haskellapplicative# Applicative Functor - Haskell

`pure (+) <*> (Just 1) <*> (Just 2)`

Is the expansion of above expression is correct?

```
pure (+) <*> (Just 1) <*> (Just 2)
= (Just (+)) <*> (Just 1) <*> (Just 2)
= (Just (1+)) <*> (Just 2)
= Just 3
```

if so then why we can't do just this `(Just (+)) <*> (Just 2)`

?

Solution

I believe you have already answered your question in the comments. So just for the sake of completion...

`(Just (+)) <*> (Just 2)`

is a partially applied function that the REPL cannot print, giving the error:

`• No instance for (Show (Integer -> Integer)) arising from a use of ‘print’`

,

but otherwise it is fine.

No problem here:

`> :t (Just (+)) <*> (Just 2)`

`(Just (+)) <*> (Just 2) :: Num a => Maybe (a -> a)`

.

Completing the function is fine too:

`> f = (Just (+)) <*> (Just 2)`

`> f <*> Just 1`

`> Just 3`

Your understanding seems perfectly sound.

Incidentally, another way of writing this is:

`(+) <$> (Just 1) <*> (Just 2)`

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