Difference between revisions of "99 questions/Solutions/22"
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m (This edit provides another method of computing the range without using reverse) |
The swerve (talk | contribs) (another scanl example) |
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| n < m = n:(range (n+1) m) |
| n < m = n:(range (n+1) m) |
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| n > m = n:(range (n-1) m) |
| n > m = n:(range (n-1) m) |
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+ | </haskell> |
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+ | or, a generic and shorter version of the above |
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+ | <haskell> |
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+ | range :: (Ord a, Enum a) => a -> a -> [a] |
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+ | range a b | (a == b) = [a] |
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+ | range a b = a:range ((if a < b then succ else pred) a) b |
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+ | </haskell> |
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+ | or with scanl |
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+ | <haskell> |
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+ | range l r = scanl (+) l (replicate (l - r) 1) |
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+ | </haskell> |
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+ | with support for both directions |
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+ | <haskell> |
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+ | range l r = scanl op l $ replicate diff 1 |
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+ | where |
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+ | op = if l < r then (+) else (-) |
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+ | diff = abs $ l - r |
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</haskell> |
</haskell> |
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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. |
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. |
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+ | |||
+ | [[Category:Programming exercise spoilers]] |
Latest revision as of 02:08, 5 April 2014
Create a list containing all integers within a given range.
range x y = [x..y]
or
range = enumFromTo
or
range x y = take (y-x+1) $ iterate (+1) x
or
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.