Replaces a non-interpolated ~w or ~W word list with an empty list and a one-element sentinel list:
~w(a b)→~w()~w(a b)→~w(mutare)
The sigil modifier is retained, so a and c word lists keep atom and charlist elements. Equivalent replacements are detected from the parsed words rather than the raw source; for example, a whitespace-only word list does not produce another empty-list mutant.
Interpolated ~w sigils are not mutated. ~W never interpolates.
On the right side of a guard in, the empty replacement is suppressed because membership in an empty list is already covered by Mutare.Mutators.Conditional. The sentinel replacement remains eligible. Body in expressions keep the empty replacement because left-side evaluation is observable.
The ignore variants are empty and sentinel.