[Haskell-cafe] RFC: rewrite-with-location proposal

[Alberto G. Corona]

Additionally, Another  way to include line number information and to
improve readability of the degugging code  is to add "verify"  as an
 "assert" with flipped parameters so we can write:

let x= head xs                 `verify` (not $ null xs)

So the assertions appear on the right , separated from the  rest of the
code.

instead of

let x= assert (not $ null xs) xs





2013/2/26 Gershom Bazerman <gershomb at gmail.com>

>  On 2/25/13 9:42 AM, Simon Peyton-Jones wrote:
>
>  I’m afraid the rewrite-rule idea won’t work.  RULES are applied during
> optimisation, when tons of inlining has happened and the program has been
> shaken around a lot. No reliable source location information is available
> there.****
>
> ** **
>
> See http://hackage.haskell.org/trac/ghc/wiki/ExplicitCallStack; and
> please edit it.****
>
> ** **
>
> One idea I had, which that page does not yet describe, is to have an
> implicit parameter,
> something like ?loc::Location, with****
>
>           errLoc :: ?loc:Location => String -> a****
>
>           errLoc s = error (“At “ ++ ?loc ++ “\n” ++ s)****
>
> ** **
>
> This behave exactly like an ordinary implicit parameter, EXCEPT that if
> there is no binding for ?loc::Location, then the current location is used.
> Thus
>
>
> I like the general approach of this proposal quite a bit. I'd very much
> like Location to be not just a string, but a record type. Ideally we could
> recover not just module name, line and character, but also the name of the
> function that takes the location. This would eliminate an entire swath of
> use-cases for Template Haskell. For example, I've worked out a
> template-haskell-free version of the Cloud Haskell closure API, which
> hopefully is getting merged in at some point. The major drawback it has is
> that the user is required to provide a globally-unique identifier for each
> closure, ideally stable across compilations. The current TH code solves
> this by grabbing the function and module name. If we could get direct
> access to these things without requiring template haskell, that would be
> quite nice. Other types of RPC libraries I've worked on could similarly
> benefit from this.
>
> Cheers,
> Gershom
>
>
>
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>


-- 
Alberto.
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