How do I concatenate two Snoc lists?
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13-07-2021 - |
Question
I have to construct a Snoc list, the reverse of Cons. I've done to add one element forward i don't know how to concatenate two lists. That's the situation now:
module Tsil where
data Tsil a = Lin
| Snoc (Tsil a, a)
deriving (Eq, Ord, Show, Read)
empty :: Tsil a
empty = Lin
infixr 2 |:
(|:) :: a -> Tsil a -> Tsil a
(|:) a t = Snoc (t, a)
infixr 5 |++
(|++) :: Tsil a -> Tsil a -> Tsil a
(|++) a Lin = a
(|++) Lin a = a
Solution
Your list type is the same as Haskell's, so just make it a Haskell list, concatenate, convert back. Hooray for reusability in Haskell ;-)
toList Lin = []
toList (Snoc (xs, x)) = x : toList xs
toTsil [] = Lin
toTsil (x:xs) = Snoc (toTsil xs, x)
a (|++) b = toTsil $ toList a ++ toList b
OTHER TIPS
(|++) l (Snoc (t,x)) = Snoc (l |++ t,x)
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