Lens.Micro.FieldN

Gives access to the 1st field of a tuple (up to 5-tuples).

Getting the 1st component:

>>> (1,2,3,4,5) ^. _11

Setting the 1st component:

>>> (1,2,3) & _1 .~ 10(10,2,3)

Note that this lens is lazy, and can set fields even of undefined:

>>> set _1 10 undefined :: (Int, Int)(10,*** Exception: Prelude.undefined

This is done to avoid violating a lens law stating that you can get back what you put:

>>> view _1 . set _1 10 $ (undefined :: (Int, Int))10

The implementation (for 2-tuples) is:

_1 f t = (,) <$> f    (fst t)
             <*> pure (snd t)

or, alternatively,

_1 f ~(a,b) = (\a' -> (a',b)) <$> f a

(where ~ means a lazy pattern).

_2, _3, _4, and _5 are also available (see below).