Comments for Sententia cdsmithus

Comment on View Patterns as Pattern Matching for Records by Anonymous

Anonymous — Sat, 07 Nov 2009 18:46:32 +0000

Oh, I like that one… without the special function, one can still do (slightly more messy)

foo (replicate 3 -> [ (^.field1) -> Just k, (^.field2) -> 4, (^.field3) -> (x:_) ]) = 4*k – x

Comment on View Patterns as Pattern Matching for Records by Dan Licata

Dan Licata — Sat, 07 Nov 2009 15:37:26 +0000

Also I meant to mention that this use of view patterns is very cool! Nice idea! :)

Comment on View Patterns as Pattern Matching for Records by Dan Licata

Dan Licata — Sat, 07 Nov 2009 15:31:21 +0000

You can already kind of match on a value multiple times with view patterns: just define a function that pairs the value with itself the appropriate number of times.

Instead of

foo :: MyRecord -> Int
foo ((^.field1) -> Just k ; (^.field2) -> 4 ; (^.field3) -> (x:_)) = 4*k – x

write

three x = (x , x , x)
foo (three -> ((^.field1) -> Just k , (^.field2) -> 4 , (^.field3) -> (x:_))) = 4*k – x

Comment on The "X Improves My Design Anyway" Myth by CurtainDog

CurtainDog — Sat, 07 Nov 2009 07:55:06 +0000

Well, it at a minimum it does improve your design to the extent that others are able to quickly grok what you’re trying to do. For example I may see something like a singleton and have to suppress the urge to retch but at least I know whats going on.

When it comes to architectural decisions we can argue pragmatism vs principle until the cows come home, but I’ve seen some nightmares in the security and performance realms when developers have gone for pragmatism.

Comment on Functions and Partial Orders by Roy33

Roy33 — Thu, 22 Oct 2009 07:28:58 +0000

DNS client and server implementations will typically discard non-matching responses and continue to wait for a matching response. ,

Comment on View Patterns as Pattern Matching for Records by Ravi

Ravi — Sun, 18 Oct 2009 04:30:57 +0000

I think that would be very interesting. I’d love to see you try to implement this extension (and, of course, as someone on the Haskell’ committee, to see you turn this into a proposal for a future revision of Haskell if it works out well).

Comment on What To Know Before Debating About Type Systems by Anonymous

Anonymous — Sat, 17 Oct 2009 17:48:53 +0000

http://www.pphsg.org/cdsmith/types.html

Comment on View Patterns as Pattern Matching for Records by Edward Kmett

Edward Kmett — Fri, 09 Oct 2009 18:07:10 +0000

@Ben:

Note that @ bindings currently only allow for a simple variable name to be bound on the left hand side of the @, so allowing @ bindings in this setting would require a fairly invasive retooling of how @ works inside patterns.

Comment on View Patterns as Pattern Matching for Records by Ben Moseley

Ben Moseley — Sun, 04 Oct 2009 17:23:48 +0000

That’s an interesting idea. Derek’s is a nice interim solution, but I agree with Chris that simultaneous pattern-matching seems like a nice thing. Maybe @ could be reused rather than ; …

Comment on View Patterns as Pattern Matching for Records by Derek Elkins

Derek Elkins — Sun, 04 Oct 2009 16:45:28 +0000

foo :: MyRecord -> Int
foo r | Just k <- r ^. field1, 4 <- r ^. field2, x:_ <- r ^. field3 = 4*k – x