prolog program to check whether a given input is digit or uppercase or lowercase

Question

I have used the following logic for above program but it gives error showing >=/2: Arithmetic: 'a/0' is not a function. What should i do to correct the program?

digit(X):- X>=0,X<10,write('input is digit').
uppercase(X):- X>='A',X<'[',write('input is uppercase').
lowercase(X):- X>='a',X<'{',write('input is lowercase').

Thanks

Answer 1

If you want to classify just the ASCII characters in ISO Prolog, you can do this in various ways:

As characters which are represented as atoms of length 1. To compare them you can use the general term comparison (@>=)/2, (@>)/2 ... In your example, that would be:

digit_char(X) :- atom_length(X,1), X @>= '0', X @=< '9'.
...

As character codes which are plain integers representing the collating sequence integer (sounds impressive? Its just the ASCII-code).

digit_code(X) :- integer(X), X >= 0'0, X =< 0'9.
...

If you need to convert between both, there is char_code/2.

For Unicode, things are not yet generally available and agreed upon. In SWI, there is char_type/2 and code_type/2. Beware, these things are still evolving...

For more about characters and codes, see What is the difference between ' and " in Prolog?