Parse Variables Using DCG

Question

I am having trouble parsing sequences that begin with capital letters into variables using Prolog's DCG notation. For instance, if I have the string

f a X y Z X

and a DCG that parses this string, is there any way to parse each capitalized letter into a unique Prolog variable. E.g., parse Y to a variable and each X to a variable? The intended application would be to build the functor

T = f(a,X,y,Z,X)

via a DCG rule ending with the statement

{T =.. [Head|Args]}

Answer 1

Maybe you are looking for term_to_atom/3:

?- term_to_atom(Term, 'f(a,X,y,Z,X)').
Term = f(a, _G304, y, _G306, _G304).

Answer 2

If you are using capital letters as an atom, you have to surround them between single quotes. E.g. 'X' and 'Z'.

Otherwise, they will be considered as prolog variables.