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

All list elements have the given functor or atomic value
List of terms, or variable
Integer or variable
Atomic or variable
Integer or variable


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

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

Fail Conditions

Not all list elements have the same functor, or the list is not of the given length


(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


    % 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

functor / 3, lists : length / 2