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Last active May 7, 2017 14:34
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arrows.md

Arrows

Arrows are generalisations of Monads, which raise function composition into the type system using type-level functions. They're absolutely not examinable.

Amazingly, this is valid Haskell.

type T a b = a -> b
f = (\x -> show x) :: T Int String  -- this is a value -- not a function -- which represents the transformation of an Integer to a STring.
f 3 -- "3"

Notice that the type of f is a single value, with no currying, even though f does perform computation:

-- f :: T Int String

I don't understand Arrows, but I'm sure this is the beginning of them. Try it in ghci.

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