#2880: GHC panic when printing Unique
------------------------------+---------------------------------------------
Reporter: sebf | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 6.10.1
Severity: normal | Resolution:
Keywords: | Testcase:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
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Comment (by batterseapower):
I don't think this is actually a bug. Printing a Unique actually does
require access to the static flags, so you need to initialize them as the
panic suggests.
The relevant code is in Unique.lhs:
{{{
pprUnique :: Unique -> SDoc
pprUnique uniq
| opt_SuppressUniques
= empty -- Used exclusively to suppress uniques so you
| otherwise -- can compare output easily
= case unpkUnique uniq of
(tag, u) -> finish_ppr tag u (text (iToBase62 u))
}}}
Note the use of opt_SuppressUniques, a static flag, which pulls on the
staticFlags thunk and hence causes the panic.
I'm not sure we actually intend UniqSupply et al. to be used outside the
context of GHC session, so this behaviour does not surprise me...
You can probably fix it by doing:
{{{
import UniqSupply
import StaticFlagParser (parseStaticFlags)
main = do
parseStaticFlags []
mkSplitUniqSupply 'x' >>= print . uniqFromSupply
}}}
This will most likely continue to work in the future, but there are no
guarantees :-)
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2880#comment:1>
GHC <http://www.haskell.org/ghc/>
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