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Predicate code_type/2
Availability:built-in
code_type(?Code, ?Type)
As char_type/2, but uses character codes rather than one-character atoms. Please note that both predicates are as flexible as possible. They handle either representation if the argument is instantiated and will instantiate only with an integer code or a one-character atom, depending of the version used. See also the Prolog flag double_quotes, atom_chars/2 and atom_codes/2.
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LogicalCaptain said (2021-02-19T13:13:20):0 upvotes 0 0 downvotes
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Example:

Taking the code for 0 :

?- code_type(0'0,X).
X = alnum ;
X = csym ;
X = prolog_identifier_continue ;
X = ascii ;
X = digit ;
X = graph ;
X = to_lower(48) ;
X = to_upper(48) ;
X = digit(0) ;
X = xdigit(0).

Taking the (unicode) code for the "forall" sign (see https://en.wikipedia.org/wiki/Mathematical_operators_and_symbols_in_Unicode)

?- code_type(0x2200,X).
X = prolog_symbol ;
X = graph ;
X = punct ;
X = period ;
X = quote ;
X = to_lower(8704) ;
X = to_upper(8704) ;
false.

code_type/2 works for both codes and chars as argument Code, which makes it easy to use in DCGs which may be fed codes or chars without obnoxious case decisions:

any_digits([C|Cs]) --> [C],{code_type(C,digit)},!,any_digits(Cs).
any_digits([])     --> [].

accept_any_digits(Atom,Acc,Rest,How) :-
   assertion(member(How,[chars,codes])),
   explode(How,Atom,List),
   phrase(any_digits(Acc),List,Rest).

explode(chars,Atom,List) :- atom_chars(Atom,List).
explode(codes,Atom,List) :- atom_codes(Atom,List).

The above works irrespective of whether we feed a list of chars or a list of codes to the DCG, and even though we only use code_type/2:

?- accept_any_digits('01276x',Acc,Rest,codes).
Acc = [48,49,50,55,54],
Rest = [120].

?- accept_any_digits('01276x',Acc,Rest,chars).
Acc = ['0','1','2','7','6'],
Rest = [x].