Night Owl 6/Night Owl's Shareware - PDSI-006 - Night Owl Corp (1990).iso/016a/gofer221.zip/PRELUDE

Text File | 1991-11-20 | 26KB | 789 lines

--         __________   __________   __________   __________   ________
--        /  _______/  /  ____   /  /  _______/  /  _______/  /  ____  \
--       /  / _____   /  /   /  /  /  /______   /  /______   /  /___/  /
--      /  / /_   /  /  /   /  /  /  _______/  /  _______/  /  __   __/
--     /  /___/  /  /  /___/  /  /  /         /  /______   /  /  \  \
--    /_________/  /_________/  /__/         /_________/  /__/    \__\
--
--    Functional programming environment, Version 2.21
--    Copyright Mark P Jones 1991.
--
--    Standard prelude for use of overloaded values using type classes.
--    Based on the Haskell standard prelude version 1.1.

help = "press :? for a list of commands"

-- Operator precedence table: -----------------------------------------------

infixl 9 !!
infixr 9 .
infixr 8 ^
infixl 7 *
infix  7 /, `div`, `rem`, `mod`
infixl 6 +, -
infix  5 \\
infixr 5 ++, :
infix  4 ==, /=, <, <=, >=, >
infix  4 `elem`, `notElem`
infixr 3 &&
infixr 2 ||

-- Standard combinators: ----------------------------------------------------

primitive strict "primStrict" :: (a -> b) -> a -> b

const          :: a -> b -> a
const k x       = k

id             :: a -> a
id    x         = x

curry          :: ((a,b) -> c) -> a -> b -> c
curry f a b     =  f (a,b)

uncurry        :: (a -> b -> c) -> (a,b) -> c
uncurry f (a,b) = f a b

fst            :: (a,b) -> a
fst (x,_)       = x

snd            :: (a,b) -> b
snd (_,y)       = y

fst3           :: (a,b,c) -> a
fst3 (x,_,_)    = x

snd3           :: (a,b,c) -> b
snd3 (_,x,_)    = x

thd3           :: (a,b,c) -> c
thd3 (_,_,x)    = x

(.)           :: (b -> c) -> (a -> b) -> (a -> c)
(f . g) x       = f (g x)

flip           :: (a -> b -> c) -> b -> a -> c
flip  f x y     = f y x

-- Boolean functions: -------------------------------------------------------

(&&), (||)     :: Bool -> Bool -> Bool
False && x      = False
True  && x      = x

False || x      = x
True  || x      = True

not            :: Bool -> Bool
not True        = False
not False       = True

and, or        :: [Bool] -> Bool
and             = foldr (&&) True
or              = foldr (||) False

any, all       :: (a -> Bool) -> [a] -> Bool
any p           = or  . map p
all p           = and . map p

otherwise      :: Bool
otherwise       = True

-- Character functions: -----------------------------------------------------

primitive ord "primCharToInt" :: Char -> Int
primitive chr "primIntToChar" :: Int -> Char


isAscii, isControl, isPrint, isSpace            :: Char -> Bool
isUpper, isLower, isAlpha, isDigit, isAlphanum  :: Char -> Bool

isAscii c     =  ord c < 128

isControl c   =  c < ' '    ||  c == '\DEL'

isPrint c     =  c >= ' '   &&  c <= '~'

isSpace c     =  c == ' '   || c == '\t'  || c == '\n'  || c == '\r'  ||
                               c == '\f'  || c == '\v'

isUpper c     =  c >= 'A'   &&  c <= 'Z'
isLower c     =  c >= 'a'   &&  c <= 'z'

isAlpha c     =  isUpper c  ||  isLower c
isDigit c     =  c >= '0'   &&  c <= '9'
isAlphanum c  =  isAlpha c  ||  isDigit c


toUpper, toLower      :: Char -> Char

toUpper c | isLower c  = chr (ord c - ord 'a' + ord 'A')
          | otherwise  = c

toLower c | isUpper c  = chr (ord c - ord 'A' + ord 'a')
          | otherwise  = c

