Aufgabe 3.1

type N = Char

type V = Integer

data Definitions = NoDefinitions
						| Definitions N V Definitions
						deriving Show

find :: N -> Definitions -> V
find name NoDefinitions = error "Variable not found in List!"
find name (Definitions dname dvar def) = if name==dname
															then dvar
															else find name def

contains :: N -> Definitions -> Bool
contains name NoDefinitions = False
contains name (Definitions dname dvar def) = if name==dname
															then True
															else contains name def

addDefinition :: N -> V -> Definitions -> Definitions
addDefinition name var toReplacIn = replaceDef NoDefinitions name var toReplacIn

addToList  :: Definitions -> Definitions -> Definitions
addToList NoDefinitions def = def
addToList (Definitions n m NoDefinitions)  toAdd = Definitions n m toAdd
addToList (Definitions n m def) toAdd = Definitions n m (addToList def toAdd)

replaceDef :: Definitions -> N -> V -> Definitions -> Definitions
replaceDef preDef name var (Definitions postName postVar NoDefinitions) = if name==postName
																												then addToList preDef (Definitions name var NoDefinitions)
																												else addToList preDef (Definitions postName postVar (Definitions name var NoDefinitions))
replaceDef preDef name var (Definitions postName postVar postDef) = if name==postName
																										then addToList (addToList preDef (Definitions name var NoDefinitions)) postDef
																										else replaceDef (addToList preDef (Definitions postName postVar NoDefinitions)) name var postDef