Initial import of dlist package

darcs-hash:20061211032153-9c5c1-ffa6da3f510681db5293d3cac0a0a4b8a4a3dcbf

Data/DList.hs

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+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.DList
+-- Copyright   :  (c) Don Stewart 2006
+-- License     :  BSD-style (see the file LICENSE)
+--
+-- Maintainer  :  [email protected]
+-- Stability   :  experimental
+-- Portability :  portable (Haskell 98)
+--
+-- Difference lists: a data structure for O(1) append on lists.
+--
+-----------------------------------------------------------------------------
+
+module Data.DList (
+
+  DList,        -- abstract
+
+  -- * Construction
+  fromList,     -- :: [a] -> DList a
+  toList,       -- :: DList a -> [a]
+
+  -- * Basic functions
+  empty,        -- :: DList a
+  singleton,    -- :: a -> DList a
+  snoc,         -- :: DList a -> a -> DList a
+  append,       -- :: DList a -> DList a -> DList a
+
+
+  ) where
+
+-- | A difference list is a function that given a list, returns the
+-- original contents of the difference list prepended at the given list
+--
+-- This structure supports /O(1)/ append/snoc operations on lists
+--
+type DList a = [a] -> [a]
+
+-- | Converting a normal list to a dlist
+fromList    :: [a] -> DList a
+fromList    = (++)
+
+-- | Converting a dlist back to a normal list
+toList      :: DList a -> [a]
+toList      = ($[])
+
+-- | Create a difference list containing no elements
+empty       :: DList a
+empty       = id
+
+-- | Create difference list with given single element
+singleton   :: a -> DList a
+singleton   = (:)
+
+-- | /O(1)/, Append a single element at a difference list
+snoc        :: DList a -> a -> DList a
+snoc        = (. (:)) . (.)
+
+-- | Appending difference lists
+append      :: DList a -> DList a -> DList a
+append      = (.)

Setup.lhs

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+#!/usr/bin/env runhaskell
+> import Distribution.Simple
+> main = defaultMain

dlist.cabal

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+Name:                dlist
+Version:             0.1
+Description:         Differences lists: lists supporting efficient append
+License:             BSD3
+License-file:        LICENSE
+Author:              Don Stewart 
+Maintainer:          <[email protected]>
+Build-Depends:       base
+ghc-options:         -O
+Exposed-modules:     Data.DList