36 lines
1.4 KiB
Org Mode
36 lines
1.4 KiB
Org Mode
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:PROPERTIES:
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:ID: 10eb4672-19ab-4275-a110-5446c96e7e24
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:END:
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#+title: Applicative
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In [[id:9e68d422-cced-4177-96d1-90f777b9a493][Software Development]], this refers to a [[id:7a19b34d-c4bb-462b-8fae-581bf06dfdc4][Functor]] that provides a method for
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applying a function wrapped in such a type to a value wrapped in the same type.
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In [[id:9ac78677-2602-4a06-af0a-4ed82e98a9b6][Haskell]], the function for applying a wrapped function to a value wrapped in
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the same type is available as the infix operator =<*>=, and facilitates the
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application of a function taking an arbitrary number of arguments over multiple
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wrapped values. An applicative must also implement the =pure= function, which
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takes a single argument and returns it wrapped.
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#+caption: Applicative functions in Haskell
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#+begin_src haskell :exports code
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pure :: Applicative f => a -> f a
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(<*>) :: Applicative f => f (a -> b) -> f a -> f b
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#+end_src
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In the following example, =fmap= (=<$>=) first applies the =add= function to the
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value =Just 1=, resulting in a function of the type =Just (Int -> Int)=. The
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applicative infix operator (=<*>=) then applies that function to the remaining
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value =Just 2=, resulting in =Just 3=.
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#+caption: Applying a function over multiple wrapped values
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#+begin_src haskell :cache yes :exports both
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add :: Int -> Int -> Int
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add x y = x + y
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add <$> Just 1 <*> Just 2
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#+end_src
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#+RESULTS[10751e7c3100f27569974ee18b3f34498166dfc5]:
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: Prelude> Just 3
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