-- Standard type classes: ---------------------------------------------------

class Eq a where
    (==), (/=) :: a -> a -> Bool
    x /= y      = not (x == y)

class Eq a => Ord a where
    (<), (<=), (>), (>=) :: a -> a -> Bool
    max, min             :: a -> a -> a

    x <  y            = x <= y && x /= y
    x >= y            = y <= x
    x >  y            = y < x

    max x y | x >= y  = x
            | y >= x  = y
    min x y | x <= y  = x
            | y <= x  = y

class Ord a => Ix a where
    range   :: (a,a) -> [a]
    index   :: (a,a) -> a -> Int
    inRange :: (a,a) -> a -> Bool

class Ord a => Enum a where
    enumFrom       :: a -> [a]              -- [n..]
    enumFromThen   :: a -> a -> [a]         -- [n,m..]
    enumFromTo     :: a -> a -> [a]         -- [n..m]
    enumFromThenTo :: a -> a -> a -> [a]    -- [n,n'..m]

    enumFromTo n m        = takeWhile (m>=) (enumFrom n)
    enumFromThenTo n n' m = takeWhile ((if n'>=n then (>=) else (<=)) m)
                                      (enumFromThen n n')

class Eq a => Num a where               -- simplified numeric class
    (+), (-), (*), (/) :: a -> a -> a
    negate             :: a -> a
    fromInteger           :: Int -> a

-- Type class instances: ----------------------------------------------------

primitive primEqInt    "primEqInt",
      primLeInt    "primLeInt"   :: Int -> Int -> Bool
primitive primPlusInt  "primPlusInt",
      primMinusInt "primMinusInt",
      primDivInt   "primDivInt",
      primMulInt   "primMulInt"  :: Int -> Int -> Int
primitive primNegInt   "primNegInt"  :: Int -> Int

instance Eq Int  where (==) = primEqInt

instance Ord Int where (<=) = primLeInt

instance Ix Int where
    range (m,n)      = [m..n]
    index (m,n) i    = i - m
    inRange (m,n) i  = m <= i && i <= n

instance Enum Int where
    enumFrom n       = iterate (1+) n
    enumFromThen n m = iterate ((m-n)+) n

instance Num Int where
    (+)           = primPlusInt
    (-)           = primMinusInt
    (*)           = primMulInt
    (/)           = primDivInt
    negate        = primNegInt
    fromInteger x = x

{- PC version off -}
primitive primEqFloat    "primEqFloat",
          primLeFloat    "primLeFloat"    :: Float -> Float -> Bool
primitive primPlusFloat  "primPlusFloat",
          primMinusFloat "primMinusFloat",
          primDivFloat   "primDivFloat",
          primMulFloat   "primMulFloat"   :: Float -> Float -> Float
primitive primNegFloat   "primNegFloat"   :: Float -> Float
primitive primIntToFloat "primIntToFloat" :: Int -> Float

instance Eq Float where (==) = primEqFloat

instance Ord Float where (<=) = primLeFloat

instance Enum Float where
    enumFrom n       = iterate (1.0+) n
    enumFromThen n m = iterate ((m-n)+) n

instance Num Float where
    (+)         = primPlusFloat
    (-)         = primMinusFloat
    (*)         = primMulFloat
    (/)         = primDivFloat
    negate      = primNegFloat
    fromInteger = primIntToFloat
{- PC version on -}

instance Eq Char where c == d  =  ord c == ord d

instance Ord Char where c <= d  =  ord c <= ord d

instance Ix Char where
    range (c,c')      = [c..c']
    index (c,c') ci   = ord ci - ord c
    inRange (c,c') ci = ord c <= i && i <= ord c' where i = ord ci

instance Enum Char where
    enumFrom c        = map chr [ord c ..]
    enumFromThen c c' = map chr [ord c, ord c' ..]

instance Eq a => Eq [a] where
    []     == []     =  True
    []     == (y:ys) =  False
    (x:xs) == []     =  False
    (x:xs) == (y:ys) =  x==y && xs==ys

instance Ord a => Ord [a] where
    []     <= _      =  True
    (_:_)  <= []     =  False
    (x:xs) <= (y:ys) =  x<y || (x==y && xs<=ys)

instance (Eq a, Eq b) => Eq (a,b) where
    (x,y) == (u,v)  =  x==u && y==v

instance (Ord a, Ord b) => Ord (a,b) where
    (x,y) <= (u,v)  = x<u  ||  (x==u && y<=v)

instance Eq Bool where
    True  == True   =  True
    False == False  =  True
    _     == _      =  False

-- Standard numerical functions: --------------------------------------------

primitive div    "primDivInt",
          rem    "primRemInt",
          mod    "primModInt"    :: Int -> Int -> Int

subtract  :: Num a => a -> a -> a
subtract   = flip (-)

even, odd :: Int -> Bool
even x     = x `rem` 2 == 0
odd        = not . even

gcd       :: Int -> Int -> Int
gcd x y    = gcd' (abs x) (abs y)
             where gcd' x 0 = x
                   gcd' x y = gcd' y (x `rem` y)

lcm       :: Int -> Int -> Int
lcm _ 0    = 0
lcm 0 _    = 0
lcm x y    = abs ((x `div` gcd x y) * y)

(^)       :: Int -> Int -> Int
x ^ 0      = 1
x ^ (n+1)  = f x n x
             where f _ 0 y = y
                   f x n y = g x n where
                             g x n | even n    = g (x*x) (n`div`2)
                                   | otherwise = f x (n-1) (x*y)

abs :: Int -> Int
abs x    | x >= 0  = x
         | x <  0  = - x

signum :: Int -> Int
signum x | x == 0  = 0
         | x > 0   = 1
         | x < 0   = -1

sum, product    :: [Int] -> Int
sum              = foldl' (+) 0
product          = foldl' (*) 1

sums, products    :: [Int] -> [Int]
sums             = scanl (+) 0
products         = scanl (*) 1

-- Standard list processing functions: --------------------------------------

head             :: [a] -> a
head (x:_)        = x

last             :: [a] -> a
last [x]          = x
last (_:xs)       = last xs

tail             :: [a] -> [a]
tail (_:xs)       = xs

init             :: [a] -> [a]
init [x]          = []
init (x:xs)       = x : init xs

(++)             :: [a] -> [a] -> [a]    -- append lists.  Associative with
[]     ++ ys      = ys                   -- left and right identity [].
(x:xs) ++ ys      = x:(xs++ys)

length         :: [a] -> Int           -- calculate length of list
length            = foldl' (\n _ -> n+1) 0

(!!)             :: [a] -> Int -> a      -- xs!!n selects the nth element of
(x:_)  !! 0       = x                    -- the list xs (first element xs!!0)
(_:xs) !! (n+1)   = xs !! n              -- for any n < length xs.

iterate          :: (a -> a) -> a -> [a] -- generate the infinite list
iterate f x       = x : iterate f (f x)  -- [x, f x, f (f x), ...

repeat           :: a -> [a]             -- generate the infinite list
repeat x          = xs where xs = x:xs   -- [x, x, x, x, ...

cycle            :: [a] -> [a]           -- generate the infinite list
cycle xs          = xs' where xs'=xs++xs'-- xs ++ xs ++ xs ++ ...

copy             :: Int -> a -> [a]      -- make list of n copies of x
copy n x          = take n xs where xs = x:xs

nub              :: Eq a => [a] -> [a]   -- remove duplicates from list
nub []            = []
nub (x:xs)        = x : nub (filter (x/=) xs)

reverse          :: [a] -> [a]           -- reverse elements of list
reverse           = foldl (flip (:)) []

elem, notElem    :: Eq a => a -> [a] -> Bool
elem              = any . (==)           -- test for membership in list
notElem           = all . (/=)           -- test for non-membership

maximum, minimum :: Ord a => [a] -> a
maximum           = foldl1 max          -- max element in non-empty list
minimum           = foldl1 min          -- min element in non-empty list

concat           :: [[a]] -> [a]        -- concatenate list of lists
concat            = foldr (++) []

transpose        :: [[a]] -> [[a]]      -- transpose list of lists
transpose         = foldr
                      (\xs xss -> zipWith (:) xs (xss ++ repeat []))
                      []

-- null provides a simple and efficient way of determining whether a given
-- list is empty, without using (==) and hence avoiding a constraint of the
-- form Eq [a].

null             :: [a] -> Bool
null []           = True
null (_:_)        = False

-- (\\) is used to remove the first occurrence of each element in the second
-- list from the first list.  It is a kind of inverse of (++) in the sense
-- that  (xs ++ ys) \\ xs = ys for any finite list xs of proper values xs.

(\\)             :: Eq a => [a] -> [a] -> [a]
(\\)              = foldl del
                    where []     `del` _  = []
                          (x:xs) `del` y
                             | x == y     = xs
                             | otherwise  = x : xs `del` y


-- map f xs applies the function f to each element of the list xs returning
-- the corresponding list of results.  filter p xs returns the sublist of xs
-- containing those elements which satisfy the predicate p.

map              :: (a -> b) -> [a] -> [b]
map f []          = []
map f (x:xs)      = f x : map f xs

filter           :: (a -> Bool) -> [a] -> [a]
filter _ []       = []
filter p (x:xs)
    | p x         = x : xs'
    | otherwise   = xs'
                  where xs' = filter p xs

-- Fold primitives:  The foldl and scanl functions, variants foldl1 and
-- scanl1 for non-empty lists, and strict variants foldl' scanl' describe
-- common patterns of recursion over lists.  Informally:
--
--  foldl f a [x1, x2, ..., xn]  = f (...(f (f a x1) x2)...) xn
--                               = (...((a `f` x1) `f` x2)...) `f` xn
-- etc...
--
-- The functions foldr, scanr and variants foldr1, scanr1 are duals of these
-- functions:
-- e.g.  foldr f a xs = foldl (flip f) a (reverse xs)  for finite lists xs.

foldl            :: (a -> b -> a) -> a -> [b] -> a
foldl f z []      = z
foldl f z (x:xs)  = foldl f (f z x) xs

foldl1           :: (a -> a -> a) -> [a] -> a
foldl1 f (x:xs)   = foldl f x xs

foldl'           :: (a -> b -> a) -> a -> [b] -> a
foldl' f a []     =  a
foldl' f a (x:xs) =  strict (foldl' f) (f a x) xs

scanl            :: (a -> b -> a) -> a -> [b] -> [a]
scanl f q xs      = q : (case xs of
                         []   -> []
                         x:xs -> scanl f (f q x) xs)

scanl1           :: (a -> a -> a) -> [a] -> [a]
scanl1 f (x:xs)   = scanl f x xs

scanl'           :: (a -> b -> a) -> a -> [b] -> [a]
scanl' f q xs     = q : (case xs of
                         []   -> []
                         x:xs -> strict (scanl' f) (f q x) xs)

foldr            :: (a -> b -> b) -> b -> [a] -> b
foldr f z []      = z
foldr f z (x:xs)  = f x (foldr f z xs)

foldr1           :: (a -> a -> a) -> [a] -> a
foldr1 f [x]      = x
foldr1 f (x:xs)   = f x (foldr1 f xs)

scanr            :: (a -> b -> b) -> b -> [a] -> [b]
scanr f q0 []     = [q0]
scanr f q0 (x:xs) = f x q : qs
                    where qs@(q:_) = scanr f q0 xs

scanr1           :: (a -> a -> a) -> [a] -> [a]
scanr1 f [x]      = [x]
scanr1 f (x:xs)   = f x q : qs
                    where qs@(q:_) = scanr1 f xs

-- List breaking functions:
--
--   take n xs       returns the first n elements of xs
--   drop n xs       returns the remaining elements of xs
--   splitAt n xs    = (take n xs, drop n xs)
--
--   takeWhile p xs  returns the longest initial segment of xs whose
--                   elements satisfy p
--   dropWhile p xs  returns the remaining portion of the list
--   span p xs       = (takeWhile p xs, dropWhile p xs)
--
--   takeUntil p xs  returns the list of elements upto and including the
--                   first element of xs which satisfies p

take                :: Int -> [a] -> [a]
take 0     _         = []
take _     []        = []
take (n+1) (x:xs)    = x : take n xs

drop                :: Int -> [a] -> [a]
drop 0     xs        = xs
drop _     []        = []
drop (n+1) (_:xs)    = drop n xs

splitAt             :: Int -> [a] -> ([a], [a])
splitAt 0     xs     = ([],xs)
splitAt _     []     = ([],[])
splitAt (n+1) (x:xs) = (x:xs',xs'') where (xs',xs'') = splitAt n xs

takeWhile           :: (a -> Bool) -> [a] -> [a]
takeWhile p []       = []
takeWhile p (x:xs)
         | p x       = x : takeWhile p xs
         | otherwise = []

takeUntil           :: (a -> Bool) -> [a] -> [a]
takeUntil p []       = []
takeUntil p (x:xs)
       | p x         = [x]
       | otherwise   = x : takeUntil p xs

dropWhile           :: (a -> Bool) -> [a] -> [a]
dropWhile p []       = []
dropWhile p xs@(x:xs')
         | p x       = dropWhile p xs'
         | otherwise = xs

span, break         :: (a -> Bool) -> [a] -> ([a],[a])
span p []            = ([],[])
span p xs@(x:xs')
         | p x       = let (ys,zs) = span p xs' in (x:ys,zs)
         | otherwise = ([],xs)
break p              = span (not . p)

-- Text processing:
--   lines s     returns the list of lines in the string s.
--   words s     returns the list of words in the string s.
--   unlines ls  joins the list of lines ls into a single string
--               with lines separated by newline characters.
--   unwords ws  joins the list of words ws into a single string
--               with words separated by spaces.

lines     :: String -> [String]
lines ""   = []
lines s    = l : (if null s' then [] else lines (tail s'))
             where (l, s') = break ('\n'==) s

words     :: String -> [String]
words s    = case dropWhile isSpace s of
                  "" -> []
                  s' -> w : words s''
                        where (w,s'') = break isSpace s'

unlines   :: [String] -> String
unlines    = concat . map (\l -> l ++ "\n")

unwords   :: [String] -> String
unwords [] = []
unwords ws = foldr1 (\w s -> w ++ ' ':s) ws

-- Merging and sorting lists:

merge               :: Ord a => [a] -> [a] -> [a]
merge []     ys      = ys
merge xs     []      = xs
merge (x:xs) (y:ys)
        | x <= y     = x : merge xs (y:ys)
        | otherwise  = y : merge (x:xs) ys

sort                :: Ord a => [a] -> [a]
sort                 = foldr insert []

insert              :: Ord a => a -> [a] -> [a]
insert x []          = [x]
insert x (y:ys)
        | x <= y     = x:y:ys
        | otherwise  = y:insert x ys

qsort               :: Ord a => [a] -> [a]
qsort []             = []
qsort (x:xs)         = qsort [ u | u<-xs, u<x ] ++
                             [ x ] ++
                       qsort [ u | u<-xs, u>=x ]

