[GHC] #13467: ghc: panic! (the 'impossible' happened), initTc: unsolved constraints

22 Mar 2017


      #13467: ghc: panic! (the 'impossible' happened), initTc: unsolved constraints
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           Reporter:  jhjonsson         |             Owner:  (none)
               Type:  bug               |            Status:  new
           Priority:  normal            |         Milestone:
          Component:  Compiler          |           Version:  8.0.2
           Keywords:                    |  Operating System:  MacOS X
       Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
          Test Case:                    |        Blocked By:
           Blocking:                    |   Related Tickets:
Differential Rev(s):                    |         Wiki Page:
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 NB! I'm no expert on the compiler and have not used GHC/GHCi very much. I
 have istaller the Haskell Platform and then run GHCi from within Aquamacs
 (emacs) using tthe Haskell mode already available there. I should say that
 everything worked fine and I could both load and run code. But then this
 happend when I started with the type Char and the functions ord and chr,
 so maybe the error has to do with them(?) Please change the subject to
 something relevant; I really have no clue what has happened here. Just
 like to help. /Håkan
 ---
 This is the error message:

 "GHCi, version 8.0.2: http://www.haskell.org/ghc/  :? for help
 Prelude> :load "/Users/hj/Downloads/d7012e-vt17/test.hs"
 [1 of 1] Compiling Main             ( /Users/hj/Downloads/d7012e-
 vt17/test.hs, interpreted )
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.0.2 for x86_64-apple-darwin):
         initTc: unsolved constraints
   WC {wc_insol = [W] –_a2n2 :: t_a2n1[tau:1] (CHoleCan: –)}

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

 This is my Haskell code (putting together examples for a first lecture on
 declarative languages/functional languages):


 module Main (main) where
 import Data.Char (ord,chr)

 square :: Int -> Int
 square n = n * n

 primes :: [Int]
 primes = filterPrime [2..]
   where
     filterPrime (p:xs) =
        p : filterPrime [x | x <- xs, x `mod` p /= 0]

 -- take :: Int -> [a] -> [a]

 double :: Int -> Int
 double n = 2*n

 dubSq1 :: Int -> Int
 dubSq1 n = double (square n)

 dubSq2 :: Int -> Int
 dubSq2 = double . square

 -- Bool

 nAnd :: Bool -> Bool -> Bool
 nAnd x y = not (x && y)

 nAnd2 :: Bool -> Bool -> Bool
 nAnd2 True True = False
 nAnd2 False False = False
 nAnd2 x y = True

 -- if, the, else

 max2 :: Int -> Int -> Int
 max2 x y =
   if x >= y then x else y

 -- Int

 max3 :: Int -> Int -> Int -> Int
 max3 a b c = max2 (max2 a b) c

 f :: Int -> Int
 f 1 = 0
 f n = if  n `mod` 2 == 0 then n `div` 2 else 3*n + 1


 isDigit :: Char -> Bool
 isDigit ch = ('0' <= ch) && (ch <= '9')

 isLower :: Char -> Bool
 isLower ch = ('a' <= ch) && (ch <= 'z') -- no åäö in ASCII

 offset :: Int
 offset = ord 'A' – ord 'a'

 toUpper :: Char -> Char
 toUpper ch = chr (ord ch + offset)


 f' 1 = 0
 f' n
   | n `mod` 2 == 0 = n `div` 2
   | otherwise = 3*n + 1

 life_length x
   | x == 1 = 0
   | otherwise = 1 + life_length(f' x)

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13467
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler