Re: Exception handling (was Re: ...add to Lua...)

[Dirk Laurie <dirk.laurie@...>]

Op Ma., 17 Sep. 2018 om 09:36 het Sean Conner <sean@conman.org> geskryf:
>
> It was thus said that the Great Dirk Laurie once state
> >
> > That single ^NOT, appearing in a non-monospaced font, correcting a
> > sentence starting "Personally" (which usually means that, in the
> > opinion of the author, a non-PC point of view will follow) makes it
> > totally impossible to figure out what you are trying to convey.
>
>   I messed that up (I can't read today---it was fine as it was originally).

I'm not quoting your good, clear explanation, but would urge readers
whose mail clients are good enough to reread it.

>   Now, on to your questions ...
>
> > Do you basically agree that
> >
> > (a) languages usually run from an interpreter or a host program (as
> > Lua is) should offer (as Lua does) three abnormal exits from a
> > program:
>
>   What do you mean by "program?" [8]
...
> What do you mean by "host?"

As used the Lua manual: "Lua ... works embedded in a host client,
called the embedding program or simply the host."

> Because my definition is the same as "system", which you list below.

I was hoping that my footnotes, giving the corresponding Lua
functions, would make that clear.

> > [1] In Lua, by way of type and number of return values, especially
> > "false, message"'
> > [2] In Lua, by way of error())
> > [3] In Lua, by way of os.exit()
> > [4] In Lua, by way of pcall()

But let's try again.

Level 0    Operating system (whether shell or GUI)
Level 1    Invokes a command or starts an application called "lua",
"python", "perl", "ruby", "js", "apl", "love", "luatex" etc.
Level 2    which invokes code written in a 'scripting" language
Level 3    which calls a function
Level 4    which calls a function
...
Level n    which encounters a condition that makes it impossible to go
on as normal.

Now from level n, Lua code can say: return to level  0 (bypassing all
finalizers not regestered at that level) or return to level 1
(allowing various sorts of recovery) or drop down to level n-1
(passing the buck). In addidition, Level n-1 may disallow a direct
return to Level 1.

The questions to agree or disagree on are:

(a) All languages that involve at least Levels 0,1,2 should offer all
those options.
(b) Very few except Lua actually offer that.

> [9]     I wrote about it a bit here:
>
>                 http://boston.conman.org/2009/12/01.2
>
>         (near the bottom)---I classified four categories for errors, along
>         with three ways of handling them, but I've thought hard about that
>         since then and modified my position somewhat (two two ways of
>         handling errors).

I think I understand both that post and your explanation of the 2x2
position, but it will require a chain of deductions to move from there
to answers to my questions, and I don't wish to second-guess you :-)

-- Dirk