问题
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]}
回答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).
回答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.
来源：https://stackoverflow.com/questions/6347091/parse-variables-using-dcg