Normalization of gaps in Prolog atoms

Question

What is the best way to normalize whitespace (space, new line, tab) in the Prolog atom, for example. in SWI-Prolog. That is, I would like to have a rule:

normalize_space_in_atom(+Atom1, -Atom2)

such that Atom2

• has any sequence of space characters turned into one space
• starts with a non-space
• ends with a non-space

Answer 1

SWI Prolog provides normalize_space / 2, so you can define your predicate as follows:

normalize_space_in_atom(A1,A2) :- normalize_space(atom(A2),A1).

I tried this with SWI Prolog 5.7.5 and it seems to work. You can add additional error handling if you want.