Typo is a type and syntax checker reporting tool using metainterpretation.
The metainterpertation critic (metainterpret/2 or metainterpret/3)
gives us information as to causes of failure for a restricted subset
of prolog in which ; is interpreted as exclusive disjunction.
From the error tree, which is a kind of recording of the failed SLD tree, we can then determine a likely target for "most interesting failure", for instance by looking for those resolution paths of greatest depth.
This library is useful for creating either an ad-hoc type-checker which verifies syntax of a term (well-formedness conditions etc.) or for creating a full fledged type checker.
In order to invoke the metainterpretation critic, simply write down
some syntax checking predicates and you can use metainterpret/3 to
invoke them. For instance, given the following programme:
isa_integer_list([]).
isa_integer_list([H|T]) :-
isa_integer(H),
isa_integer_list(T).
-? metainterpret(user, isa_integer_list([1,2,3]), ME).
ME = none.
The metainterpreter will bind ME to a maybe(error) type:
:- type maybe(T) ---> none ; just(T).
resulting in none if there is no error, and just(Error) if there is
one (or many). The Error type is:
:- type error ---> error_leaf(any,atom) ; error_branch(any,atom,list(error)).
We can extract a likely cause of the failure by looking at the deepest
branch of the error tree, which can be extracted with deepest/2 which extracts a stack
of errors and it can be printed with write_stack/1 as follows:
:- metainterpret(user, isa_integer_list([1,2,x]), just(Error)), deepest(Error,Stack), write_stack(Stack).
x is not an integer
Left conjuct fails: isa_integer(x)
No successful clause for predicate isa_int_list([x])
Right conjuct fails: isa_int_list([ x ])
No successful clause for predicate isa_int_list([2,x])
Right conjuct fails: isa_int_list([ 2, x ])
No successful clause for predicate isa_int_list([1,2,x])
...
Author: Gavin Mendel-Gleason
Copyright: Datachemist Ltd.
Licence: Apache License 2.0