Trying Haskell

Haskell's type system can also express interesting things most languages' type systems can't.<p>For example:<p><a href="https://github.com/yairchu/red-black-tree/blob/master/AvlTree.hs" rel="nofollow">https://github.com/yairchu/red-black-tree/blob/master/AvlTre...</a> -- in lines 13..21, an AVLTree type is defined -- with its invariants encoded in the type system. If there's a mistake in these 9 lines, you may get a wrong program. But the nice thing is that if you get just these 9 lines right -- then the hundreds of lines below it that implement an AVL tree <i></i>cannot get the AVL invariants wrong<i></i>.<p>The same is also true for Red Black Trees: <a href="https://github.com/yairchu/red-black-tree/blob/master/RedBlackTree.hs" rel="nofollow">https://github.com/yairchu/red-black-tree/blob/master/RedBla...</a><p>Lines 26..36 inclusive encode the RBTree type such that the invariants are enforced by the type-checker.<p>In case this is unclear: the type-checker enforcing the correctness of the invariants is at <i>compile-time</i>. A running program is a correct program, at least from the invariants' perspective.

"Oh look, Haskell is great! Why? Static typing and concise code and no side effects!"<p>I don't disagree on any particular point, but this is hardly news (on HN, at least), and is rather lacking in substance.

Obligatory comment pointing out that the fabled "quicksort" example in Haskell is not actually quicksort proper since it's not in-place.

C++ quicksort :|<p><pre><code> #include &#60;algorithm&#62; #include &#60;iterator&#62; #include &#60;functional&#62; using namespace std; template &#60;typename T&#62; void sort(T begin, T end) { if (begin != end) { T middle = partition (begin, end, bind2nd(less&#60;iterator_traits&#60;T&#62;::value_type&#62;(), *begin)); sort (begin, middle); sort (max(begin + 1, middle), end); } } </code></pre> from wikipedia