comments for Applicative and Traversable

[ghc-base.git] / Control / Applicative.hs

diff --git a/Control/Applicative.hs b/Control/Applicative.hs
index fa78371..2149b7a 100644 (file)
--- a/Control/Applicative.hs
+++ b/Control/Applicative.hs
@@ -59,6 +59,12 @@ infixl 4 <*>, <*, *>, <**>
 -- [/interchange/]
 --     @u '<*>' 'pure' y = 'pure' ('$' y) '<*>' u@
 --
+-- The 'Functor' instance should satisfy
+--
+-- @
+--     'fmap' f x = 'pure' f '<*>' x
+-- @
+--
 -- If @f@ is also a 'Monad', define @'pure' = 'return'@ and @('<*>') = 'ap'@.
 
 class Functor f => Applicative f where