[project @ 2005-03-14 15:22:51 by simonmar]

[ghc-base.git] / GHC / Base.lhs

diff --git a/GHC/Base.lhs b/GHC/Base.lhs
index 7d310b7..5b6a676 100644 (file)
--- a/GHC/Base.lhs
+++ b/GHC/Base.lhs
@@ -81,6 +81,7 @@ Other Prelude modules are much easier with fewer complex dependencies.
 
 #include "MachDeps.h"
 
+-- #hide
 module GHC.Base
        (
        module GHC.Base,
@@ -208,14 +209,22 @@ Instances of 'Functor' should satisfy the following laws:
 > fmap id  ==  id
 > fmap (f . g)  ==  fmap f . fmap g
 
-The instances of 'Functor' for lists, 'Maybe' and 'IO' defined in the "Prelude"
-satisfy these laws.
+The instances of 'Functor' for lists, 'Data.Maybe.Maybe' and 'System.IO.IO'
+defined in the "Prelude" satisfy these laws.
 -}
 
 class  Functor f  where
     fmap        :: (a -> b) -> f a -> f b
 
-{- | The 'Monad' class defines the basic operations over a /monad/.
+{- | The 'Monad' class defines the basic operations over a /monad/,
+a concept from a branch of mathematics known as /category theory/.
+From the perspective of a Haskell programmer, however, it is best to
+think of a monad as an /abstract datatype/ of actions.
+Haskell's @do@ expressions provide a convenient syntax for writing
+monadic expressions.
+
+Minimal complete definition: '>>=' and 'return'.
+
 Instances of 'Monad' should satisfy the following laws:
 
 > return a >>= k  ==  k a
@@ -226,16 +235,26 @@ Instances of both 'Monad' and 'Functor' should additionally satisfy the law:
 
 > fmap f xs  ==  xs >>= return . f
 
-The instances of 'Monad' for lists, 'Maybe' and 'IO' defined in the "Prelude"
-satisfy these laws.
+The instances of 'Monad' for lists, 'Data.Maybe.Maybe' and 'System.IO.IO'
+defined in the "Prelude" satisfy these laws.
 -}
 
 class  Monad m  where
+    -- | Sequentially compose two actions, passing any value produced
+    -- by the first as an argument to the second.
     (>>=)       :: forall a b. m a -> (a -> m b) -> m b
+    -- | Sequentially compose two actions, discarding any value produced
+    -- by the first, like sequencing operators (such as the semicolon)
+    -- in imperative languages.
     (>>)        :: forall a b. m a -> m b -> m b
        -- Explicit for-alls so that we know what order to
        -- give type arguments when desugaring
+
+    -- | Inject a value into the monadic type.
     return      :: a -> m a
+    -- | Fail with a message.  This operation is not part of the
+    -- mathematical definition of a monad, but is invoked on pattern-match
+    -- failure in a @do@ expression.
     fail       :: String -> m a
 
     m >> k      = m >>= \_ -> k
@@ -671,9 +690,20 @@ id x                       =  x
 lazy :: a -> a
 lazy x = x
 
--- | Assertion function.  This simply ignores its boolean argument.
+-- Assertion function.  This simply ignores its boolean argument.
 -- The compiler may rewrite it to @('assertError' line)@.
 
+-- | If the first argument evaluates to 'True', then the result is the
+-- second argument.  Otherwise an 'AssertionFailed' exception is raised,
+-- containing a 'String' with the source file and line number of the
+-- call to 'assert'.
+--
+-- Assertions can normally be turned on or off with a compiler flag
+-- (for GHC, assertions are normally on unless the @-fignore-asserts@
+-- option is given).  When assertions are turned off, the first
+-- argument to 'assert' is ignored, and the second argument is
+-- returned as the result.
+
 --     SLPJ: in 5.04 etc 'assert' is in GHC.Prim,
 --     but from Template Haskell onwards it's simply
 --     defined here in Base.lhs