Haskell Linked List Algebraic Datatype -


i attempting implement haskell algebraic datatype linked list (or perhaps more accurately linked list-like since don't know of way memory addressing using haskell) helper functions converting , haskell's naive list type , wrote following:

data linkedlist = nill | node (linkedlist a) deriving show  hlisttolinkedlist :: [a] -> linkedlist hlisttolinkedlist [] = nill hlisttolinkedlist x:[] = node x nill hlisttolinkedlist x:xs = node (x) (stringtolinkedlist xs)  linkedlisttohlist :: linkedlist char -> [char] linkedlisttohlist (node b) = ++ linkedlisttostring b linkedlisttohlist nill = ''

i following compiler error:

@5:1-5:21 parse error in pattern: hlisttolinkedlist

i'm not sure what's wrong function. please explain?

the minimal change needed make compile add parentheses patterns non-empty lists; e.g.

hlisttolinkedlist (x:xs) = ...

by requiring parentheses complex patterns, compiler need not know how many arguments each constructor takes; important trick reducing context sensitivity , promoting separate compilation.


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