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|
module student
// Laurens Kuiper (s4467299)
// Camil Staps (s4498062)
// Example output:
// Your first name please: Camil
// Your last name please: Staps
// Your student number please: 4498062
// {Student|fname=Camil,lname=Staps,snum=4498062}
import StdEnv, StdMaybe, monad
/*
* Pieter Koopman, pieter@cs.ru.nl
* Advanced Programming, week 4
*/
// ---- an IO monad with maybe results --- //
:: *State = {w :: *World, c :: *Maybe *File}
:: IO a = IO (State -> *(Maybe a, State))
open :: State -> State
open {w, c=Nothing}
# (console, w) = stdio w
= {w = w, c = Just console}
open s = s
close :: State -> State
close { w, c=Just f} = { w = snd (fclose f w), c = Nothing}
close s = s
unIO :: (IO a) -> State -> *(Maybe a, State)
unIO (IO f) = f
run :: (IO a) *World -> *World
run m w = (close (snd (unIO m {w=w, c=Nothing}))).w
// ---- reading from console --- //
class read a :: IO a
instance read String where
read = IO r where
r s
#! {w,c=Just c} = open s
(line, c) = freadline c
s = rmNL line
| size s > 0
= (Just s,{w = w, c = Just c})
#! c = c <<< "String must be not empty "
(line, c) = freadline c
s = rmNL line
| size s > 0
= (Just s, {w = w, c = Just c})
= (Nothing, {w = w, c = Just c})
instance read Int where
read = IO r where
r s
#! {w,c=Just c} = open s
(b,i,c) = freadi c
| b
= (Just i, {w = w, c = Just c})
#! (_, c) = freadline c
c = c <<< "An integer please "
(b,i,c) = freadi c
| b
= (Just i, {w = w, c = Just c})
#! (_, c) = freadline c
= (Nothing, {w = w, c = Just c})
write :: String -> IO String
write mess = IO w where
w s
#! {w,c=Just c} = open s
= (Just mess,{w=w,c=Just (c <<< mess)})
// ---- make IO a monad --- //
instance Functor IO where
fmap f (IO g)
= IO \s.case g s of
(Just a, s) = (Just (f a),s)
(Nothing,s) = (Nothing , s)
instance Applicative IO where
pure a = IO \s.(Just a, s)
(<*>) (IO f) (IO g) = IO \s.case f s of
(Just f,s) = case g s of
(Just a,s) = (Just (f a),s)
(n, s) = (Nothing, s)
(n, s) = (Nothing, s)
instance Monad IO where
bind (IO f) g = IO \s.case f s of
(Just a, s) = unIO (g a) s
(n, s) = (Nothing, s)
instance fail IO where fail = IO \s.(Nothing,s)
instance OrMonad IO where
<|> (IO f) (IO g) =
IO \s.case f s of
(Nothing, s) = g s
other = other
// ---- reading a student record --- //
Start w = run (f3 >>= write o toString <|> write "Failed\n") w
:: Student =
{ fname :: String
, lname :: String
, snum :: Int
}
instance toString Student where
toString {fname,lname,snum} = "{Student|fname=" + fname + ",lname=" + lname + ",snum=" + toString snum + "}"
instance + String where + s t = s +++ t
f0 :: *World -> (Student, *World)
f0 world = ({fname = rmNL fname, lname = rmNL lname, snum = snum}, world2) where
(console1, world1) = stdio world
console2 = console1 <<< "Your first name please: "
(fname,console3) = freadline console2
console4 = console3 <<< "Your last name please: "
(lname,console5) = freadline console4
console6 = console5 <<< "Your student nmber please: "
(b1,snum,console7) = freadi console6
(b2, world2) = fclose console7 world1
f1 :: *World -> (Student, *World)
f1 world
#! (console, world) = stdio world
console = console <<< "Your first name please: "
(fname,console) = freadline console
console = console <<< "Your last name please: "
(lname,console) = freadline console
console = console <<< "Your student nmber please: "
(b1,snum,console) = freadi console
(b2, world) = fclose console world
= ({fname = rmNL fname, lname = rmNL lname, snum = snum}, world)
f2 :: IO String
f2
= ( write "Your first name please: "
>>| read
>>= \fname.write "Your last name please: "
>>| read
>>= \lname.write "Your student nmber please: "
>>| read
>>= \snum. rtrn {fname = rmNL fname, lname = rmNL lname, snum = snum}
>>= write o toString)
<|> write "failed to read a student"
f3 :: IO Student
f3 =
(\f l s -> {fname=rmNL f, lname=rmNL l, snum=s}) <$>
input "Your first name please: " <*>
input "Your last name please: " <*>
input "Your student number please: "
where
input :: String -> IO a | read a
input s = write s *> read
// It would really be much easier if we would use Platform from the start in this course.
(*>) infixl 4 :: (f a) (f b) -> f b | Applicative f
(*>) fa fb = id <$ fa <*> fb
(<$) infixl 4 :: a (f b) -> f a | Functor f
(<$) x fa = fmap (const x) fa
rmNL :: String -> String
rmNL string
# len = size string
| len > 0 && string.[len-1] == '\n'
= string % (0, len - 2)
= string
|
