isNothing :: Maybe A -> Bool
-- testing 3 combinations of argument values
-- pruning with 0/0 rules
-- 2 candidates of size 1
-- 1 candidates of size 2
-- tested 3 candidates
isNothing Nothing  =  True
isNothing (Just x)  =  False

isJust :: Maybe A -> Bool
-- testing 3 combinations of argument values
-- pruning with 0/0 rules
-- 2 candidates of size 1
-- 1 candidates of size 2
-- tested 3 candidates
isJust Nothing  =  False
isJust (Just x)  =  True

fromMaybe :: A -> Maybe A -> A
-- testing 4 combinations of argument values
-- pruning with 0/0 rules
-- 1 candidates of size 1
-- 1 candidates of size 2
-- tested 2 candidates
fromMaybe x Nothing  =  x
fromMaybe x (Just y)  =  y

maybe :: A -> (A -> A) -> Maybe A -> A
-- pruning with 0/0 rules
-- 1 candidates of size 1
-- 2 candidates of size 2
-- 5 candidates of size 3
-- tested 6 candidates
maybe x f Nothing  =  x
maybe x f (Just y)  =  f y

listToMaybe :: [A] -> Maybe A
-- testing 4 combinations of argument values
-- pruning with 0/0 rules
-- 1 candidates of size 1
-- 0 candidates of size 2
-- 1 candidates of size 3
-- tested 2 candidates
listToMaybe []  =  Nothing
listToMaybe (x:xs)  =  Just x

maybeToList :: Maybe A -> [A]
-- testing 4 combinations of argument values
-- pruning with 0/0 rules
-- 1 candidates of size 1
-- 0 candidates of size 2
-- 0 candidates of size 3
-- 1 candidates of size 4
-- tested 2 candidates
maybeToList Nothing  =  []
maybeToList (Just x)  =  [x]

catMaybes :: [Maybe A] -> [A]
-- testing 44 combinations of argument values
-- pruning with 0/0 rules
-- 1 candidates of size 1
-- 0 candidates of size 2
-- 0 candidates of size 3
-- 0 candidates of size 4
-- 0 candidates of size 5
-- 1 candidates of size 6
-- 2 candidates of size 7
-- tested 4 candidates
catMaybes []  =  []
catMaybes (Nothing:mxs)  =  catMaybes mxs
catMaybes (Just x:mxs)  =  x:catMaybes mxs

