Type deduction panic
> {-# LANGUAGE DeriveFunctor #-}
> module Bug where
> import qualified Data.Set as S
> import Data.Foldable (fold, foldMap, toList)
> import Data.List.Split (splitOn)
> import Data.Monoid -- ((<>), Sum, mempty, mappend)
> import Data.Functor.Foldable
> newtype Component = Component (Int,Int) deriving (Eq, Ord, Show)
> data Day24State v a = Day24State {
> valueToMatch :: Int,
> componentsToUse :: S.Set Component,
> componentMetric :: v,
> nextStates :: [a]
> } deriving (Functor, Show)
> type Day24StateFix v a = Fix (Day24State v) Now in GHCI type
:t Data.Functor.Foldable.ana f (undefined :: Day24StateFix Component)
Produces
ghc.EXE: panic! (the 'impossible' happened)
(GHC version 8.0.2 for x86_64-unknown-mingw32):
initTc: unsolved constraints WC {wc_insol = [W] f_akbJ :: t_akbI[tau:3] (CHoleCan: f)}
Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
Trac metadata
| Trac field | Value |
|---|---|
| Version | 8.2.2 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |