?Term =.. ?List

Term

Prolog term.

List

List or variable.

Description

Otherwise, either Term is instantiated to a compound term, or List is instantiated to a list, or both. In which case, ``univ'' unifies Term with functor(Arg1, Arg2, ..., ArgN), and List with [Functor', Arg1', Arg2', .., argN'], where functor is unified with Functor', Arg1 is unified with Arg1', etc. functor must be an atom, and it must be possible to determine the length of List from either Term or List.

Modes and Determinism

• =..(+, -) is det
• =..(-, +) is det

Exceptions

(5) type error

List is instantiated, but not to a list.

(4) instantiation fault

functor is not specified within Term or List (non-coroutine mode only).

(4) instantiation fault

The length of List cannot be determined (non-coroutine mode only).

Examples

   Success:
   Term =.. [likes,david,play]. (gives Term = likes(david,play)).
   s([1,4,5,6]) =.. List.       (gives List = [s,[1,4,5,6]]).
   zero_arity =.. List.         (gives List = [zero_arity]).
   1234 =.. List.               (gives List = [1234]).
   "string" =.. List.           (gives List = ["string"]).
   2.9 =.. List.                (gives List = [2.9]).
   f(1,X,3) =.. [Y,Z,2,W].      (gives X=2; Y=f; Z=1; W=3).
   f(1,X,3) =.. [A,B,C,D].      (gives A=f; B=1; C=2; D=3).
   f(A) =.. List.               (gives A=_g74; List=[f,_g74]).
   Term =.. [f,A].              (gives Term=f(_g76); A=_g76).
   f(1,2,3) =.. [f | A].        (gives A=[1,2,3]).
   a =.. [X].                   (gives X=a)
Fail:
  likes(man,play) =.. [likes,man,work].

Error:
  Term =.. List.        (Error 4).
  Term =.. [Var,1,2,3]. (Error 4). % functor of Term is
                                   %   not specified.
  Term =.. [f | A].     (Error 4). % arity of Term is
                                   %   not specified.
  Term =.. [f,a,b | X]. (Error 4).
  Term =.. my_atom.     (Error 5).
  Term =.. [1,2,3].     (Error 5).
  Term =.. [a|b].       (Error 5).
  Term =.. [f,a,b | c]. (Error 5).

See Also