List comprehensions: Difference between revisions
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(→JS ES6: Added an alternative expression of list comprehensions, in terms of bind (>>=)) |
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enumFromTo(1, n)); |
enumFromTo(1, n)); |
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})(20);</lang> |
})(20);</lang> |
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Or, expressed in terms of bind (>>=) |
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<lang Javascript>(n => { |
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'use strict'; |
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// GENERIC FUNCTIONS ------------------------------------------------------ |
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// bind (>>=) :: Monad m => m a -> (a -> m b) -> m b |
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const bind = (m, mf) => |
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Array.isArray(m) ? ( |
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bindList(m, mf) |
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) : bindMay(m, mf); |
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// bindList (>>=) :: [a] -> (a -> [b]) -> [b] |
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const bindList = (xs, mf) => [].concat.apply([], xs.map(mf)); |
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// enumFromTo :: Enum a => a -> a -> [a] |
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const enumFromTo = (m, n) => |
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(typeof m !== 'number' ? ( |
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enumFromToChar |
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) : enumFromToInt) |
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.apply(null, [m, n]); |
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// enumFromToInt :: Int -> Int -> [Int] |
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const enumFromToInt = (m, n) => |
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Array.from({ |
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length: Math.floor(n - m) + 1 |
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}, (_, i) => m + i); |
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// EXAMPLE ---------------------------------------------------------------- |
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// [(x, y, z) | x <- [1..n], y <- [x..n], z <- [y..n], x ^ 2 + y ^ 2 == z ^ 2] |
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return bind(enumFromTo(1, n), |
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x => bind(enumFromTo(x, n), |
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y => bind(enumFromTo(y, n), |
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z => x * x + y * y === z * z ? [ |
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[x, y, z] |
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] : [] |
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))); |
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})(20);</lang> |
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{{Out}} |
{{Out}} |
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<lang JavaScript>[[3, 4, 5], [5, 12, 13], [6, 8, 10], [8, 15, 17], [9, 12, 15], [12, 16, 20]]</lang> |
<lang JavaScript>[[3, 4, 5], [5, 12, 13], [6, 8, 10], [8, 15, 17], [9, 12, 15], [12, 16, 20]]</lang> |
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