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| author | Ross Paterson <ross@soi.city.ac.uk> | 2009-01-16 15:16:24 +0000 |
|---|---|---|
| committer | Ross Paterson <ross@soi.city.ac.uk> | 2009-01-16 15:16:24 +0000 |
| commit | ed1a8c2e37d94fa6677f10cb7dcc2c348ce9c0bb (patch) | |
| tree | 504bf904b47cce729e9d25e88c1440991b75ee4d /libraries/base/Data/Monoid.hs | |
| parent | d49ea2e7f573aaae379e434c52df429651bd3ff4 (diff) | |
| download | haskell-ed1a8c2e37d94fa6677f10cb7dcc2c348ce9c0bb.tar.gz | |
add Monoid laws
Diffstat (limited to 'libraries/base/Data/Monoid.hs')
| -rw-r--r-- | libraries/base/Data/Monoid.hs | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/libraries/base/Data/Monoid.hs b/libraries/base/Data/Monoid.hs index a0e3b20eff..65e3bb76d7 100644 --- a/libraries/base/Data/Monoid.hs +++ b/libraries/base/Data/Monoid.hs @@ -40,7 +40,17 @@ import Test.QuickCheck -- --------------------------------------------------------------------------- -- | The class of monoids (types with an associative binary operation that --- has an identity). The method names refer to the monoid of lists, +-- has an identity). Instances should satisfy the following laws: +-- +-- * @mempty `mappend` x = x@ +-- +-- * @x `mappend` mempty = x@ +-- +-- * @x `mappend` (y `mappend` z) = (x `mappend` y) `mappend` z@ +-- +-- * @mconcat = 'foldr' mappend mempty@ +-- +-- The method names refer to the monoid of lists under concatenation, -- but there are many other instances. -- -- Minimal complete definition: 'mempty' and 'mappend'. |