A
Traversal reading and writing to the
tail of a
non-empty container.
>>> [a,b] & _tail .~ [c,d,e]
[a,c,d,e]
>>> [] & _tail .~ [a,b]
[]
>>> [a,b,c,d,e] & _tail.traverse %~ f
[a,f b,f c,f d,f e]
>>> [1,2] & _tail .~ [3,4,5]
[1,3,4,5]
>>> [] & _tail .~ [1,2]
[]
>>> [a,b,c]^?_tail
Just [b,c]
>>> [1,2]^?!_tail
[2]
>>> "hello"^._tail
"ello"
>>> ""^._tail
""
This isn't limited to lists. For instance you can also
traverse
the tail of a
Seq.
>>> Seq.fromList [a,b] & _tail .~ Seq.fromList [c,d,e]
fromList [a,c,d,e]
>>> Seq.fromList [a,b,c] ^? _tail
Just (fromList [b,c])
>>> Seq.fromList [] ^? _tail
Nothing
_tail :: Traversal' [a] [a]
_tail :: Traversal' (Seq a) (Seq a)
_tail :: Traversal' (Vector a) (Vector a)