terms_functor(?Structs, ?Length, ?Name, ?Arity)

Structs

List of terms, or variable

Length

Integer or variable

Name

Atomic or variable

Arity

Integer or variable

Description

Succeeds if Structs is a list of length Length, whose elements all have the same functor Name/Arity. Operationally, this can be used to either generate a list with of this form, or to check whether an existing list corresponds to it.

This is (modulo nondeterminism) similar to

    ( foreach(S,Structs), count(_,1,Length), param(Name,Arity) do
        functor(S,Name,Arity)
    )

Note that (like in the underlying functor/3 predicate), if Arity is zero, Name can be any atomic term (including number or string).

Modes and Determinism

• terms_functor(-, +, +, +) is det
• terms_functor(-, -, +, +) is multi
• terms_functor(+, -, -, -) is semidet
• terms_functor(-, +, -, -) is erroneous

Fail Conditions

Exceptions

(4) instantiation fault

Arguments are insufficiently instantiated

(5) type error

Name is not atomic

(5) type error

Arity is not an integer

(5) type error

Arity is greater than 0 and Name is not an atom

(6) out of range

Arity is negative

Examples

    % fill a list with structure skeletons
    ?- terms_functor(Ss, 3, f, 2).
    Ss = [f(_275,_276), f(_278,_279), f(_281,_282)]
    Yes (0.00s cpu)

    % check whether all elements have same toplevel functor
    ?- terms_functor([f(a),f(b)], L, F, A).
    L = 2
    F = f
    A = 1
    Yes (0.00s cpu)

    % complete a list acccording to a prototype
    ?- terms_functor([f(a)|Ss], 4, _, _).
    Ss = [f(_190), f(_194), f(_198)]
    Yes (0.00s cpu)

    % fill a list with an atomic term (arity 0)
    ?- terms_functor(Ss, 3, 99, 0).
    Ss = [99, 99, 99]
    Yes (0.00s cpu)

See Also