Re: [GHC] #1651: panic when interactively evaluating expression with a family type
#1651: panic when interactively evaluating expression with a family type +--- Reporter: chak |Owner: Type: bug | Status: closed Priority: normal |Milestone: Component: Compiler (Type checker) | Version: 6.7 Severity: normal | Resolution: fixed Keywords: | Difficulty: Unknown Os: Unknown | Testcase: Architecture: Unknown | +--- Changes (by chak): * resolution: = fixed * status: new = closed -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/1651 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #1651: panic when interactively evaluating expression with a family type
#1651: panic when interactively evaluating expression with a family type +--- Reporter: chak |Owner: Type: bug | Status: new Priority: normal |Milestone: Component: Compiler (Type checker) | Version: 6.7 Severity: normal | Resolution: Keywords: | Difficulty: Unknown Os: Unknown | Testcase: Architecture: Unknown | +--- Comment (by chak): Fixed the panic as per SimonPJ's suggestion. The bogus missing instance error remains to be corrected. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/1651 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #1651: panic when interactively evaluating expression with a family type
#1651: panic when interactively evaluating expression with a family type
+---
Reporter: chak |Owner:
Type: bug | Status: new
Priority: normal |Milestone:
Component: Compiler (Type checker) | Version: 6.7
Severity: normal | Resolution:
Keywords: | Difficulty: Unknown
Os: Unknown | Testcase:
Architecture: Unknown |
+---
Comment (by simonpj):
Hmm. Here's a FD version:
{{{
foo 'x'
where
foo :: C a b = a - b
class C a b | a - b
instance C Char Bool
}}}
The call `(tcMonoExpr (foo 'x') box)`
will perform a subsumption check `b = box`
and that will fill the box with a `TauTv`.
So what's missing is that when we defer we should fill `BoxTvs` with
`TauTvs`. I think that it'd be enough to call `unBox` instead of
`zonkTcType` in defer_unification.
Don't invest too much in this. I'm working with Dimitrios on rejigging
the whole over-complicated boxy-type story.
Simon
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/1651
GHC http://www.haskell.org/ghc/
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[GHC] #1651: panic when interactively evaluating expression with a family type
#1651: panic when interactively evaluating expression with a family type
--+-
Reporter: chak | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler (Type checker) |Version: 6.7
Severity: normal | Keywords:
Difficulty: Unknown | Os: Unknown
Testcase: | Architecture: Unknown
--+-
{{{
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE EmptyDataDecls #-}
newtype Succ a = Succ a deriving Show
dataZero = Zero
instance Show Zero where show _ = Zero
type family Add a b
type instance Add Zero a = a
type instance Add (Succ n) m = Succ (Add n m)
add :: a - b - Add a b
add = undefined
okay = show $ add Zero Zero
bad = add Zero Zero
{- ghci transcript:
*Main okay
Zero
*Main bad
ghc-6.7.20070828: panic! (the 'impossible' happened)
(GHC version 6.7.20070828 for i386-unknown-linux):
readFilledBox t_a1D9{tv} [box]
Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
*Main show bad
interactive:1:0:
No instance for (Show (Add Zero Zero))
arising from a use of `show' at interactive:1:0-7
Possible fix:
add an instance declaration for (Show (Add Zero Zero))
In the expression: show bad
In the definition of `it': it = show bad
-}
}}}
The panic arises as follows: `tcGhciStmts` calls `TcMatches.tcDoStmt` to
type check `it - bad`, which in turn evaluates
{{{
withBox liftedTypeKind $ \ pat_ty -
tcMonoExpr rhs (mkAppTy m_ty pat_ty)
}}}
The `withBox` executes the `readfilledBox` that causes the panic, as
`tcMonoExpr` promises to fill the boxes in its second argument. This
promise is not fulfilled, as `tcMonoBox` defers the match `Add Zero Zero ~
IO t_ayP`.
Further up the call chain `tcGhciStmts` will eventually simplify the LIE
and would discover the type mismatch (and hence abandon Plan A, of which
all this is part). Unfortunately, we never get there due to `withBox`s
attempt to read `t_avP`.
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/1651
GHC http://www.haskell.org/ghc/
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Re: [GHC] #1651: panic when interactively evaluating expression with a family type
#1651: panic when interactively evaluating expression with a family type +--- Reporter: chak |Owner: Type: bug | Status: new Priority: normal |Milestone: Component: Compiler (Type checker) | Version: 6.7 Severity: normal | Resolution: Keywords: | Difficulty: Unknown Os: Unknown | Testcase: Architecture: Unknown | +--- Comment (by chak): BTW, this bug was reported (and the example provided) by sjanssen from #haskell. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/1651 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
