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Gepostet:
02.07.2005 11:23

Haskell problems

Hi
I have three problems about haskell,

1.Compare the polymorphic, higher-order and laziness features of Haskell with Java
or C/C++ , which is the better? Are there some good examples.

2. On the features of Type class of Haskell and its application (Please give me some
examples)
3. which kind of the examples can reflect the features of Haskell.

thanks

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Jacke

Gepostet:
03.07.2005 16:15

1)
example in C++

template<class T>
void swap(T& x, T& y) {
T temp = x;
x = y;
y = temp;
}

appliance:

int i,j; swap<int> (i,j); //a swap for int
char i,j; swap<char>(i,j); //a swap for char

without explicit datatype

java

example: java.util.Stack class

class Stack<E> extends Vector<E> {
public E push(E item) {..}
public synchronized E pop() {..}
public synchronized E peek() {..}
public boolean empty() {..}
public synchronized int search(Object o) {..}
}

appliance:

Stack<String> foo = new Stack<String>();

method genericity:
static <Elem> void swap(Elem[] array, int x, int y) {
Elem temp = array[x];
array[x] = array[y];
array[y] = temp;
}

haskell

swap (x,y) =(y,x)

shorter ...
2)
in haskell you can create own types
example:
type Person=String
type Book= String

type Database=[(Person, Book)] --list of tupels from persons and Books

makeloan::Database->Person->Book->Database
makeloan examplebase (aperson,abook)=examplebase++[(aperson,abook)]

-------------------------------------------------------------------------
3)
also polymorphism
fst (x,y)=x

snd(x,y)=y

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