Alternative orelse operator that allows to select which exception should be used.
The default is to use the first exception since the standard
orelse uses the second.
tryFinally' x fruns
xand then the "finally" computation
a : α,
f (some a)is returned. If
m's definition of failure,
f noneis returned. Hence
tryFinally'can be thought of as performing the same role as a
finallyblock in an imperative programming language.
x and then execute
finalizer even if
x threw an exception