terms.pl -- SICStus 4-compatible library(terms).

To be done

- This library is incomplete. As of SICStus 4.6.0, the following predicates are missing:

term_variables_set(@Term, -Variables) is det

Same as term_variables_bag/2, but Variables is an ordered set.

subsumeschk(+Generic, @Specific) is semidet

SICStus 4 name of subsumes_chk/2.

deprecated: - Replace by subsumes_term/2.

term_order(@X, @Y, -R) is det

Same as compare/3, except for the order of arguments.

deprecated: - Use the standard compare/3 instead.

Re-exported predicates

The following predicates are exported from this file while their implementation is defined in imported modules or non-module files loaded by this module.

term_variables_bag(+Term, -Variables) is det

Variables is a list of variables that appear in Term. The variables are ordered according to depth-first left-right walking of the term. Variables contains no duplicates. This is the same as SWI-Prolog's term_variables/2.

contains_term(+Sub, +Term) is semidet

Succeeds if Sub is contained in Term (=, deterministically)

contains_var(+Sub, +Term) is semidet

Succeeds if Sub is contained in Term (==, deterministically)

free_of_term(+Sub, +Term) is semidet

Succeeds of Sub does not unify to any subterm of Term

free_of_var(+Sub, +Term) is semidet

Succeeds of Sub is not equal (==) to any subterm of Term

occurrences_of_term(@SubTerm, @Term, ?Count) is det

Count the number of SubTerms in Term that unify with SubTerm. As this predicate is implemented using backtracking, SubTerm and Term are not further instantiated. Possible constraints are enforced. For example, we can count the integers in Term using

?- freeze(S, integer(S)), occurrences_of_term(S, f(1,2,a), C).
C = 2,
freeze(S, integer(S)).

See also: - occurrences_of_var/3 for an equality (==/2) based variant.

occurrences_of_var(@SubTerm, @Term, ?Count) is det

Count the number of SubTerms in Term that are equal to SubTerm. Equality is tested using ==/2. Can be used to count the occurrences of a particular variable in Term.

See also: - occurrences_of_term/3 for a unification (=/2) based variant.

sub_term(-Sub, +Term)

Generates (on backtracking) all subterms of Term.

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.

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.

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)

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.