#7199: Standalone deriving Show at GHCi prompt causes divergence when printing
------------------------+---------------------------------------------------
Reporter: dpmulligan | Owner:
Type: bug | Status: new
Priority: normal | Component: GHCi
Version: 7.4.1 | Keywords: deriving, divergence, ghci
Os: Linux | Architecture: x86
Failure: GHCi crash | Testcase:
Blockedby: | Blocking:
Related: |
------------------------+---------------------------------------------------
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 ()
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7199>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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