>>>    What would the harm be if eg. list nodes were structs instead?
>
>> Since "null" is a union in Haskell to (i.e., it either has data in it or it
>> has no data in it), this wouldn't really save you anything.
>
>    It saves checking the node type for each single operation you do to any
> node in the list. It the node is a struct, its contents are fixed and thus
> you don't have to check anything.

On the other hand, in a language where unions appear all over the place, 
the implementors go to great lengths to make it really efficient.

Besides, normally just about any code that does stuff to a linked list 
ends up doing something like

   while (list != null)
     do stuff;
     list = next node;

So there's a check in there anyway. All we're doing by using a union is 
making it a different check.

-- 
http://blog.orphi.me.uk/
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