[ Comparing and Sorting | Reference Manual | Alphabetic Index ]
occurs(?Simple, ?Term)
Succeeds if Simple is a variable or an atomic type that occurs in the term
Term.
- Simple
- Variable or atomic type.
- Term
- An arbitrary term.
Description
   Succeeds if Simple is a variable, an atom or a number occurring in the
   term Term.
Modes and Determinism
Fail Conditions
Fails if Simple does not occur in the term Term.
Exceptions
- (5) type error 
- If Simple is neither a variable, an atom nor a number.
Examples
   Success:
   occurs(a,a).
   occurs(X,f(a,b,c,X)).
   occurs(+,f(+,-)).
   occurs(a,[b,c,a,g,a]).
   occurs([ ],[a,b]).
   occurs(1,[A|1]).
   occurs(1.0,[1.0|B]).
   Fail:
   occurs(a,b).
   occurs(X,f(Y,Z)).
   occurs(X,Y).
   occurs(1,"2314").
   occurs([], [a,b|c]).
   Error:
   occurs("str",f("str1","str2","str")). (Error 5)
   occurs([a],[a,b]).                    (Error 5)
   occurs(f(a,b),f(a,b)).                (Error 5)
See Also
instance / 2, variant / 2