id,summary,reporter,owner,description,type,status,priority,milestone,component,version,resolution,keywords,cc,os,architecture,failure,difficulty,testcase,blockedby,blocking,related
7199,Standalone deriving Show at GHCi prompt causes divergence when printing,dpmulligan,,"Deriving a show instance for a data type (defined either with the standard Haskell 98 syntax or with GADT syntax) within GHCi using the command:
  
{{{
instance Show <typename>
}}}

causes divergence/stack overflow when printing values of that type.  The issue does not manifest itself when you use the standard deriving mechanism within a Haskell source file.

Minimum example necessary to replicate:

{{{
module Main (
  main
)
where

  -- At GHCi prompt type
  --   instance Show Bool'
  -- then
  --   True'
  -- to get a stack overflow
  data Bool'
    = True'
    | False'

  main = return ()
}}}",bug,closed,normal,,GHCi,7.4.1,invalid,"deriving, divergence, ghci",,Linux,x86,GHCi crash,Unknown,,,,