Documentation

Check that if predicate holds for any inputs to the fold.

>>> run [1, 2, 3, 4] (any even)
True

>>> run [] (any $ const False)
False

Check that if predicate holds for all inputs to the fold.

>>> run [1, 2, 3, 4] (all (< 6))
True

>>> run [1, 2, 3, 4] (all (> 1))
False

Check whether all elements are True.

>>> run (repeat False) and
False

>>> run (repeat True) and
... diverges ...

Check whether any elements are True.

>>> run (True : repeat False) or
True
>>> run (repeat False) or
... diverges ...

Check whether an element is fed into the fold.

>>> run [1, 2, 3] (elem 3)
True

>>> run [] (elem 1)
False

Check whther an element isn't fed into the fold. >>> run [1, 2, 3] (notElem 3) False

>>> run [] (notElem 1)
True

Find the first element for which a predicate holds.

>>> run [1, 2, 3, 4] (find even)
Just 2

>>> run [1, 2, 3, 4] (find (> 4))
Nothing

Grab the first inputted element.

>>> run [1 ..] head
Just 1

>>> run [] head
Nothing

Check whether a fold was fed any elements.

>>> run [] null
True

>>> run [1..] null
False

Occasionally we want to use a short-circuiting fold with other, nonlazy folds. This function drops laziness on the floor for a L' fold. This is dangerous because it can potentially effect termination behavior.

>>> run (repeat False) and
False

>>> run (repeat False) (strictify and)
... diverges ...

This is generally an advantage when we want to combine a monoidal fold with a left one.

>>> run [1.0, 2, 3, 4] $ (/) <$> strictify head <*> maximum
0.25