#14963: ghci -fdefer-type-errors can't run IO action from another module -------------------------------------+------------------------------------- Reporter: elaforge | Owner: tdammers Type: bug | Status: new Priority: high | Milestone: 8.4.2 Component: GHCi | Version: 8.4.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by tdammers): Replying to [comment:22 tdammers]:
As discussed in Hangouts, the problem is even more specific: it only appears for expressions entered at the GHCi prompt while defer-type-errors is active. Loading modules with defer-type-errors on, then turning it off and *then* evaluating expressions at the prompt works just fine.
It actually turns out that this isn't the case, as the following sample GHCi session illustrates: {{{ tobias@zoidberg:~/well-typed/devel/ghc-disable-defer-type-errors/ > ghc --interactive Foo.hs -fdefer-type-errors GHCi, version 8.4.1: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/tobias/dotfiles/ghc/.ghc/ghci.conf [1 of 1] Compiling Main ( Foo.hs, interpreted ) Ok, one module loaded. λ> test ghc: panic! (the 'impossible' happened) (GHC version 8.4.1 for x86_64-unknown-linux): nameModule system $dShow_a22M Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable pprPanic, called at compiler/basicTypes/Name.hs:241:3 in ghc:Name Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug λ> :set -fno-defer-type-errors λ> test ghc: panic! (the 'impossible' happened) (GHC version 8.4.1 for x86_64-unknown-linux): nameModule system $dShow_a289 Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable pprPanic, called at compiler/basicTypes/Name.hs:241:3 in ghc:Name Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} However this probably just means that `:set` doesn't properly unset the `fdefer-type-errors` flag. Hmm. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14963#comment:23 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler