[racket-dev] Falling through cond clauses

From: Jay McCarthy (jay.mccarthy at gmail.com)
Date: Tue Oct 2 10:11:14 EDT 2012

In addition to this, I want internal definitions in conds:

 [test1 body1]
 (define var ...)
 [(test2 var) body2]
 [(test3 var) body3])

I have a macro that does these things:


It's pretty cute


On Tue, Oct 2, 2012 at 7:58 AM, Carl Eastlund <cce at ccs.neu.edu> wrote:
> Oh, no, as far as a "does it work out of the box" experiment goes, it fails.
> Racket doesn't even compile.  I meant more along the lines of our
> immutable-cons experiment, where we fix a bunch of code and see how
> problematic the compatibility issue becomes over time.
> Carl Eastlund
> On Tue, Oct 2, 2012 at 9:56 AM, J. Ian Johnson <ianj at ccs.neu.edu> wrote:
>> This experiment should be easy to run, no? Change the default cond and run
>> DrDr?
>> -Ian
>> ----- Original Message -----
>> From: "Carl Eastlund" <cce at ccs.neu.edu>
>> To: "Racket Developers" <dev at racket-lang.org>
>> Sent: Tuesday, October 2, 2012 9:52:38 AM GMT -05:00 US/Canada Eastern
>> Subject: [racket-dev] Falling through cond clauses
>> I often wish cond would raise an exception if all the tests failed and
>> there were no else clause. I have taken to writing a macro to enforce this;
>> I usually call it cond!. The void default for cond seems like an
>> un-Racketish holdover from primarily-imperative programming. With some of
>> the other changes we've made in Racket, are we willing to consider changing
>> the fall-through behavior of cond? It seems like an experiment worth running
>> to me.
>> If not, I would at least like to add an erroring version of cond somewhere
>> in the language. It's a shame to have to keep writing such a primitive
>> feature. Right now in my dracula github repo I have cond! implemented in
>> racket/cond and re-exported from racket, but I'm not thrilled about either
>> the location or the name. I kept it out of racket/base so I could depend on
>> the syntax collection for good source location reporting in the error
>> message.
>> Carl Eastlund
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Jay McCarthy <jay at cs.byu.edu>
Assistant Professor / Brigham Young University

"The glory of God is Intelligence" - D&C 93

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