id,summary,reporter,owner,description,type,status,priority,milestone,component,version,resolution,keywords,cc,os,architecture,failure,difficulty,testcase,blockedby,blocking,related
1513,odd panic with [()] >>> (),scook0@…,,"While messing around with arrows in GHCi, I was surprised to see the following (ill-typed) code cause a panic:

{{{
   ___         ___ _
  / _ \ /\  /\/ __(_)
 / /_\// /_/ / /  | |      GHC Interactive, version 6.6, for Haskell 98.
/ /_\\/ __  / /___| |      http://www.haskell.org/ghc/
\____/\/ /_/\____/|_|      Type :? for help.

Loading package base ... linking ... done.
Prelude> :m Control.Arrow
Prelude Control.Arrow> [1, 2] >>> pure (+1)
ghc-6.6: panic! (the 'impossible' happened)
  (GHC version 6.6 for i386-unknown-linux):
        nameModule it{v aIS}

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
}}}

Further experimentation revealed that
{{{
[] >>> ()
}}}
is a type-error as expected, whereas
{{{
[()] >>> ()
}}}
causes a panic.",bug,closed,normal,,Compiler,6.6,fixed,panic,,Linux,x86,,Unknown,,,,