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Re: Common Lisp solved this problem 20 years ago

This page is part of the web mail archives of SRFI 77 from before July 7th, 2015. The new archives for SRFI 77 contain all messages, not just those from before July 7th, 2015.

I don't like the Kawa "coercion" semantic for type declarations; I don't think it is wrong per se, but I much prefer Common Lisps "assertion" semantics. That is, in Common Lisp, if I declare that a variable has a certain type, the compiler can do just about anything, provided the program works correctly when the variable has that type. Common behaviours are:

(a) Doing nothing.

(b) Complaining if the variable does not have that type.

(c) Assuming that the variable has that type and and acting in a way that will be dangerous if it does not.

These are often offered as compilation options. They seem to offer a wider range of useful behaviour and a wider range of trade-offs between safety and optimization.

The "assertion" semantics also more naturally extend to limited ranges (e.g., asserting that an integer is non-zero) or using unions of types.


Dr Alan Watson
Centro de Radioastronomía y Astrofísica
Universidad Astronómico Nacional de México