[Haskell-cafe] Debugging partial functions by the rules

[Claus Reinke]

>    Couldn't we just use rewrite rules to rewrite *transparently*
>    all uses of fromJust to safeFromJust, tagging the call site
>    with a location?
.. 
> Looks good! But that is deceiving: the assert was expanded before the rule
> fired, and refers to the rewrite rule source line (line 19), not the fromJust
> call site (line 12).  Now if we could just have the 'assert' token inserted
> into the AST before it was expanded, we'd be home and dry. Could this be done
> with TH? Or could we arrange for asserts in rewrite rules not to be expanded
> till later?
.. 
> Any ideas?

http://www.haskell.org/pipermail/glasgow-haskell-users/2006-November/011545.html

claus