>I don't understand why the compiler don't do himself those transformations.
>Why is it so hard to take a non-tail-recursive-function and make it a 
>tail-recursive-one ?

Because in the general case that would change the intent of the program.

Imagine if you have a sequence of two expressions with side-effects, or 
with significant order (e.g. consing a value to a function that returns a 
list).  Changing the order automatically would have the wrong effect.

Boy, some people want computers to do ALL our thinking. ;-)

Marc