[project @ 2001-06-28 14:15:04 by simonmar]

First cut of the Haskell Core Libraries
=======================================

NOTE: it's not meant to be a working snapshot.  The code is just here
to look at and so the NHC/Hugs guys can start playing around with it.

There is no build system.  For GHC, the libraries tree is intended to
be grafted onto an existing fptools/ tree, and the Makefile in
libraries/core is a quick hack for that setup.  This won't work at the
moment without the other changes needed in fptools/ghc, which I
haven't committed because they'll cause breakage.  However, with the
changes required these sources build a working Prelude and libraries.

The layout mostly follows the one we agreed on, with one or two minor
changes; in particular the Data/Array layout probably isn't final
(there are several choices here).

The document is in libraries/core/doc as promised.

The cbits stuff is just a copy of ghc/lib/std/cbits and has
GHC-specific stuff in it.  We should really separate the
compiler-specific C support from any compiler-independent C support
there might be.

Don't pay too much attention to the portability or stability status
indicated in the header of each source file at the moment - I haven't
gone through to make sure they're all consistent and make sense.

I'm using non-literate source outside of GHC/.  Hope that's ok with
everyone.

We need to discuss how the build system is going to work...

1 files changed, 75 insertions, 0 deletions

diff --git a/libraries/base/Data/Maybe.hs b/libraries/base/Data/Maybe.hs
new file mode 100644
index 0000000000..06c7a25398
--- /dev/null
+++ b/libraries/base/Data/Maybe.hs
@@ -0,0 +1,75 @@
+{-# OPTIONS -fno-implicit-prelude #-}
+-----------------------------------------------------------------------------
+-- 
+-- Module      :  Data.Maybe
+-- Copyright   :  (c) The University of Glasgow 2001
+-- License     :  BSD-style (see the file libraries/core/LICENSE)
+-- 
+-- Maintainer  :  libraries@haskell.org
+-- Stability   :  experimental
+-- Portability :  non-portable
+--
+-- $Id: Maybe.hs,v 1.1 2001/06/28 14:15:02 simonmar Exp $
+--
+-- The Maybe type, and associated operations.
+--
+-----------------------------------------------------------------------------
+
+module Data.Maybe
+   (
+     Maybe(Nothing,Just)-- instance of: Eq, Ord, Show, Read,
+			--		Functor, Monad, MonadPlus
+
+   , maybe		-- :: b -> (a -> b) -> Maybe a -> b
+
+   , isJust		-- :: Maybe a -> Bool
+   , isNothing		-- :: Maybe a -> Bool
+   , fromJust		-- :: Maybe a -> a
+   , fromMaybe		-- :: a -> Maybe a -> a
+   , listToMaybe        -- :: [a] -> Maybe a
+   , maybeToList	-- :: Maybe a -> [a]
+   , catMaybes		-- :: [Maybe a] -> [a]
+   , mapMaybe		-- :: (a -> Maybe b) -> [a] -> [b]
+   ) where
+
+#ifdef __GLASGOW_HASKELL__
+import GHC.Err	( error )
+import GHC.List
+import GHC.Maybe
+import GHC.Base
+#endif
+
+isJust         :: Maybe a -> Bool
+isJust Nothing = False
+isJust _       = True
+
+isNothing         :: Maybe a -> Bool
+isNothing Nothing = True
+isNothing _       = False
+
+fromJust          :: Maybe a -> a
+fromJust Nothing  = error "Maybe.fromJust: Nothing" -- yuck
+fromJust (Just x) = x
+
+fromMaybe     :: a -> Maybe a -> a
+fromMaybe d x = case x of {Nothing -> d;Just v  -> v}
+
+maybeToList            :: Maybe a -> [a]
+maybeToList  Nothing   = []
+maybeToList  (Just x)  = [x]
+
+listToMaybe           :: [a] -> Maybe a
+listToMaybe []        =  Nothing
+listToMaybe (a:_)     =  Just a
+ 
+catMaybes              :: [Maybe a] -> [a]
+catMaybes ls = [x | Just x <- ls]
+
+mapMaybe          :: (a -> Maybe b) -> [a] -> [b]
+mapMaybe _ []     = []
+mapMaybe f (x:xs) =
+ let rs = mapMaybe f xs in
+ case f x of
+  Nothing -> rs
+  Just r  -> r:rs
+