Thanks Roberto! Roberto Zunino wrote:

Chris Kuklewicz wrote:

...

There is no way to create a "A.hs-boot" file that has all of (1) Allows A.hs-boot to be compiled without compiling B.hs first (2) Allows B.hs (with a {-# SOURCE #-} pragma) to be compiled after A.hs-boot (3) Allows A.hs to compiled after A.hs-boot with a consistent interface

I thought the following A.hs-boot would suffice:

module A(A) where data A

There's no need to provide the data constructors for type A. Does this violate any of the goals above?

Regards, Zun.

I tried that experiment. The failure is complicated, and triggers be a ghc bug. Hmmm... the bug for

module A(A) where data A deriving Show

using "ghc -c -XGeneralizedNewtypeDeriving A.hs-boot" is

A.hs-boot:2:0:ghc-6.8.3: panic! (the 'impossible' happened) (GHC version 6.8.3 for powerpc-apple-darwin): newTyConEtadRhs main:A.A{tc r5z}

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

Is this a known bug? But now I see that

module A(A(..)) where import B(B) data A = A B | End deriving Show

does work. And avoids the bug! -- Chris