It may be a bug in ghc.  It may be a bug in stack.  Not much you can do about it other than to report it.

On Mon, Dec 11, 2017 at 11:39 AM, Baa <aquagnu@gmail.com> wrote:

Hello, List. I hit error:

    ghc: panic! (the 'impossible' happened)
      (GHC version 8.0.2 for x86_64-unknown-linux):
        initTc: unsolved constraints
      WC {wc_insol = [W] spec_a86e :: t_a86d[tau:1] (CHoleCan: spec)}

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

what does it mean and how to fix it?

PS. I only added template Haskell "call" in my test suite like

  $(blahBlah something)

The same call works fine in other modules and in GHCI. "stack build"
works too, but tests - no (last stack 1.6.1)

===
Best regards, Paul
_______________________________________________
Beginners mailing list
Beginners@haskell.org
http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners