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Re: Scripting

From: Marco Gerards
Subject: Re: Scripting
Date: Sun, 13 Feb 2005 18:56:16 +0000
User-agent: Gnus/5.1006 (Gnus v5.10.6) Emacs/21.3 (gnu/linux)

Serbinenko Vladimir <address@hidden> writes:

>>- Why does everything happen with strings?
> Because environment variables are the strings and it's not really
> needed to convert them (excluding the calculating)

Personally I don't like it too much.  I prefer keeping such
information in a struct or so.  You could how it in a string, but in
that case I would not use string operations that much.

>>- Why are that many functions duplicated? (for example
>>  grub_bash_dupstr).
> In this case I just forgot about grub_strdup. But some other functions
> have (nerly) the same names that string function but are adapted for
> scripting (ex: grub_bash_strchr)

What is the difference with grub_strchr and grub_bash_strchr?  The
names give me the impression they are similar.

One this about the `grub_bash_' prefix.  I think it is a bit confusing
because the syntax is bash like, it is not bash.  I would prefer a
grub_script_ or grub_scripting_ prefix.

>> - What is that huge table with operators?
> It's used to determinate which operator to execute (see
> grub_bash_find_oper and grub_bash_eval_arith)


>>What kind of parser is it?
> It's a direct parser with aritmetic subparser. Main parser is
> grub_bash_execute, arithmetic subparser is grub_bash_eval_arith.
> grub_bash_execute determinates the special cases (loops,conditions,
> functions,...) for other cases (commands,assignments, function calling)
> it calls grub_bash_split_tokens, grub_bash_expand_braces and
> grub_bash_expand_dollar
>>  I have never seen this in a top-down or bottom-up parser I have
>>  studied.
> I don't like to write the things reffering every time to algorithm.
> Genereally I take some ideas and I write myself, at my own.

What do you mean?

The problem is that I like proven concepts.  And when you use a
commonly known parser design many people will be able to understand
it.  To me this is REALLY important.  I wonder what other developers
think of that.

>>So can you explain what
>>  happens when executing a script?  First you load the file.  Do you
>>  parse it, make pcode of it, run it directly?
> For the files I use grub_bash_exec_file. Only thing it does is
> reading a file line by line and calling grub_bash_execute

So you run it while parsing, ok.

>>  How about error
>>  handling?
> For now the problem is that not all posiible syntax errors are handled
> correctly and more return checks have to be written. But first I'll write
> line counting (only grub_bash_execute, grub_bash_list_execute and
> grub_command_execute are affected)

Ok.  Error handling is often not implemented in small parsers because
it can be really hard.  Don't forget error handling is really
important.  Syntax errors should not make the parser crash, hang,
etc.  Producing the right error and handling it right so GRUB remains
in a valid state, etc is a difficult task, I think.


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