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- Subject: Re: [proposal] debug.geterrfunc to get current error function
- From: GrayFace <sergroj@...>
- Date: Wed, 22 Feb 2012 01:44:53 +0700
I agree, being able to call pcall with the same error function would be
useful in any case.
As for the thing that I wanted, I gave it more thought and here's an
idea I came up with:
I think it would be good to implement try,except,finally in a fashion
orthogonal to pcall. It won't be as powerful as try,except,finally in
other languages, because 'except' won't be able to recover execution.
It's pretty much implementation-driven, but first here's the approximate
syntax in two cases of interest:
1) Adding additional info to error message:
for i = 1,100 do
errorinfo.text = tostring(errorinfo.text).." (i = "..i..")"
error("Oops") -- do something here
except() -- 'except' function closes the Try block
local f = assert(io.open("c:/error.txt", "r"))
The error handler is passed to try() function and the protected code
goes after it as plain code, not as another function (as in case of
using pcall for similar goals). try() set up an error handler that would
be called in case of an error. except() removes the error handler from
handlers list, finally() executes the error handler and removes it.
These 2 functions return all arguments they receive, so that one would
easily write "return except(5)".
The order in which the handlers are executed is the opposite of the
order in which they are set up with the pcall error function executing last.
I already have an implementation plan, it would be pretty simple. The
usage seems relatively convenient, but the syntax is unusual and you
must take care of executing except/finally, e.g. if you want to use
'return' inside the first example's Try block, you'll have to turn it
into 'return except()'.
Sergey Rozhenko mailto:email@example.com