It's because there's an application of a strict function,
the dictionary selector 'a'. In general, if f is strict
then f (g x)
is turned into
case g x of y { DEFAULT -> f y }
But it is rather inscrutable. It didn't arise from a strictness
annotation put in by the user.
The right thing to do is to fix the bytecode generator.
Simon
| -----Original Message-----
| From: Julian Seward (Intl Vendor)
| Sent: 08 February 2002 13:55
| To: 'Dean Herington'; [EMAIL PROTECTED]
| Cc: Simon Peyton-Jones
| Subject: RE: inscrutable warning
|
|
|
| The warning says that the interpreter has ignored a
| polymorphic case, since it's hard to implement. Your program
| should still behave the same, although possibly less strictly
| than you intended.
|
| What really mystifies us is why there is such a thing in the
| program in the first place. Using -ddump-sat we can see that
| there is indeed a
| case ... of { DEFAULT -> ... }
| but how it came to be, I do not know.
|
| We may investigate further.
|
| J
|
| | Can someone explain the following warning?
| |
| | -------------------------------
| | module Warning where
| |
| | type A = IO ()
| |
| | class CA t
| | where a :: t -> A
| | instance CA ()
| | where a = return
| | instance (CA t) => CA (IO t)
| | where a = (>>= a)
| |
| | data B = B A
| |
| | class CB t
| | where b :: t -> B
| | instance (CA t) => CB (IO t)
| | where b = B . a
| | -------------------------------
| |
| | % ghci Warning.hs
| | ___ ___ _
| | / _ \ /\ /\/ __(_)
| | / /_\// /_/ / / | | GHC Interactive, version 5.02.2,
| | for Haskell
| | 98.
| | / /_\\/ __ / /___| | http://www.haskell.org/ghc/
| | \____/\/ /_/\____/|_| Type :? for help.
| |
| | Loading package std ... linking ... done.
| | Compiling Warning ( Warning.hs, interpreted )
| | WARNING: ignoring polymorphic case in interpreted mode.
| | Possibly due to strict polymorphic/functional constructor args.
| | Your program may leak space unexpectedly.
| |
| | Ok, modules loaded: Warning.
| | Warning>
| |
| | _______________________________________________
| | Glasgow-haskell-users mailing list
| | [EMAIL PROTECTED]
| | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
| |
|
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