length xs > 15) (map chain [1..10...">
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Vaguely about this use of lambda

So, I think of Lambdas, as shown in "Learn You a Haskell":

(filter (\xs -> length xs > 15) (map chain [1..100]))

Input for xs is a list generated from (map chain [1..100])) This is fairly easy to read.

So, here, where I got confused, I look at some real world code (tm).

Here is the function from conduit

fmap f (ResourceT m) = ResourceT $ \r -> fmap f (m r)

Where is the input for r introduced?

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2 answers

rwill not matter until the function \r -> fmap f (m r)is called. In a definition, a fmapfunction is never called - it is stored only in ResourceT. Then it can be removed from ResourceTand called out. This is when it rgets the value.

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\r -> fmap f (m r) - , closure. f m , . , Haskell , , .

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