[racket-dev] racket/match is broken

From: Robby Findler (robby at eecs.northwestern.edu)
Date: Sat Oct 8 12:29:52 EDT 2011

On Sat, Oct 8, 2011 at 11:17 AM, Matthias Felleisen
<matthias at ccs.neu.edu> wrote:
> On Oct 5, 2011, at 10:48 PM, Jay McCarthy wrote:
>> Okay. I think it is strange, but feel free to do that and revert my
>> change. Apologies for the confusion.

> I think you shouldn't apologize here. I am unhappy that match
> doesn't guarantee order of matching in a list.
> Sam should change the implementation not the documentation.

I'm hoping to eventually use match for redex in order to get some
performance improvement and I fear that disabling these optimizations
would be bad news for me there. So I hope that's not what happens

I don't mind if the ordering of calling the predicates is fixed when
match cannot prove that the predicates are all safe to be reordered
(presumably by match keeping a list of known-to-be-safe predicates
somewhere and perhaps looking at the compile-time info to find struct

(That would seem to be a straight-forward change, unless I'm missing something.)

> The entire reason
> I use lists is that I want left-to-right traversals. If I don't
> I use 'no order' patterns.

I don't think the above makes sense. Presumably you use lists when you
want to *match* from left to right and no order when you don't care
about the order of *matching the elements in the list*.

But that's not really relevant for this discussion.


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