[Haskell-cafe] Debugging partial functions by the rules

[Simon Peyton-Jones]

| I have always been wondering why error shouldn't always return a call
| stack from the occurrance of fromJust up to the function I typed into
| ghci (or up to main, for that matter).
|
| I guess this is because the call tree is rewritten extensively before
| being evaluated, and the output wouldn't be so easy to match to the
| source code?  But shouldn't the mapping of source tree to executable
| tree be bijective, at least in theory?

Simon and I have been brainstorming on just such a thing.   I've jotted down our current notes (well some of them) here
        http://hackage.haskell.org/trac/ghc/wiki/ExplicitCallStack

Simon