terms.pl -- Term manipulation

Compatibility library for term manipulation predicates. Most predicates in this library are provided as SWI-Prolog built-ins.

Compatibility: - YAP, SICStus, Quintus. Not all versions of this library define exactly the same set of predicates, but defined predicates are compatible.

term_size(@Term, -Size) is det

True if Size is the size in cells occupied by Term on the global (term) stack. A cell is 4 bytes on 32-bit machines and 8 bytes on 64-bit machines. The calculation does take sharing into account. For example:

?- A = a(1,2,3), term_size(A,S).
S = 4.
?- A = a(1,2,3), term_size(a(A,A),S).
S = 7.
?- term_size(a(a(1,2,3), a(1,2,3)), S).
S = 11.

Note that small objects such as atoms and small integers have a size 0. Space is allocated for floats, large integers, strings and compound terms.

variant(@Term1, @Term2) is semidet

Same as SWI-Prolog Term1 =@= Term2.

subsumes_chk(@Generic, @Specific)

True if Generic can be made equivalent to Specific without changing Specific.

deprecated: - Replace by subsumes_term/2.

subsumes(+Generic, @Specific)

True if Generic is unified to Specific without changing Specific.

deprecated: - It turns out that calls to this predicate almost always should have used subsumes_term/2. Also the name is misleading. In case this is really needed, one is adviced to follow subsumes_term/2 with an explicit unification.

term_subsumer(+Special1, +Special2, -General) is det

General is the most specific term that is a generalisation of Special1 and Special2. The implementation can handle cyclic terms.

author: - Inspired by LOGIC.PRO by Stephen Muggleton
Compatibility: - SICStus

term_factorized(+Term, -Skeleton, -Substiution)

Is true when Skeleton is Term where all subterms that appear multiple times are replaced by a variable and Substitution is a list of Var=Value that provides the subterm at the location Var. I.e., After unifying all substitutions in Substiutions, Term == Skeleton. Term may be cyclic. For example:

?- X = a(X), term_factorized(b(X,X), Y, S).
Y = b(_G255, _G255),
S = [_G255=a(_G255)].

mapargs(:Goal, ?Term1, ?Term2)

Term1 and Term2 have the same functor (name/arity) and for each matching pair of arguments call(Goal, A1, A2) is true.

mapsubterms(:Goal, +Term1, -Term2) is det

mapsubterms_var(:Goal, +Term1, -Term2) is det

Recursively map sub terms of Term1 into subterms of Term2 for every pair for which call(Goal, ST1, ST2) succeeds. Procedurably, the mapping for each (sub) term pair T1/T2 is defined as:

If T1 is a variable
- mapsubterms/3 unifies T2 with T1.
- mapsubterms_var/3 treats variables as other terms.
If call(Goal, T1, T2) succeeds we are done. Note that the mapping does not continue in T2. If this is desired, Goal must call mapsubterms/3 explicitly as part of its conversion.
If T1 is a dict, map all values, i.e., the tag and keys are left untouched.
If T1 is a list, map all elements, i.e., the list structure is left untouched.
If T1 is a compound, use same_functor/3 to instantiate T2 and recurse over the term arguments left to right.
Otherwise T2 is unified with T1.

Both predicates are implemented using foldsubterms/5.

foldsubterms(:Goal3, +Term1, +State0, -State) is semidet

foldsubterms(:Goal4, +Term1, ?Term2, +State0, -State) is semidet

The predicate foldsubterms/5 calls

call(Goal4, SubTerm1, SubTerm2,
StateIn, StateOut)

for each subterm, including variables, in Term1. If this call fails, StateIn and StateOut are the same. This predicate may be used to map subterms in a term while collecting state about the mapped subterms. The foldsubterms/4 variant does not map the term.

same_functor(?Term1, ?Term2) is semidet

same_functor(?Term1, ?Term2, -Arity) is semidet

same_functor(?Term1, ?Term2, ?Name, ?Arity) is semidet

True when Term1 and Term2 are terms that have the same functor (Name/Arity). The arguments must be sufficiently instantiated, which means either Term1 or Term2 must be bound or both Name and Arity must be bound.

If Arity is 0, Term1 and Term2 are unified with Name for compatibility.

Compatibility: - SICStus

Undocumented predicates

The following predicates are exported, but not or incorrectly documented.

same_functor(Arg1, Arg2, Arg3, Arg4)
term_hash(Arg1, Arg2, Arg3, Arg4)
cyclic_term(Arg1)
term_variables(Arg1, Arg2, Arg3)
same_functor(Arg1, Arg2, Arg3)
term_hash(Arg1, Arg2)
foldsubterms(Arg1, Arg2, Arg3, Arg4, Arg5)
mapsubterms_var(Arg1, Arg2, Arg3)