Optional Static Typing

[Jacek Generowicz]

aleaxit at yahoo.com (Alex Martelli) writes:

> I've always liked the (theoretical) idea that assertions (including of
> course contracts) could be used as axioms used to optimize generated
> code, rather than (necessarily) as a runtime burden.  E.g. (and I don't
> know of any implementation of this concept, mind you), inferring (e.g.
> from such assertions) that x>=0, and that y<0, the compiler could simply
> cut away a branch of dead code guarded by "if x<y:" (maybe with a
> warning, in this case;-)...

A few months ago, a troll challenged the denizens of comp.lang.lisp to
write a Lisp implementation of some some code which he posted in C++,
which would be competitive in terms of speed with his C++
version. The c.l.lers duly obliged, and, IIRC, it so happened that the
improvement that made the Lisp version overtake the C++ one was the
declaration of some variable to be of type "floating point number in
the range 0 to two Pi".

Of course, in CL type declarations are not contracts, but promises to
the compiler ... but it's still an examlpe of a situation where more
specific type information allowed the compiler to produce more
efficient code, in practice.