-- zip and zipWith families of functions:

zip  :: [a] -> [b] -> [(a,b)]
zip   = zipWith  (\a b -> (a,b))

zip3 :: [a] -> [b] -> [c] -> [(a,b,c)]
zip3  = zipWith3 (\a b c -> (a,b,c))

zip4 :: [a] -> [b] -> [c] -> [d] -> [(a,b,c,d)]
zip4  = zipWith4 (\a b c d -> (a,b,c,d))

zip5 :: [a] -> [b] -> [c] -> [d] -> [e] -> [(a,b,c,d,e)]
zip5  = zipWith5 (\a b c d e -> (a,b,c,d,e))

zip6 :: [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [(a,b,c,d,e,f)]
zip6  = zipWith6 (\a b c d e f -> (a,b,c,d,e,f))

zip7 :: [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [g] -> [(a,b,c,d,e,f,g)]
zip7  = zipWith7 (\a b c d e f g -> (a,b,c,d,e,f,g))


zipWith                  :: (a->b->c) -> [a]->[b]->[c]
zipWith z (a:as) (b:bs)   = z a b : zipWith z as bs
zipWith _ _      _        = []

zipWith3                 :: (a->b->c->d) -> [a]->[b]->[c]->[d]
zipWith3 z (a:as) (b:bs) (c:cs)
                          = z a b c : zipWith3 z as bs cs
zipWith3 _ _ _ _          = []

zipWith4                 :: (a->b->c->d->e) -> [a]->[b]->[c]->[d]->[e]
zipWith4 z (a:as) (b:bs) (c:cs) (d:ds)
                          = z a b c d : zipWith4 z as bs cs ds
zipWith4 _ _ _ _ _        = []

zipWith5                 :: (a->b->c->d->e->f) -> [a]->[b]->[c]->[d]->[e]->[f]
zipWith5 z (a:as) (b:bs) (c:cs) (d:ds) (e:es)
                          = z a b c d e : zipWith5 z as bs cs ds es
zipWith5 _ _ _ _ _ _      = []

zipWith6                 :: (a->b->c->d->e->f->g)
                            -> [a]->[b]->[c]->[d]->[e]->[f]->[g]
zipWith6 z (a:as) (b:bs) (c:cs) (d:ds) (e:es) (f:fs)
                          = z a b c d e f : zipWith6 z as bs cs ds es fs
zipWith6 _ _ _ _ _ _ _    = []

zipWith7                 :: (a->b->c->d->e->f->g->h)
                             -> [a]->[b]->[c]->[d]->[e]->[f]->[g]->[h]
zipWith7 z (a:as) (b:bs) (c:cs) (d:ds) (e:es) (f:fs) (g:gs)
                          = z a b c d e f g : zipWith7 z as bs cs ds es fs gs
zipWith7 _ _ _ _ _ _ _ _  = []

-- Formatted output: --------------------------------------------------------

primitive primPrint "primPrint"  :: Int -> a -> String -> String

show'       :: a -> String
show' x      = primPrint 0 x []

cjustify, ljustify, rjustify :: Int -> String -> String

cjustify n s = space halfm ++ s ++ space (m - halfm)
               where m     = n - length s
                     halfm = m `div` 2
ljustify n s = s ++ space (n - length s)
rjustify n s = space (n - length s) ++ s

space       :: Int -> String
space n      = copy n ' '

layn        :: [String] -> String
layn         = lay 1 where lay _ []     = []
                           lay n (x:xs) = rjustify 4 (show n) ++ ") "
                                           ++ x ++ "\n" ++ lay (n+1) xs

-- Miscellaneous: -----------------------------------------------------------

until                  :: (a -> Bool) -> (a -> a) -> a -> a
until p f x | p x       = x
            | otherwise = until p f (f x)

until'                 :: (a -> Bool) -> (a -> a) -> a -> [a]
until' p f              = takeUntil p . iterate f

error                  :: String -> a
error msg | False       = error msg

undefined              :: a
undefined | False       = undefined

asTypeOf               :: a -> a -> a
x `asTypeOf` _          = x

-- A trimmed down version of the Haskell Text class: ------------------------

type  ShowS   = String -> String

class Text a where
    showsPrec      :: Int -> a -> ShowS
    showList       :: [a] -> ShowS

