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data ZipList a = ZL [a] a [a] deriving (Eq, Show)
 
test :: ZipList Int
test = ZL [3,2,1] 4 [5,6,7]
 
-- Create a new empty list and make e the default item that is
newZipList :: a -> ZipList a
newZipList x = ZL [] x []
 
-- Returns true if only one item present
-- i.e. the left and right lists are empty
isSingleton :: ZipList a -> Bool
isSingleton (ZL [] _ []) = True
isSingleton _            = False
 
-- Move the current item one place forwards in the list
after :: ZipList a -> ZipList a
after (ZL ls x [])     = ZL ls x [] -- Can't go any further right
after (ZL ls x (r:rs)) = ZL (x:ls) r rs
 
-- Move the current item one place backwards in the list
before :: ZipList a -> ZipList a
before (ZL [] x rs)     = ZL [] x rs -- Can't go any further left
before (ZL (l:ls) x rs) = ZL ls l (x:rs)
 

prog.c:1:1: error: unknown type name ‘data’
 data ZipList a = ZL [a] a [a] deriving (Eq, Show)
 ^~~~
prog.c:1:14: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘a’
 data ZipList a = ZL [a] a [a] deriving (Eq, Show)
              ^
prog.c:18:43: warning: missing terminating ' character
 after (ZL ls x [])     = ZL ls x [] -- Can't go any further right
                                           ^
prog.c:18:43: error: missing terminating ' character
 after (ZL ls x [])     = ZL ls x [] -- Can't go any further right
                                           ^~~~~~~~~~~~~~~~~~~~~~~
prog.c:23:44: warning: missing terminating ' character
 before (ZL [] x rs)     = ZL [] x rs -- Can't go any further left
                                            ^
prog.c:23:44: error: missing terminating ' character
 before (ZL [] x rs)     = ZL [] x rs -- Can't go any further left
                                            ^~~~~~~~~~~~~~~~~~~~~~

Standard output is empty