[MATCH-32] Allow flattened pattern syntax at top-level to avoid nesting :when and :as Created: 12/Oct/11 Updated: 21/Oct/11 Resolved: 21/Oct/11 |
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| Status: | Resolved |
| Project: | core.match |
| Component/s: | None |
| Affects Version/s: | None |
| Fix Version/s: | None |
| Type: | Enhancement | Priority: | Minor |
| Reporter: | Steve Miner | Assignee: | Unassigned |
| Resolution: | Completed | Votes: | 0 |
| Labels: | None | ||
| Attachments: |
flat2.patch
flat3.patch
flat4.patch
flat.patch
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| Patch: | Accepted |
| Approval: | Ok |
| Description |
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On the Clojure mailing list I wrote: For guards, I wonder if the extra parens are really necessary. Couldn't the :when bind tightly to the previous pattern variable? Like Clojure FOR comprehensions. I think it would be easier to read that way. Same comment applies to :as. To cover the rare case of matching a literal :when or :as, you could quote it or use it as the first item in an OR pattern. On Oct 10, 2011, at 3:11 PM, David Nolen wrote: It would be nice to lose the extra parens - patch welcome |
| Comments |
| Comment by Steve Miner [ 12/Oct/11 10:35 AM ] |
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I attached a patch that groups the :when and :as terms appropriately given a "flattened" syntax. That is, [a :when even?] becomes [(a :when even?)] before being processed as usual. I only applied it to the top-level of the pattern row because I was concerned about recursive performance and things can get pretty complicated so maybe the magic isn't worth it. Only :when and :as at the top level get any special treatment. No mangling for :seq or ::vector, etc. No mangling of nested patterns. I also added a couple of tests for my changes. |
| Comment by Steve Miner [ 14/Oct/11 1:03 PM ] |
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I wrote an improved patch that should handle nested patterns as well. Still only groups :when and :as, not :seq since that seems sort of special. |
| Comment by Steve Miner [ 15/Oct/11 7:59 AM ] |
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Better to use seq? instead of list? |
| Comment by David Nolen [ 15/Oct/11 10:24 AM ] |
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At first glance this looks pretty neat! Will try to take a deeper look today. Thanks! |
| Comment by David Nolen [ 15/Oct/11 10:47 AM ] |
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One issue I have with this syntax enhancement - how does one match :when or :as as literals? |
| Comment by Steve Miner [ 15/Oct/11 3:13 PM ] |
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The patch tries to group the :when or :as if that makes sense. If it doesn't make sense [:when true nil], it leaves it alone so that would match the literal. In the rare case where it would be ambiguous, you would have to use a single OR pattern to get a literal match, such as [a (:when |) false]. I put something like that in one of my new tests. |
| Comment by Steve Miner [ 15/Oct/11 3:18 PM ] |
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By the way, it might be nice to allow a single element list to match that single pattern. That is, treat [(p)] the same as [p]. Right now, it's considered an error. It would also simply my patch, where I had to introduce interpose1 (as a variant of interpose) to handle an edge case with the OR pattern. |
| Comment by David Nolen [ 20/Oct/11 1:54 PM ] |
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I'm not a fan of (:when |). I'd prefer it if the patch included support for always matching literal keywords that are written as ':foo. |
| Comment by Steve Miner [ 20/Oct/11 3:04 PM ] |
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Revised patch to support ':when (and quoted keywords in general) to match the literal keyword. Updated against HEAD. |
| Comment by David Nolen [ 21/Oct/11 6:53 PM ] |
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Fixed, https://github.com/clojure/core.match/commit/d69abfaf68a86d5b9d73070e666720770779118f |
