On 27/01/06, Brian Hulley
John Meacham wrote:
On Fri, Jan 27, 2006 at 12:28:23PM +1100, Donald Bruce Stewart wrote:
john:
I have often wanted a shorthand syntax for testing if a value matches a given pattern. I want to implement such an extension for jhc but can't decide an appropriate syntax so I thought I'd ask the group. basically I want something like
/Left (Just _)/ expands to
\x -> case x of Left (Just _) -> True _ -> False
Something like pattern guards?
f x | Just _ <- x = putStrLn "something"
hmm.. how about
(| Left (Just _) |)
since | cannot be used as a section so it can be unambigously lexed as a different symbol. I think I like it. any other ideas?
John
(@ Left (Just _) @) would fit in with the use of @ in as-patterns Also, the as-pattern syntax could be stolen for expressions so that exp@pat would evaluate to True or False when this syntactic form appears in an expression instead of a pattern ie to give the following equivalence:
(@ pat @) exp === exp @ pat
Regards, Brian.
Or if we're going to allow @ as an infix operator, we could use (@ pat), reminiscent of section notation. (exp @) of course would make no sense, seeing as there's no representation for patterns as values. - Cale