#8659 closed bug (duplicate)

GHCi told me to tell you that it crashed

Reported by: ishkabible Owned by:
Priority: normal Milestone:
Component: GHCi Version: 7.4.2
Keywords: Cc: hvr
Operating System: Unknown/Multiple Architecture: x86
Type of failure: None/Unknown Test Case:
Blocked By: Blocking:
Related Tickets: Differential Rev(s):
Wiki Page:


I'm using an x86 build of GHCi version 7.4.2 on Windows 7 professional.

I attempted to interpret the following code and GHC crashed and told me to report the issue.

module ConstructorTypes where

import Data.List (intercalate)
import VarGenMonad

data ConstructorSpec = Spec {
    parrentType :: ConstructorSpec,
    specName :: String,
    specArgs :: [Type] 
} deriving(Eq, Ord)

data ConstructorTypeSpec = ConTypeSpec { conTypeName :: String, conSpecs :: [ConstructorSpec], numParams :: Int }

data Pattern = Pat ConstructorSpec [Pattern]
             | Id String
    deriving(Eq, Ord)

--this holds
data Type = Poly Type
          | DeBruijnTypeVar Int
          | ConType ConstructorTypeSpec
          | Type :-> Type
    deriving(Eq, Ord, show)

--define Eq and Ord to break infinte chain of type/spec/type/spec/...
instance Eq ConstructorTypeSpec where
    t1 == t2 = conTypeName t1 == conTypeName t2

instance Ord ConstructorTypeSpec where
    t1 <= t2 = conTypeName t1 <= conTypeName t2

--create own show types to give a nice syntax and avoid infinite loops
instance Show ConstructorSpec where
    show (Spec ty name args) = name ++ (concatMap ((' ':) . show) args) ++ " :: " ++ conTypeName ty

instance Show ConstructorTypeSpec where
    show (ConTypeSpec name specs vars) = name ++ "=" ++ (concatMap (("\n\t" ++) . show) specs)

genUniqueVars lst n = take n $ runVarGen lst gen
    where gen = do
              x <- drawVar
              return $ x : gen

toString env (Poly t) = do
    a <- drawVar            --should advance to next varible
    b <- toString (a:env) t --any calls to drawVar in toString should advance it as well
    return $ "(forall " ++ a ++ ")" ++ b
toString env (DeBruijn x) = do
    return $ env !! x       --no changes are made here however
toString env (ConType spec) = do
    names <- mapM_ (toString env) (typeVars spec) --each call to drawVar in each call toString should advance the internal state 
    return $ conTypeName spec ++ intercalate " " names
toString env (x :-> y) = do
    t1 <- toString env x
    t2 <- toString env y
    return $ "(" ++ t1 ++ ") -> " ++ t2

"VarGenMonad" is the following code

module VarGenMonad (VarGen, runVarGen, runVarGenWith, drawVar) where

import Control.Monad

--effectivlly a state monad of type State a [String]
newtype VarGen a = VarGen { getFunc :: [String] -> (a, [String]) }

--just gets the resulting value (this is what users will interface to)
runVarGen vl vg = runVarGenWith showInt
    where showInt 0 = ""
          showInt x = show x

--another function the user can interacte with
runVarGenWith f vl vg = fst $ runState vg (makeVarListWith f vl)

--gets the result from a var gen monad after telling it what varibles to use
runState :: VarGen a -> [String] -> (a, [String])
runState vg vl = (getFunc vg) vl

--creates an infinte list of unique varibles from a finite one
makeVarListWith :: Integral a => (a -> String) -> [String] -> [String]
makeVarListWith f lst = gen lst lst 0
    where gen t []     c = gen t t (c + 1)
          gen t (x:xs) c = (x ++ f c) : gen t xs c

--implements the monad operations in same fashion as a state monad
instance Monad VarGen where
    return x = VarGen $ \s -> (x, s)
    cur >>= transform = VarGen func
        where func s = runState (transform v) nextList
                  where (v, nextList) = runState cur s

drawVar :: VarGen String
drawVar = VarGen $ \(x:xs) -> (x, xs)

this worked before I added "show" (note that it is lowercase cuz I messed up) to the deriving cluase of my 'Type' type. After fixing it to make it an upper case S GHC promptly told me what else I had messed up in my code (that is, it worked correctly).

Change History (1)

comment:1 Changed 23 months ago by goldfire

  • Resolution set to duplicate
  • Status changed from new to closed

This is already fixed in GHC 7.6.3 and in HEAD.

Thanks for reporting!

Note: See TracTickets for help on using tickets.