Bug while writing a simple parser with Parsec

module Main where

import Control.Monad.Identity
import Control.Monad.State
import Data.List
import Text.ParserCombinators.Parsec

type Name = String

data Value = VlInt Int | VlBool Bool deriving Show

data Term =
  TmVal Value
  | TmVar Name
  | TmLet Name Term Term
  | TmAdd Term Term
  deriving Show

parseTerm :: Parser Term
parseTerm = parseVal <|> parseVar <|> parseLet <|> parseAdd

And then I get:

GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( Main.hs, interpreted ) ghc: panic! (the 'impossible' happened)

(GHC version 8.0.2 for x86_64-unknown-linux):

initTc: unsolved constraints

WC {wc_insol =

\[W\] parseVal_a2YR	t_a2YQ\[tau:1\] (CHoleCan: parseVal)
\[W\] parseVar_a2YY	t_a2YX\[tau:1\] (CHoleCan: parseVar)
\[W\] parseLet_a2Z5	t_a2Z4\[tau:1\] (CHoleCan: parseLet)
\[W\] parseAdd_a2Z8	t_a2Z7\[tau:1\] (CHoleCan: parseAdd)}

Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug

Trac metadata

Trac field	Value
Version	8.0.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
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Operating system
Architecture

changed milestone to %8.6.1

changed weight to 5

added Tbug Trac import labels

closed

Thank you for the report. This has been fixed in GHC 8.2: #13106 (closed).

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedDuplicate

added Pnormal label