[racket-dev] Optional equality predicate for assoc and member

30 minutes ago, Matthias Felleisen wrote:
> 
> This is way overdue. Thanks. 

+1.


40 minutes ago, Vincent St-Amour wrote:
> With this patch, assoc and member are implemented in Racket. They
> are currently implemented in C. I haven't measured the performance
> impact of the change, but I can do it if someone believes it's
> necessary.

One way to make it fast is to have it bound to a macro so (member f l
eq?) expands to a `memq', and when used as a function have it dispatch
to `memq' if given `eq?'.  Then, if the racket version is fast enough,
then you can do something similar to what `sort' does -- implement it
with a macro that generates the body, use the macro a few times to get
compiled versions of the function with `eq?' etc hard wired (and
therefore inlined), and then do the same kind of dispatch over the
results.  One benefit of that is that you can use additional common
cases like `='.  The implementation of `sort' does this with one more
trick that Matthew suggested: have the macro that generates the code
be local, so that there's no need to keep it in the compiled file.

-- 
          ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
                    http://barzilay.org/                   Maze is Life!