identity package:leancheck

identity :: Eq a => (a -> a) -> a -> Bool

Deprecated: Use isIdentity.

Is the given function an identity? f x == x

> check $ isIdentity (+0)
+++ OK, passed 200 tests.

> check $ isIdentity (sort :: [()]->[()])
+++ OK, passed 200 tests.

> check $ isIdentity (not . not)
+++ OK, passed 2 tests (exhausted).

Is the given function never an identity? f x /= x

> check $ neverIdentity not
+++ OK, passed 2 tests (exhausted).

> check $ neverIdentity negate
*** Failed! Falsifiable (after 1 tests):
0

Note: this is not the same as not being an identity.

Deprecated: Use isNeverIdentity.