Abstrakte Datentypen

= verberge (verbiete Benutzung von) Konstruktion der Typelemente

Lösung in Haskell: Konventionell, nämlich:

• verpacke Typdefinition + einschlägige Operationsdefinitionen in Modul
• exportiere nur das, was der Anwender benutzen soll, also zB Typ- und Operationsbezeichner in "`Exportliste"'.

Seite

Haskells Modulkonzept wird von verschiedenen Hugs-Versionen nicht (vollständig) unterstützt; umgekehrt bieten Gofer/Hugs Systemeigene (nicht-Haskell) Syntax für abstrakte Datentypen.

 


-----------------------------ADT module

module Searchtree(STree, listToSTree, sTreeToList) where






data Ord a => STree a = Node a (STree a) (STree a) | Nil






insertSTree :: Ord a => a -> STree a -> STree a

insertSTree x Nil = Node x Nil Nil

insertSTree x (Node y left right)

   | x<=y       = Node y (insertSTree x left) right

   | otherwise  = Node y left (insertSTree x right)






listToSTree :: Ord a => [a] -> STree a

listToSTree = foldr insertSTree Nil






sTreeToList :: Ord a => STree a -> [a]

sTreeToList Nil = []

sTreeToList (Node x left right)

   = (sTreeToList left) ++ [x] ++ (sTreeToList right)






-------------------client module (separate file)






module Main where

import Searchtree           - improt complete export of Searchtree






-----------------------------use e.g.:






{-

Prelude> :l Main.hs

Reading file "Main.hs":

Reading file "Searchtree.hs":

Reading file "Main.hs":






Hugs session for:

/usr/local/share/hugs/lib/Prelude.hs

Searchtree.hs

Main.hs

Main> (sTreeToList.listToSTree) [1,-1,0,2,-2]

[-2, -1, 0, 1, 2]

Main> sTreeToList (insertSTree 2 Nil)  -insertSTree is hidden!

ERROR: Undefined variable "insertSTree"

Main> sTreeToList Nil                  - constructors are hidden!

ERROR: Undefined constructor function "Nil"

-}