On Tue, Oct 15, 2019 at 10:15:34AM +0200, Hans Hagen wrote:
> On 10/15/2019 10:04 AM, Taco Hoekwater wrote:
> > Hi Rudolf,
> >
> > > On 15 Oct 2019, at 00:50, Rudolf Bahr <qu...@quasi.de> wrote:
> > >
> > > Now to your suggestion not to use "assert ()". Indeed it's a solution! My
> > > program
> > > works! I append again its output (again just for fun!). Did you really
> > > try it or
> > > has it been just an idea?
> >
> > First, let me say that embedded lua versions are typically a little bit
> > different
> > from standalone. Just how much different depends on the embedding program.
> > Luatex
> > is actually pretty close to standalone lua. Luatex adds a bunch of
> > extension libraries,
> > but it changes very little of the core language. And all those changes are
> > documented
> > in the luatex manual. None of those changes affect your minimal example,
> > except
> > that lua errors are handled a little differently.
> >
> > Note that standalone lua *also* produces an error, as that is what assert()
> > is
> > supposed to do. And when lua runs into an error, it ignores the rest of the
> > current
> > chunk:
> >
> > “... whenever an error occurs, Lua ends the current chunk and returns
> > to the application.” (from lua.org)
> >
> > Standalone lua typically sees only one chunk (the file you pass on the
> > command
> > line) but embedded lua implementation often see (sometimes many) more
> > chunks.
> > In luatex’s case, each \directlua is a separate chunk (in ConTeXt, that
> > means every
> > \startluacode block and every \ctxlua call is a separate chunk).
> >
> > The only unusual thing here is that standalone lua silently quits and
> > returns a
> > non-zero exit code to the shell, whereas luatex gives you the typical
> > TeX-style
> > error prompt. The rationale for that is: lua errors can happen in many
> > places in
> > your input file, and if they were silently ignored, your typeset pages
> > could be
> > wrong without you realising it.
> >
> >
> > And to answer your question above: I did not have to try or guess. I know
> > about
> > how assert() works because it is documented in the lua manual (and as it
> > closely
> > mimics the assert() C function, that is easy for me to remember).
> as you say, it's all normal lua behaviour:
>
> if you do:
>
> print(io.open("crap.crap"))
>
> one gets
>
> nil crap.crap: No such file or directory 2
>
> and i think that assert then returns the second returned argument
>
> but if one does
>
> context(io.open("crap.crap") and "yes" or "no")
>
> then the first argument is checked against
>
> Hans
Hi Hans, hi Taco!
For your answers and patient explanations I want to thank you, not to forget
[1], [2], [3] for instance! Now it gets clearer to me what the distinctive
features could be which one can encounter when using a combination of even so
wunderful programming languages as ConTeXt and Lua are!
Best wishes,
Rudolf
[1] https://wiki.contextgarden.net/Programming_in_LuaTeX
[2] http://www.luatex.org/svn/trunk/manual/luatex.pdf
[3] http://www.pragma-ade.com/general/manuals/cld-mkiv.pdf
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