Prolog predicates can be given the role of arithmetic function. The last argument is used to return the result, the arguments before the last are the inputs. Arithmetic functions are added using the predicate arithmetic_function/1, which takes the head as its argument. Arithmetic functions are module sensitive, that is they are only visible from the module in which the function is defined and delared. Global arithmetic functions should be defined and registered from module user. Global definitions can be overruled locally in modules. The builtin functions described above can be redefined as well.
>/2
,
etc.). The Prolog predicate should have one more argument than
specified by Head, which it either a term Name/Arity, an
atom or a complex term. This last argument is an unbound variable at
call time and should be instantiated to an integer or floating point
number. The other arguments are the parameters. This predicate is
module sensitive and will declare the arithmetic function only for the
context module, unless declared from module user. Example:
1 ?- [user]. :- arithmetic_function(mean/2). mean(A, B, C) :- C is (A+B)/2. user compiled, 0.07 sec, 440 bytes. Yes 2 ?- A is mean(4, 5). A = 4.500000