Evaluating undefined should return line number and module of location of undefined

[iampure@…]

Evaluating undefined should return line number and module of location of undefined when no optimizations are enabled.

[igloo]

The problem is that it's hard to do in a non-adhoc fashion. You can't just define

undefined :: a
undefined = "Undefined in " ++ magicIn ++ " at " ++ magicLocation

as that will just tell you something like "Undefined in undefined at GHC.Base line 15".

You can hack it up with CPP's LINE, but that's a bit nasty.

It would be possible to have a Template Haskell function that you'd use like

foo _ = $mkUndefined

except it doesn't look like we currently have a TH primitive to get the splice lication.

[simonpj]

See also  http://hackage.haskell.org/trac/ghc/wiki/ExplicitCallStack

[simonmar]

We could give undefined the same treatment that assert currently gets, that wouldn't be hard and addresses the original complaint.

[SamB]

This sounds like John Meacham's "magic underscore" (see  the JHC documentation).

Then again, it also reminds me of the Haskell 98 report (see just above  undefined's definition)

[igloo]

Duplicate of #960