[Haskell] Nested guards?
simonpj at microsoft.com
Wed Dec 5 10:44:14 EST 2007
Indeed this makes sense. See Section 3 of
It's really the syntactic/notational problem that has put me off every doing something like this. I just couldn't come up with a compelling syntax. (The syntax GHC uses has the great merit that it's identical to that for list comprehensions.)
| -----Original Message-----
| From: haskell-bounces at haskell.org [mailto:haskell-bounces at haskell.org] On Behalf Of Iavor Diatchki
| Sent: 04 December 2007 19:42
| To: Haskell users
| Subject: [Haskell] Nested guards?
| Lately I have been using pattern guards more than usual and I find
| that occasionally I need to nest them (i.e., I have alternatives with
| a common prefix). This seems to happen when I need to do some
| preliminary checking, followed by some decision making. Here is an
| server text
| | Just xs <- parse text
| , | "field1" `elem` xs = ... do one thing ...
| | "field2" `elem` xs = ... do something else ...
| server _ = ... invalid request ...
| As far as I can see this should be a fairly simple change to the
| pattern bindings extension. Would anyone else find this a useful
| feature, and if so what syntax should we use?
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