Problem Statement

Idiomatically determine all the lowercase and uppercase letters   (of the Latin [English] alphabet)   being used currently by a computer programming language. The method should find the letters regardless of the hardware architecture that is being used (ASCII, EBCDIC, or other).

Display the set of all: that can be used (allowed) by the computer program, where   letter   is a member of the Latin (English) alphabet:     a ──► z     and     A ──► Z.

You may want to mention what hardware architecture is being used, and if applicable, the operating system.

Let's start with the solution:

chars :-    
    findall(Lower, maplist(char_type(Lower), [alpha, ascii, lower]), Lowers),
    
    writeln('-- Lower Case Characters --'), 
    writeln(Lowers),
    nl,

    findall(Upper, maplist(char_type(Upper), [alpha, ascii, upper]), Uppers),
    writeln('-- Upper Case Characters --'),
    writeln(Uppers).