Using implicit parameter constraints in data decl

[Simon Peyton-Jones]

Definitely a bug.  Could you pls make a small module that elicits the
bug, and send it to me?  

Thanks

Simon

| -----Original Message-----
| From: glasgow-haskell-bugs-bounces at haskell.org
[mailto:glasgow-haskell-bugs-
| bounces at haskell.org] On Behalf Of Benjamin Franksen
| Sent: 05 November 2004 11:31
| To: glasgow-haskell-bugs at haskell.org
| Subject: Using implicit parameter constraints in data decl
| 
| This is the message from the compiler
| 
| /usr/bin/ghc -cpp  -package network -package posix -package lang
| -i../../runtime_loader -fimplicit-params     -c PluginAPI.hs -o
PluginAPI.o
| ghc-6.2.2: panic! (the `impossible' happened, GHC version 6.2.2):
|         simplCore/Simplify.lhs:1473: Non-exhaustive patterns in
function
| cat_evals
| 
| 
| Please report it as a compiler bug to
glasgow-haskell-bugs at haskell.org,
| or http://sourceforge.net/projects/ghc/.
| 
| make: *** [PluginAPI.o] Error 1
| 
| and this is the offending part of the code:
| 
| data HWSPlugin = (?access_log_chan:: Control.Concurrent.Chan.Chan
|   AccessLogger.LogRequest) => HWSPlugin
|     { pName               :: String
|     , pVersion            :: String
|     , pInit               :: Maybe InitFunc
|     , pURITransHandler    :: Maybe HandlerFunc                  --
one
|     , pAccessHandler      :: Maybe HandlerFunc                  --
all
|     , pAuthHandler        :: Maybe HandlerFunc                  --
one
|     , pMimeHandler        :: Maybe HandlerFunc                  --
one
|     , pFixupHandler       :: Maybe HandlerFunc                  --
all
|     , pContentHandlers    :: [(String,HandlerFunc)]             --
one
|     -- the line below requires the additional constraint
|     , pLogHandler         :: Maybe HandlerFunc                  --
all
|     }
| 
| I stumbled over this while experimenting with HWS-WP. More
specifically while
| trying to replace unsafePerformIO-style global variables with implicit
| parameters. The sources are fresh from CVS, the changes I made were
minimal
| (most of them to make everything compile with ghc-6.2.2). I can send a
tar
| file if that helps reproducing the problem.
| 
| Cheers,
| Ben
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