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
_______________________________________________
Haskell-Cafe mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/haskell-cafe
