status of rebindable syntax for arrows

S. Doaitse Swierstra doaitse at
Tue Oct 14 20:26:46 UTC 2014

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:"

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,


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