[Haskell-cafe] function unique

[Hugh Perkins]

Simple answer: you always have to have the single element first, then the
list bit second.  It's just the way it is.  You can learn why later on ;-)

On 7/11/07, Alexteslin <alexteslin at yahoo.co.uk> wrote:
>
>
> Oh, I am lost now - for now anyway.
> I am attempting to do next exercise in the book to define reverse function
> using primitive recursion and pattern matching on lists.  But getting
> stack
> because when i con in front of xs (xs:x) i get en error, which i thought i
> would be getting anyway.  I tried to define a helper function and cons
> there
> in front of xs and i get type errors again.
>
> I know these are easy and boring questions but i would appreciate a hint.
>
> Thank you
>
>
> Neil Mitchell wrote:
> >
> > Hi
> >
> >> unique = unique' []
> >>
> >> unique' _ [] = []
> >> unique' history (x:xs) = if x `elem` history
> >>   then next
> >>   else (x:next) where next = (uniq' (x:hist) xs)
> >
> > You can express this more neatly:
> >
> > unique' _ [] = []
> > unique' history (x:xs) = [x | x `notElem` history] ++ unique'
> (x:history)
> > xs
> >
> > Thanks
> >
> > Neil
> > _______________________________________________
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> > http://www.haskell.org/mailman/listinfo/haskell-cafe
> >
> >
>
> --
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> http://www.nabble.com/function-unique-tf4058328.html#a11547781
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