserts cuts when we can prove that subsequent clauses are unreachable.

To start the optimiser on a predicate:

:- use_module(library(transformer)).

:- optimise(p/3).
p(x,y,z) :- q.
p(x,w,z) :- r.
p(x,y,a) :- s.

or run it on the whole file:

:- use_module(library(transformer)).
:- optimise_all.

or go wild and let it run on everything!

:- use_module(library(transformer)).
:- optimise_everything.

Options

To set options you can run:

:- set_optimise_options(Options)

Currently the only options are

• equality_cut(Boolean) : Boolean = true for placing cuts when clauses are disjoint
• log_stream(Stream) for reporting information about transformations.

TODO

• A "guard" optimiser which does a search for all predicates at the beginning of a clause which are in a guard language (integer,string,atom,var,nonvar,ground etc.) and places a cut when subsequent clauses are unreachable. Most of the code is already written for this.
• Negative information propagation. Cuts in previous clauses tell us that in order to have cascaded, something before the cut must have been false. i.e

p(X) :-
  nonvar(X),
  int(X),
  !,
  G.
p(X) :-
  H.

  % implies that
  \+ (nonvar(X),
      int(X)) in H.