status of rebindable syntax for arrows

[S. Doaitse Swierstra]

The GHC manual already for quite a number of version states:

	• Arrow notation (see Section 7.17, “Arrow notation ”) uses whatever arr, (>>>), first, app, (|||) and loop functions are in scope. 
         But unlike the other constructs, the types of these functions must match the Prelude types very closely. Details are in flux; if you want to use this, ask! 

When using this feature we get the error:

"Var/Type length mismatch: 
   [s{tv aVL} [tv]]
   []
ghc: panic! (the 'impossible' happened)
 (GHC version 7.8.3 for x86_64-apple-darwin):
	tcTyVarDetails s{tv aVL} [tv]

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

So our question is whether we should really report this as a bug, and/or what we can do about this. 

Thanks for your help,

Doaitse