[racket] Rosetta code submission / string operations

From: Sean Kanaley (skanaley at gmail.com)
Date: Tue Jun 4 10:05:49 EDT 2013

Hello fellow Rosetta submitter!

The regular expressions are actually pretty useful to make a functional
version shorter than the imperative one!

First, forms with (for ...) and a bunch of (set!)'s is made functional by
(for/fold ...) where the final (values ...) functionally sets the new
Second, the regexp portion can take a converted symbol instead of a
hard-coded string to save duplicate names.

I present the following compactified implementation:

(define-values (cei cie ie ei)
  (for/fold ([cei 0] [cie 0] [ie 0] [ei 0])
    ([line (file->lines "unixdict.txt")])
    (define-syntax-rule (tally x ...)
      (values (if (regexp-match? (symbol->string 'x) line) (add1 x) x) ...))
    (tally cei cie ie ei)))

(print-rule "I before E when not preceded by C" (- ie cie) (- ei cei))
(print-rule "E before I when preceded by C" cei cie)

Since the macro would be needlessly complicated with extra conditional
logic to avoid counting "cei" as "ei", it's better to just subtract at the

I was wondering if there is some way to combine things like define-values
and for/fold...in general I find that whenever I use the functional forms
of (for...), since I will by definition care about the return values, it's
inconvenient, especially in the multiple values case, to rebind the results
to the accumulators in the for form (as seen in the above example).  In
other words, since the results of the functional versions of (for...) HAVE
to be in some way bound eventually (unless it's the entire program), it may
as well perform the binding outright and save the duplication of (let
([result (for ...)]) ...).  Perhaps anaphoric for (afor...) that binds "it"
or something like that, and for multiple values, it0, it1 ...

On Tue, Jun 4, 2013 at 9:34 AM, Tobias Hammer <tobias.hammer at dlr.de> wrote:

> Sorry for the misinformation but Eli is of course right that regexp-quote
> must be used.
> Example:
> (regexp-match? "a" "abc")
>> #t
> (regexp-match? "." "abc")
>> #t  ; WRONG! '.' matches every character
> (regexp-match? (regexp-quote "a") "abc")
>> #t
> (regexp-match? (regexp-quote ".") "abc")
>> #f
> On Tue, 04 Jun 2013 13:57:41 +0200, Daniel Prager <
> daniel.a.prager at gmail.com> wrote:
>  Thanks Tobias & Eli
>> I've updated my submission to use (regexp-match? sub-str str).
>> [Also added the stretch goal solution, but could do with some refactoring
>> to reduce the joint line-count.]
>> -- Dan
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