[GHC] #1223: ghc-6.6: panic! (the 'impossible' happened)

[GHC]

#1223: ghc-6.6: panic! (the 'impossible' happened)
-------------------------------+--------------------------------------------
 Reporter:  jupdike at gmail.com  |          Owner:         
     Type:  bug                |         Status:  closed 
 Priority:  normal             |      Milestone:         
Component:  Compiler           |        Version:  6.6    
 Severity:  normal             |     Resolution:  fixed  
 Keywords:                     |     Difficulty:  Unknown
 Testcase:                     |   Architecture:  x86    
       Os:  MacOS X            |  
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Changes (by simonpj):

  * resolution:  => fixed
  * status:  new => closed

Comment:

 OK I've looked into this.  I boiled it down a bit to a single file (see
 new below).

 The problem turned out to be something to do with "linear implicit
 parameters", which are a heavily deprecated feature of GHC 6.6, and are
 removed altogether in the HEAD.  In Era.hs we find things like "1%n", and
 the "%n" was interpreted as a linear implicit parameter.

 Of course this still should not trigger a crash.

 The 6.6 release notes advertised the linear implicit parameters might well
 vanish from 6.6.1, and this seems a good moment to do so.  I'm going to
 take them out of the parser only.

 I'll patch the branch directly; the HEAD is fine.

 Simon

 Here's my cut-down code:
 {{{
 module Era where

 import Ratio
 import Char
 import Numeric (readDec, readSigned)

 data CR = CR_ (Int -> Integer)

 instance Eq  CR where
 instance Show  CR where
 instance Ord CR where
 instance Num CR where
 instance Fractional CR where
 instance Floating CR where

 log_drx :: CR -> CR
 log_drx = power_series [1%n | n <- [1..]] (+1)

 acc_seq :: (Rational -> Integer -> Rational) -> [Rational]
 acc_seq f = scanl f (1%1) [1..]

 exp_dr :: CR -> CR
 exp_dr = power_series (acc_seq (\a n -> a*(1%n))) id


 power_series :: [Rational] -> (Int -> Int) -> CR -> CR
 power_series = error "urk"
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1223>
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