Applies the given kills to a copy of env. named kills remove (or, when conditional,
weaken to maybe) a single definition; all kills clear the current frame; unknown kills weaken every
in-scope definition to maybe. Returns env unchanged when there is nothing to apply.
Applies the given kills to a copy of
env.namedkills remove (or, when conditional, weaken to maybe) a single definition;allkills clear the current frame;unknownkills weaken every in-scope definition to maybe. Returnsenvunchanged when there is nothing to apply.