[plt-scheme] iterate over characters in string

ptg at ccs.neu.edu writes:

> Chris, here's a fairly non-verbose version:
> 
>   ; : str -> nat
>   (define (checksum line)
>     (modulo (apply + (map char->integer (string->list line))) 256))

Very nice! (in terms of verbosity)

> For practice, see if you can write one using the foldl function instead
> of map and apply.

I'll look into that.

> If the intermediate list bothers you, either look up
> string-ref, or implement a deforestation compiler pass for mzscheme :-)

The "deforestation" compiler pass is a term I've never heard, but I
assume you mean to write an mzscheme extension that does this?  That
was what I was thinking would be necessary unless it had already been
done, in which case I'd rather not re-invent the wheel.

> The best way to good performance is to implement a handful of versions
> and benchmark them.  DrScheme's profiler will help.

I've just made the move to v200 from 1.03.  I'm looking forward to
using the profiler.

-- 
Chris