import Control.Applicative

data C = C
data T = T
data P = P
data N = N deriving Eq
data S = S
data S' = S'

getParameterValuestoSeq :: C -> [T]
getParameterValuestoSeq = undefined

getParameter :: T -> P
getParameter = undefined

getVariableName :: P -> N
getVariableName = undefined

getValue :: T -> S'
getValue = undefined

option :: S' -> Maybe S
option = undefined

getDefaultValue :: P -> S
getDefaultValue = undefined

headOption :: [x] -> Maybe x
headOption = undefined -- listToMaybe

getOrElse :: x -> Maybe x -> x
getOrElse = undefined -- fromMaybe

f :: C -> N -> Maybe S
f scenario name = headOption . fmap (\t -> getDefaultValue (getParameter t) `getOrElse` option (getValue t)) $ filter (\t -> getVariableName (getParameter t) == name) (getParameterValuestoSeq scenario)

f' :: C -> N -> Maybe S
f' scenario name =
  let z = headOption $ filter (\t -> getVariableName (getParameter t) == name) (getParameterValuestoSeq scenario)
  in fmap ((getOrElse . getDefaultValue . getParameter) <*> (option . getValue)) z