polyvariadic | 易学教程

Haskell, polyvariadic function and type inference

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问题 While looking for Polyvariadic function examples, I found this resource: StackOverflow: How to create a polyvariadic haskell function?, and there was an answer snippet like this: class SumRes r where sumOf :: Integer -> r instance SumRes Integer where sumOf = id instance (Integral a, SumRes r) => SumRes (a -> r) where sumOf x = sumOf . (x +) . toInteger Then we could use: *Main> sumOf 1 :: Integer 1 *Main> sumOf 1 4 7 10 :: Integer 22 *Main> sumOf 1 4 7 10 0 0 :: Integer 22 *Main> sumOf 1 4 7

How does Haskell printf work?

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Haskell's type safety is second to none only to dependently-typed languages. But there is some deep magic going on with Text.Printf that seems rather type-wonky. > printf "%d\n" 3 3 > printf "%s %f %d" "foo" 3.3 3 foo 3.3 3 What is the deep magic behind this? How can the Text.Printf.printf function take variadic arguments like this? What is the general technique used to allow for variadic arguments in Haskell, and how does it work? (Side note: some type safety is apparently lost when using this technique.) > :t printf "%d\n" "foo" printf "%d\n" "foo" :: (PrintfType ([Char] -> t)) => t The

How does Haskell printf work?

阅读更多关于 How does Haskell printf work?

问题 Haskell's type safety is second to none only to dependently-typed languages. But there is some deep magic going on with Text.Printf that seems rather type-wonky. > printf "%d\n" 3 3 > printf "%s %f %d" "foo" 3.3 3 foo 3.3 3 What is the deep magic behind this? How can the Text.Printf.printf function take variadic arguments like this? What is the general technique used to allow for variadic arguments in Haskell, and how does it work? (Side note: some type safety is apparently lost when using