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

On Mon, Feb 25, 2013 at 2:15 PM, Alexander Kjeldaas < alexander.kjeldaas@gmail.com> wrote:

On Mon, Feb 25, 2013 at 12:46 PM, Simon Hengel wrote:

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On Mon, Feb 25, 2013 at 10:40:29AM +0100, Twan van Laarhoven wrote:

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I think there is no need to have a separate REWRITE_WITH_LOCATION rule. What if the compiler instead rewrites 'currentLocation' to the current location? Then you'd just define the rule:

{-# REWRITE "errorLoc" error = errorLoc currentLocation #-}

REWRITE rules are only enabled with -O. Source locations are also useful during development (when you care more about compilation time than efficient code and hence use -O0). So I'm not sure whether it's a good idea to lump those two things together.

I could imagine that source locations being useful when debugging rewrite rules for example.

I think your argument makes sense, but why not fix that specifically?

{-# REWRITE ALWAYS "errorLoc" error = errorLoc currentLocation #-}

At that point, we've now made two changes to REWRITE rules: 1. They can takes a new ALWAYS parameters. 2. There's a new, special identifier currentLocation available. What would be the advantage is of that approach versus introducing a single new REWRITE_WITH_LOCATION pragma? Michael