similar to isNothing

>>> pz @IsNothing (Just 123)
Val False

>>> pz @IsNothing Nothing
Val True

>>> pl @(Not IsNothing &&& ('Just Id >> Id + 12)) (Just 1)
Present (True,13) ('(True,13))
Val (True,13)

>>> pl @(Not IsNothing &&& ('Just Id >> Id + 12)) Nothing
Error 'Just(empty) ('(,))
Fail "'Just(empty)"

similar to isJust

>>> pz @IsJust Nothing
Val False

>>> pz @IsJust (Just 'a')
Val True

constructs a Nothing for a given type

constructs a Nothing for a given type

Just constructor

>>> pz @(MkJust Id) 44
Val (Just 44)

similar to fromJust

>>> pz @(Just' >> Succ) (Just 20)
Val 21

>>> pz @(Just' >> Succ) Nothing
Fail "Just' found Nothing"

extract the value from a Maybe otherwise use the default value: similar to fromMaybe

>>> pl @(JustDef 'True Id) Nothing -- preserves TrueP/FalseP in the default case
True (JustDef Nothing)
Val True

>>> pl @(JustDef (Fst > 12) Snd) (3,Just False) -- ValP for normal case
Present False (JustDef Just)
Val False

>>> pl @(JustDef Fst Snd) (True,Nothing)
Present True (JustDef Nothing)
Val True

>>> pz @(JustDef (1 % 4) Id) (Just 20.4)
Val (102 % 5)

>>> pz @(JustDef (1 % 4) Id) Nothing
Val (1 % 4)

>>> pz @(JustDef (MEmptyT _) Id) (Just "xy")
Val "xy"

>>> pz @(JustDef (MEmptyT _) Id) Nothing
Val ()

>>> pz @(JustDef (MEmptyT (SG.Sum _)) Id) Nothing
Val (Sum {getSum = 0})

>>> pl @(JustDef 0 Id) (Just 123)
Present 123 (JustDef Just)
Val 123

>>> pl @(JustDef 0 Id) Nothing
Present 0 (JustDef Nothing)
Val 0

>>> pl @(JustDef 99 Id) (Just 12)
Present 12 (JustDef Just)
Val 12

>>> pl @(JustDef 99 Id) Nothing
Present 99 (JustDef Nothing)
Val 99

>>> pl @(JustDef (99 -% 1) Id) Nothing
Present (-99) % 1 (JustDef Nothing)
Val ((-99) % 1)

>>> pl @(JustDef (MEmptyT _) Id) (Just (SG.Sum 123))
Present Sum {getSum = 123} (JustDef Just)
Val (Sum {getSum = 123})

>>> pl @(JustDef (MEmptyT _) Id) (Nothing @(SG.Sum _))
Present Sum {getSum = 0} (JustDef Nothing)
Val (Sum {getSum = 0})

extract the value from a Maybe or fail with the given message

>>> pz @(JustFail "nope" Id) (Just 99)
Val 99

>>> pz @(JustFail "nope" Id) Nothing
Fail "nope"

>>> pz @(JustFail (PrintF "oops=%d" Snd) Fst) (Nothing, 123)
Fail "oops=123"

>>> pz @(JustFail (PrintF "oops=%d" Snd) Fst) (Just 'x', 123)
Val 'x'

like mapMaybe

>>> pl @(MapMaybe (MaybeBool (Le 3) Id) Id) [1..5]
Present [1,2,3] ((>>) [1,2,3] | {Concat [1,2,3] | [[1],[2],[3],[],[]]})
Val [1,2,3]

>>> pl @(MapMaybe (MaybeBool (Gt 3) Id) Id) [1..5]
Present [4,5] ((>>) [4,5] | {Concat [4,5] | [[],[],[],[4],[5]]})
Val [4,5]

similar to catMaybes

>>> pl @CatMaybes [Just 'a',Nothing,Just 'c',Just 'd',Nothing]
Present "acd" ((>>) "acd" | {Concat "acd" | ["a","","c","d",""]})
Val "acd"

Convenient method to convert a value p to a Maybe based on a predicate b if b then Just p else Nothing

>>> pz @(MaybeBool (Id > 4) Id) 24
Val (Just 24)

>>> pz @(MaybeBool (Id > 4) Id) (-5)
Val Nothing

>>> pz @(MaybeBool 'True 10) ()
Val (Just 10)

destructs an Maybe value n Nothing receives (PP s x,Proxy result) (you can use the proxy with MEmptyP) p Just a receives (PP s x,a) s points to the environment you want to pass in t points to the Maybe value

>>> pz @(MaybeIn Fst Snd Fst Snd) ('a', Just 'x')
Val 'x'

>>> pz @(MaybeIn Fst Snd Fst Snd) ('a', Nothing)
Val 'a'

>>> pl @(MaybeIn "none" "just"() Id) (Just (SG.Sum 12))
Present "just" (MaybeIn(Just) "just" | Sum {getSum = 12})
Val "just"

>>> pl @(MaybeIn (Snd >> FailP "oops") Snd Fst Snd) ("abc", Nothing)
Error oops (Proxy | MaybeIn(Nothing) n failed)
Fail "oops"

>>> pl @(MaybeIn (Snd >> MEmptyP) Snd Fst Snd) ("abc", Nothing)
Present () (MaybeIn(Nothing) () | ())
Val ()

simple version of MaybeIn with Id as the Maybe value and the environment set to ()

>>> pz @(MaybeId '("x","oops") '(Id,"fromjust")) (Just "ok")
Val ("ok","fromjust")

>>> pz @(MaybeId '("x","oops") '(Id,"fromjust")) Nothing
Val ("x","oops")

>>> pz @(MaybeId "found nothing" (ShowP Pred)) (Just 20)
Val "19"

>>> pz @(MaybeId "found nothing" (ShowP Pred)) Nothing
Val "found nothing"

>>> pl @(MaybeId 'True Id) Nothing
True (MaybeIn(Nothing) True | ())
Val True

>>> pl @(MaybeId 'True IdBool) (Just False)
False (MaybeIn(Just) False | False)
Val False

>>> pl @(MaybeId (FailT _ "failed4") Id) (Just 10)
Present 10 (MaybeIn(Just) 10 | 10)
Val 10

>>> pl @(MaybeId 'False Id) Nothing
False (MaybeIn(Nothing) False | ())
Val False

>>> pl @(MaybeId (FailT _ "err") Id) Nothing
Error err (Proxy | MaybeIn(Nothing) n failed)
Fail "err"

>>> pz @(MaybeId 99 Id) (Just 12)
Val 12

>>> pz @(MaybeId 99 Id) Nothing
Val 99

>>> pl @(MaybeId MEmptyP Ones) (Just "ab")
Present ["a","b"] (MaybeIn(Just) ["a","b"] | "ab")
Val ["a","b"]

>>> pl @(MaybeId MEmptyP Ones) Nothing
Present [] (MaybeIn(Nothing) [] | ())
Val []

>>> pl @(MaybeId MEmptyP (Fst ==! Snd)) (Just ('x','z'))
Present LT (MaybeIn(Just) LT | ('x','z'))
Val LT

>>> pl @(MaybeId MEmptyP (Fst ==! Snd)) (Nothing @(Char,Char))
Present EQ (MaybeIn(Nothing) EQ | ())
Val EQ

calculate the return type for MaybeIn