As a followup, I just received a simpler and more elegant solution due to Lorenzo Bolla which involves wrapping
the question type in another type and achieves the objective nicely. I think this is much cleaner than
using existential types as per my prior posting.
module Main where
import Text.Show.Functions
-- type converters
str = id
int s = read s :: Int
float s = read s :: Double
data QuestionType = Open | Test | Choice deriving (Show, Eq)
data Question a = Question
{ questionName :: String
, questionText :: String
, questionType :: QuestionType
, answerFunc :: (String -> a)
, correctAnswer :: Maybe a
, options :: Maybe [(String, a)]
} deriving (Show)
data Question' = QuestionS (Question String) | QuestionI (Question Int) deriving (Show)
data QuestionSet a = QuestionSet
{ qsetTitle :: String
, qsetQuestions :: [Question']
} deriving (Show)
data Questionnaire a = Questionnaire
{ questionnaireTitle :: String
, questionnaireQuestionSets :: [QuestionSet a]
} deriving (Show)
q1 = Question
{ questionName = "q1"
, questionText = "What is our name?"
, questionType = Open
, answerFunc = id
, correctAnswer = Nothing
, options = Nothing
}
q2 = Question
{ questionName = "q2"
, questionText = "What is 1+1?"
, questionType = Test
, answerFunc = int
, correctAnswer = Just 2
, options = Nothing
}
q3 = Question
{ questionName = "q2"
, questionText = "What is 2+1?"
, questionType = Choice
, answerFunc = int
, correctAnswer = Just 3
, options = Just [("a", 2), ("b", 3), ("c", 4)]
}
qset = QuestionSet
{ qsetTitle = "simple questions"
, qsetQuestions = [QuestionS q1, QuestionI q2, QuestionI q3]
}
questionnaire = Questionnaire
{ questionnaireTitle = "a questionnaire"
, questionnaireQuestionSets = [qset]
}
Alia
