status of rebindable syntax for arrows
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
On Tue, Oct 14, 2014 at 10:26:46PM +0200, S. Doaitse Swierstra wrote:
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.
It already has a bug entry: #7828. What would help is to know the kind of use you have in mind, to see whether it fits with the proposed solution.
| It already has a bug entry: #7828. What would help is to know the | kind of use you have in mind, to see whether it fits with the proposed | solution. Indeed. Moreover #7828 is stalled; it needs some arrow-savvy person to focus cycles on it. If rebindable syntax for arrows is considered important. Meanwhile I think you should not rely on rebindable syntax for arrows. The user manual is misleading on this point. Simon | -----Original Message----- | From: Glasgow-haskell-users [mailto:glasgow-haskell-users- | bounces@haskell.org] On Behalf Of Ross Paterson | Sent: 15 October 2014 06:56 | To: glasgow-haskell-users | Subject: Re: status of rebindable syntax for arrows | | On Tue, Oct 14, 2014 at 10:26:46PM +0200, S. Doaitse Swierstra wrote: | > 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. | | It already has a bug entry: #7828. What would help is to know the | kind of use you have in mind, to see whether it fits with the proposed | solution. | _______________________________________________ | Glasgow-haskell-users mailing list | Glasgow-haskell-users@haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
participants (3)
-
Ross Paterson -
S. Doaitse Swierstra -
Simon Peyton Jones