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Today's Topics:
1. Re: data design for a questionnaire (retitled + update) (Alia)
2. help opengl object (Song Zhang)
3. Re: data design for a questionnaire (retitled + update) (Alia)
----------------------------------------------------------------------
Message: 1
Date: Wed, 23 Nov 2011 03:07:20 -0800 (PST)
From: Alia <[email protected]>
Subject: Re: [Haskell-beginners] data design for a questionnaire
(retitled + update)
To: "[email protected]" <[email protected]>
Message-ID:
<[email protected]>
Content-Type: text/plain; charset="iso-8859-1"
Hi folks,
As a follow-on question from my prior post, I got stuck on not being able to
compile the following
code in my survey data model which basically generally unwraps the the inner
type from the
wrapper:
extract :: Question' -> Question a
extract q = case q of
??? QuestionS x -> extractQString q
??? QuestionI x -> extractQInt q
??? QuestionD x -> extractQDouble q
and I had to produce the following instead:
extractQString :: Question' -> Question String
extractQString (QuestionS q) = q
extractQInt :: Question' -> Question Int
extractQInt (QuestionI q) = q
extractQDouble :: Question' -> Question Double
extractQDouble (QuestionD q) = q
An exchange in stackoverflow seems to suggest that the only way to do it is to
use GADTs (which is a language extension).
http://stackoverflow.com/questions/6047522/haskell-type-and-pattern-matching-question-extracting-fields-from-a-data-type
I'm disinclined to use language extensions because I'd rather use haskell98
proper to begin with. So Is this indeed the case?
?My code has become more verbose as a result and I am trying to learn most
elegant and general haskell 'way' (if it exists)
and hence I would appreciate any advice to this end.
regards,
Alia
<survey.hs>
module Main where
import Text.Show.Functions
import Data.Maybe
type Name??????????? = String
type QuestionText??? = String
type Answer????????? = String
type Score?????????? = Double
type CorrectAnswer a = a
type Option a??????? = (String, a)
-- type converters
str????? = id
int s??? = read s :: Int
double s = read s :: Double
data QuestionType?? = Open
??????????????????? | Test
??????????????????? | Choice
????????????????????? deriving (Show, Eq)
data Question a = Question
??? { questionName??? :: Name
??? , questionText??? :: QuestionText
??? , questionType??? :: QuestionType
??? , answerFunc????? :: (String -> a)
??? , correctAnswer?? :: Maybe a
??? , options???????? :: Maybe [Option a]
??? } deriving (Show)
data Question' = QuestionS (Question String)
?????????????? | QuestionI (Question Int)
?????????????? | QuestionD (Question Double)?
???????????????? deriving (Show)
data QuestionSet = QuestionSet
??? { qsetTitle???? :: String
??? , qsetQuestions :: [Question']
??? , qsetPoints??? :: Double
??? } deriving (Show)
data Survey = Survey
??? { surveyTitle??????? :: String
??? , surveyQuestionSets :: [QuestionSet]
??? } deriving (Show)
parse :: Question a -> Answer -> a
parse = answerFunc
view? :: Question a -> String
view q = questionName q
ask?? :: Question a -> IO ()
ask q = putStrLn $ questionText q
store :: Question a -> Answer -> IO ()
store q ans = putStrLn $ questionName q ++ ": " ++ show ans
{-
extract :: Question' -> Question a
extract q = case q of
??? QuestionS x -> extractQString q
??? QuestionI x -> extractQInt q
??? QuestionD x -> extractQDouble q
-}
extractQString :: Question' -> Question String
extractQString (QuestionS q) = q
extractQInt :: Question' -> Question Int
extractQInt (QuestionI q) = q
extractQDouble :: Question' -> Question Double
extractQDouble (QuestionD q) = q
testQ :: (Eq a) => Question a -> Answer -> Bool
testQ q ans = case (correctAnswer q) of
??? Nothing -> False
??? Just x? -> x == (answerFunc q $ ans)
testQ' :: Question' -> Answer -> Bool
testQ' q a = case q of
??? QuestionS x -> testQS q a
??? QuestionI x -> testQI q a
??? QuestionD x -> testQD q a
??? where
??????? testQS q a = testQ (extractQString q) a
??????? testQI q a = testQ (extractQInt??? q) a
??????? testQD q a = testQ (extractQDouble q) a
testQset :: QuestionSet -> [Answer] -> [Bool]
testQset qs as = zipWith testQ' (qsetQuestions qs) as
evalQset :: QuestionSet -> [Answer] -> Score
evalQset qs as = (total_correct / total_questions) * score
??? where
??????? total_questions = fromIntegral (length $ qsetQuestions qset)
??????? total_correct = fromIntegral (length $ filter (== True) (testQset qset
as))
??????? score = qsetPoints qset
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? = "q3"
??? , questionText? = "What is 2+1?"
??? , questionType? = Choice
??? , answerFunc??? = int
??? , correctAnswer = Just 3
??? , options?????? = Just [("a", 2), ("b", 3), ("c", 4)]
??? }
q4 = Question
??? { questionName? = "q4"
??? , questionText? = "What is 2.0 + 1.5 ?"
??? , questionType? = Choice
??? , answerFunc??? = double
??? , correctAnswer = Just 3.5
??? , options?????? = Just [("a", 2.1), ("b", 3.5), ("c", 4.4)]
??? }
qset = QuestionSet
??? { qsetTitle???? = "simple questions"
??? , qsetQuestions = [ QuestionS q1
????????????????????? , QuestionI q2
????????????????????? , QuestionI q3
????????????????????? , QuestionD q4
????????????????????? ]
??? , qsetPoints??? = 100.0
??? }
survey = Survey
??? { surveyTitle??????? = "a survey"
??? , surveyQuestionSets = [qset]
??? }
???
t1 = evalQset qset ["1", "2", "3", "4"]
</survey.hs>
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Message: 2
Date: Wed, 23 Nov 2011 22:58:26 +0000
From: Song Zhang <[email protected]>
Subject: [Haskell-beginners] help opengl object
To: [email protected]
Message-ID:
<CACGMEOnX-5HOOjUPY2htsCx5C2nEFGvy=zdddq5gl0ooow+...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
Hi
in Graphics.UI.GLUT.Objects
there are some pre-defined object such as cube or cone
I tried to draw objects in haskell but get black screen
who can give me some examples to draw these objects
and for drawing Cylinder in the documentation what is (*freeglut
only) *means. do I need glut32.dll to render these object in windows?
thanks
--
the University of Nottingham, CS school
the representative of SSFC CS school
Staff of SIFEUNNC IT department
I am Ice which is sleeping water.
Sent via BlackBerry? by BerryMail
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Message: 3
Date: Thu, 24 Nov 2011 01:32:47 -0800 (PST)
From: Alia <[email protected]>
Subject: Re: [Haskell-beginners] data design for a questionnaire
(retitled + update)
To: "[email protected]" <[email protected]>
Message-ID:
<[email protected]>
Content-Type: text/plain; charset="iso-8859-1"
Hi folks,
As the code (from my prior post) is not so relevant to the issue
at hand, it was quite reasonably suggested that I should simplify my
question somewhat. So here goes:
In my model, I have a Question record type, which has a type parameter
to take into account that answers can be evaluated to different types.
For example, I can ask a question which requires a Double as an
answer and another which requires an Int as an answer:
data Question a = Question {text:: String, answer:: Maybe a}
This question type is wrapped/boxed in another type to allow the
different questions to referenced in a list. Hence,
data Question' = QuestionS (Question String)
?????????????? | QuestionI (Question Int)
?????????????? | QuestionD (Question Double)
and I can now store the questions as follows:
questions = [ QuestionI {text="What's 1+1?", answer=Maybe 2}
??????????? , QuestionD {text="What's 1.0+1.5?", answer=Maybe 2.5}
??????????? ]
Now to extract Question a from Question' I would have liked to write
the following:
extract :: Question' -> Question a
extract q = case q of
??? QuestionS x -> extractQString q
??? QuestionI x -> extractQInt q
??? QuestionD x -> extractQDouble q
but instead, I had to produce the following instead:
extractQString :: Question' -> Question String
extractQString (QuestionS q) = q
extractQInt :: Question' -> Question Int
extractQInt (QuestionI q) = q
extractQDouble :: Question' -> Question Double
extractQDouble (QuestionD q) = q
>From what I understand so far, that specialized extraction or unboxing
functions are the way to go unless one uses language extensions like
GADTs which can be conceptually more complicated. Is this indeed the case,
or are there other ways to achieve generalized type unboxing while
remaining within the Haskell98 specification?
Best,
Alia
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