    showsPrec       = primPrint
    showList []     = showString "[]"
    showList (x:xs) = showChar '[' . shows x . showl xs
                      where showl []     = showChar ']'
                            showl (x:xs) = showChar ',' . shows x . showl xs

shows      :: Text a => a -> ShowS
shows       =  showsPrec 0

show       :: Text a => a -> String
show x      =  shows x ""

showChar   :: Char -> ShowS
showChar    =  (:)

showString :: String -> ShowS
showString  =  (++)

instance Text ()

instance Text Int

{- PC version off -}
instance Text Float
{- PC version on -}

instance Text Char where
    showList cs = showChar '"' . showl cs
                  where showl ""       = showChar '"'
                        showl ('"':cs) = showString "\\\"" . showl cs
                        showl (c:cs)   = showChar c . showl cs
            -- Haskell has   showLitChar c . showl cs

instance Text a => Text [a]  where
    showsPrec p = showList

instance (Text a, Text b) => Text (a,b) where
    showsPrec p (x,y) = showChar '(' . shows x . showChar ',' .
                                       shows y . showChar ')'

-- I/O functions and definitions: -------------------------------------------

stdin         =  "stdin"
stdout        =  "stdout"
stderr        =  "stderr"
stdecho       =  "stdecho"

data Request  =  -- file system requests:
                ReadFile      String
              | WriteFile     String String
              | AppendFile    String String
                 -- channel system requests:
              | ReadChan      String
              | AppendChan    String String
                 -- environment requests:
              | Echo          Bool

data Response = Success
              | Str String
              | Failure IOError

data IOError  = WriteError   String
              | ReadError    String
              | SearchError  String
              | FormatError  String
              | OtherError   String

type Dialogue  =  [Response] -> [Request]
type SuccCont  =                Dialogue
type StrCont   =  String     -> Dialogue
type FailCont  =  IOError    -> Dialogue

done          ::                                                Dialogue
readFile      :: String ->           FailCont -> StrCont     -> Dialogue
writeFile     :: String -> String -> FailCont -> SuccCont    -> Dialogue
appendFile    :: String -> String -> FailCont -> SuccCont    -> Dialogue
readChan      :: String ->           FailCont -> StrCont     -> Dialogue
appendChan    :: String -> String -> FailCont -> SuccCont    -> Dialogue
echo          :: Bool ->             FailCont -> SuccCont    -> Dialogue

done resps    =  []
readFile name fail succ resps =
     (ReadFile name) : strDispatch fail succ resps
writeFile name contents fail succ resps =
    (WriteFile name contents) : succDispatch fail succ resps
appendFile name contents fail succ resps =
    (AppendFile name contents) : succDispatch fail succ resps
readChan name fail succ resps =
    (ReadChan name) : strDispatch fail succ resps
appendChan name contents fail succ resps =
    (AppendChan name contents) : succDispatch fail succ resps
echo bool fail succ resps =
    (Echo bool) : succDispatch fail succ resps

strDispatch fail succ (resp:resps) =
            case resp of Str val     -> succ val resps
                         Failure msg -> fail msg resps

succDispatch fail succ (resp:resps) =
            case resp of Success     -> succ resps
                         Failure msg -> fail msg resps

abort           :: FailCont
abort err        = done

exit            :: FailCont
exit err         = appendChan stdout msg abort done
                   where msg = case err of ReadError s   -> s
                                           WriteError s  -> s
                                           SearchError s -> s
                                           FormatError s -> s
                                           OtherError s  -> s

print           :: Text a => a -> Dialogue
print x          = appendChan stdout (show x) abort done

prints          :: Text a => a -> String -> Dialogue
prints x s       = appendChan stdout (shows x s) abort done

interact    :: (String -> String) -> Dialogue
interact f     = readChan stdin abort
                (\x -> appendChan stdout (f x) abort done)

run        :: (String -> String) -> Dialogue
run f         = echo False abort (interact f)

-- End of Gofer standard prelude: --------------------------------------------