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Create a list containing all integers within a given range.
range x y = [x..y]
range = enumFromTo
range x y = take (y-x+1) $ iterate (+1) x
range start stop | start > stop = reverse (range stop start) | start == stop = [stop] | start < stop = start:range (start+1) stop
The following does the same but without using a reverse function
range :: Int -> Int -> [Int] range n m | n == m = [n] | n < m = n:(range (n+1) m) | n > m = n:(range (n-1) m)
or, a generic and shorter version of the above
range :: (Ord a, Enum a) => a -> a -> [a] range a b | (a == b) = [a] range a b = a:range ((if a < b then succ else pred) a) b
or with scanl
range l r = scanl (+) l (replicate (l - r) 1)
with support for both directions
range l r = scanl op l $ replicate diff 1 where op = if l < r then (+) else (-) diff = abs $ l - r
Since there's already syntactic sugar for ranges, there's usually no reason to define a function like 'range' in Haskell. In fact, the syntactic sugar is implemented using the enumFromTo function, which is exactly what 'range' should be.