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1. _head :: Cons s s a a => Traversal' s a

   lens	Control.Lens.Combinators

   A Traversal reading and writing to the head of a non-empty container.

   >>> [a,b,c]^? _head
   Just a
   

   >>> [a,b,c] & _head .~ d
   [d,b,c]
   

   >>> [a,b,c] & _head %~ f
   [f a,b,c]
   

   >>> [] & _head %~ f
   []
   

   >>> [1,2,3]^?!_head
   1
   

   >>> []^?_head
   Nothing
   

   >>> [1,2]^?_head
   Just 1
   

   >>> [] & _head .~ 1
   []
   

   >>> [0] & _head .~ 2
   [2]
   

   >>> [0,1] & _head .~ 2
   [2,1]
   

   This isn't limited to lists. For instance you can also traverse the head of a Seq:

   >>> Seq.fromList [a,b,c,d] & _head %~ f
   fromList [f a,b,c,d]
   

   >>> Seq.fromList [] ^? _head
   Nothing
   

   >>> Seq.fromList [a,b,c,d] ^? _head
   Just a
   

   _head :: Traversal' [a] a
   _head :: Traversal' (Seq a) a
   _head :: Traversal' (Vector a) a
   

2. _head :: Cons s s a a => Traversal' s a

   lens	Control.Lens.Cons

   A Traversal reading and writing to the head of a non-empty container.

   >>> [a,b,c]^? _head
   Just a
   

   >>> [a,b,c] & _head .~ d
   [d,b,c]
   

   >>> [a,b,c] & _head %~ f
   [f a,b,c]
   

   >>> [] & _head %~ f
   []
   

   >>> [1,2,3]^?!_head
   1
   

   >>> []^?_head
   Nothing
   

   >>> [1,2]^?_head
   Just 1
   

   >>> [] & _head .~ 1
   []
   

   >>> [0] & _head .~ 2
   [2]
   

   >>> [0,1] & _head .~ 2
   [2,1]
   

   This isn't limited to lists. For instance you can also traverse the head of a Seq:

   >>> Seq.fromList [a,b,c,d] & _head %~ f
   fromList [f a,b,c,d]
   

   >>> Seq.fromList [] ^? _head
   Nothing
   

   >>> Seq.fromList [a,b,c,d] ^? _head
   Just a
   

   _head :: Traversal' [a] a
   _head :: Traversal' (Seq a) a
   _head :: Traversal' (Vector a) a
   

3. typeFamilyHeadInjectivityAnn :: Lens' TypeFamilyHead (Maybe InjectivityAnn)

   lens	Language.Haskell.TH.Lens

   No documentation available.

4. typeFamilyHeadName :: Lens' TypeFamilyHead Name

   lens	Language.Haskell.TH.Lens

   No documentation available.

5. typeFamilyHeadResultSig :: Lens' TypeFamilyHead FamilyResultSig

   lens	Language.Haskell.TH.Lens

   No documentation available.

6. typeFamilyHeadTyVarBndrs :: Lens' TypeFamilyHead [TyVarBndrVis]

   lens	Language.Haskell.TH.Lens

   No documentation available.

7. lookAhead :: forall s (m :: Type -> Type) t u a . Stream s m t => ParsecT s u m a -> ParsecT s u m a

   parsec	Text.Parsec

   lookAhead p parses p without consuming any input. If p fails and consumes some input, so does lookAhead. Combine with try if this is undesirable.

8. lookAhead :: forall s (m :: Type -> Type) t u a . Stream s m t => ParsecT s u m a -> ParsecT s u m a

   parsec	Text.Parsec.Combinator

   lookAhead p parses p without consuming any input. If p fails and consumes some input, so does lookAhead. Combine with try if this is undesirable.

9. lookAhead :: forall s (m :: Type -> Type) t u a . Stream s m t => ParsecT s u m a -> ParsecT s u m a

   parsec	Text.Parsec.Prim

   lookAhead p parses p without consuming any input. If p fails and consumes some input, so does lookAhead. Combine with try if this is undesirable.

10. lookAhead :: forall s (m :: Type -> Type) t u a . Stream s m t => ParsecT s u m a -> ParsecT s u m a

    parsec	Text.ParserCombinators.Parsec.Combinator

    lookAhead p parses p without consuming any input. If p fails and consumes some input, so does lookAhead. Combine with try if this is undesirable.

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