[racket] Vast performance differences with minute syntactic differences

I wrote two set-adds? Ugh, I didn't mean to. That code wouldn't even work due to arity mismatch. 
(set-add res (let ([v v]) v)) is more likely.
-Ian
----- Original Message -----
From: Sam Tobin-Hochstadt <samth at ccs.neu.edu>
To: J. Ian Johnson <ianj at ccs.neu.edu>
Cc: users <users at racket-lang.org>
Sent: Thu, 4 Oct 2012 19:46:36 -0400 (EDT)
Subject: Re: [racket] Vast performance differences with minute syntactic differences

On Thu, Oct 4, 2012 at 7:01 PM, J. Ian Johnson <ianj at ccs.neu.edu> wrote:
>
> By almost exactly I mean
> (let () (set-add res v))
>
> versus
>
> (let ([res res])
>  (set-add (let ([v v])
>              (set-add res (let () v)))))

These seem importantly different, in that:

(set-add v (set-add res v))

and

(set-add res v)

are totally different values, and the former only works if both `v`
and `res` are sets.

If you want to determine the behavior of the compiler, which is what
matters for differences like extra `let` bindings, 'raco decompile' is
the best tool.
-- 
sam th
samth at ccs.neu.edu