findM is:exact

Like find, but where the test can be monadic.

findM (Just . isUpper) "teST"             == Just (Just 'S')
findM (Just . isUpper) "test"             == Just Nothing
findM (Just . const True) ["x",undefined] == Just (Just "x")

A generalization of findM to Foldable instances.

Returns the first element that satisfies the given predicate.

findM = Stream.fold Fold.findM

Returns the first element that satisfies the given predicate. Pre-release

Like find, but takes a monadic function instead; retains the short-circuiting behaviour of the non-monadic version. For example,

findM (\a -> putStr (show a <> " ") >> pure False) [1..10]

would print "1 2 3 4 5 6 7 8 9 10" and return Nothing, while

findM (\a -> putStr (show a <> " ") >> pure True) [1..10]

would print "1" and return Just 1.

Yield Just the first element that satisfies the monadic predicate or Nothing if no such element exists.