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On 15-Jan-06, at 7:25 PM, Chris Marrin wrote:

Since Lua has multiple return values, why not just always return errno as the second return value of each (relevant) call?

Fair enough. In that case, errno() is unnecessary (and not obviously implementable on non Posix systems).

POSIX (and Win32) standardize the names of the errno constants; I agree that these should be strings (just simple strings, like "ENOENT"; the WSA_ prefix can be deleted, for example, so that the names coincide. There's a errno translation mechanism in APR which you could stealxxxxrepurpose :) in general, I think looking at APR's API is a good idea because a lot of people have thought hard about how to make an API which is both portable and easy to use.

Just to explain my reasoning:

In order for functions which might be used as iterators to be usable as iterators, it is important that they return <false, error>, rather than <nil, error>. However, having thought about this a bit, and tried both interfaces, I actually remain convinced that being able to access errors "after the fact" leads to simpler code. It is certainly possible to write:

  for in, errmsg in f:lines() do
    if errmsg then
      -- handle the error
    -- handle the non-error case

but it requires every script to think about the possibility of errors in order to avoid a runtime type error (boolean used where a string is required.) Maybe that's not a bad thing, but in many cases it is actually ok to just let a loop die if an error is encountered. Furthermore, errmsg in the above is local to the for loop, which is also a trifle awkward.

I would rather not globalize the discussion into existing functionality. I just want to get some needed functions online ASAP!

Good point. Sorry. I'll try and focus my thoughts about filesystem interfaces for some other thread. :)