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1. (<$) :: Functor f => a -> f b -> f a

   base	Data.Functor

   Replace all locations in the input with the same value. The default definition is fmap . const, but this may be overridden with a more efficient version.

   Examples

   Perform a computation with Maybe and replace the result with a constant value if it is Just:

   >>> 'a' <$ Just 2
   Just 'a'
   
   >>> 'a' <$ Nothing
   Nothing
   

2. (<$>) :: Functor f => (a -> b) -> f a -> f b

   base	Data.Functor

   An infix synonym for fmap. The name of this operator is an allusion to $. Note the similarities between their types:

   ($)  ::              (a -> b) ->   a ->   b
   (<$>) :: Functor f => (a -> b) -> f a -> f b
   

   Whereas $ is function application, <$> is function application lifted over a Functor.

   Examples

   Convert from a Maybe Int to a Maybe String using show:

   >>> show <$> Nothing
   Nothing
   

   >>> show <$> Just 3
   Just "3"
   

   Convert from an Either Int Int to an Either Int String using show:

   >>> show <$> Left 17
   Left 17
   

   >>> show <$> Right 17
   Right "17"
   

   Double each element of a list:

   >>> (*2) <$> [1,2,3]
   [2,4,6]
   

   Apply even to the second element of a pair:

   >>> even <$> (2,2)
   (2,True)
   

3. (>$) :: Contravariant f => b -> f b -> f a

   base	Data.Functor.Contravariant

   Replace all locations in the output with the same value. The default definition is contramap . const, but this may be overridden with a more efficient version.

4. (>$$<) :: Contravariant f => f b -> (a -> b) -> f a

   base	Data.Functor.Contravariant

   This is an infix version of contramap with the arguments flipped.

5. (>$<) :: Contravariant f => (a -> b) -> f b -> f a

   base	Data.Functor.Contravariant

   This is an infix alias for contramap.

6. (<$) :: Functor f => a -> f b -> f a

   base	GHC.Base

   Replace all locations in the input with the same value. The default definition is fmap . const, but this may be overridden with a more efficient version.

   Examples

   Perform a computation with Maybe and replace the result with a constant value if it is Just:

   >>> 'a' <$ Just 2
   Just 'a'
   
   >>> 'a' <$ Nothing
   Nothing
   

7. (:$$:) :: ErrorMessage -> ErrorMessage -> ErrorMessage

   base	GHC.TypeError

   Stack two pieces of error message on top of each other.

8. (:$$:) :: ErrorMessage -> ErrorMessage -> ErrorMessage

   base	GHC.TypeLits

   Stack two pieces of error message on top of each other.

9. (>$<) :: Contravariant f => (b -> a) -> f a -> f b

   bytestring	Data.ByteString.Builder.Prim

   A fmap-like operator for builder primitives, both bounded and fixed size. Builder primitives are contravariant so it's like the normal fmap, but backwards (look at the type). (If it helps to remember, the operator symbol is like ($) but backwards.) We can use it for example to prepend and/or append fixed values to an primitive.

   import Data.ByteString.Builder.Prim as P
   showEncoding ((\x -> ('\'', (x, '\''))) >$< fixed3) 'x' = "'x'"
   where
   fixed3 = P.char7 >*< P.char7 >*< P.char7
   

   Note that the rather verbose syntax for composition stems from the requirement to be able to compute the size / size bound at compile time.

10. (>$<) :: Contravariant f => (b -> a) -> f a -> f b

    bytestring	Data.ByteString.Builder.Prim.Internal

    A fmap-like operator for builder primitives, both bounded and fixed size. Builder primitives are contravariant so it's like the normal fmap, but backwards (look at the type). (If it helps to remember, the operator symbol is like ($) but backwards.) We can use it for example to prepend and/or append fixed values to an primitive.

    import Data.ByteString.Builder.Prim as P
    showEncoding ((\x -> ('\'', (x, '\''))) >$< fixed3) 'x' = "'x'"
    where
    fixed3 = P.char7 >*< P.char7 >*< P.char7
    

    Note that the rather verbose syntax for composition stems from the requirement to be able to compute the size / size bound at compile time.

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