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- Subject: Re: Simple configurable expression parser (in pure Lua)
- From: Domingo Alvarez Duarte <mingodad@...>
- Date: Wed, 22 Jun 2022 13:14:36 +0200
Hello Lorenzo !
Could you publish what you have done so far ?
You've said that you usually distribute it to others, so why not show
then here ?
If people can see your usage then they could give you a better advice.
On 22/6/22 13:11, Lorenzo Donati wrote:
On 20/06/2022 08:03, Thijs Schreijer wrote:
On 14 Jun 2022, at 13:00, Luiz Henrique de Figueiredo
can it parse operators that are not Lua operators, i.e. can I define,
for example, a "&=" or "===" binary operator?
No, my code can only handle Lua syntax.
Not sure it is helpful, but Penlight has with a lexer;
Thanks for this pointer, Thijs.
Unfortunately it's not immediately useful in my use case (I need more
of a generic configurable parser, than a simple lexer).
However maybe I could hack it to make it work for my purposes
(depending on how contrived its code is).
The major obstacle for me it's the very limited time I have got to
dedicate to the effort.
My ad-hoc solutions work quite well. My problem is that I'm getting
used to this evil workflow:
1. Ok, I need to parse an expression (Lua/C/C++/Latex/etc.) and maybe
rewrite it in an "equivalent" (for some definition of equivalent) or
modified form in another language (Lua/C/C++/Latex). Or maybe I have
to generate a random expression (Lua/C/C++/Latex) of given
2. Mmmh, I think I did that before. Let's look at my older code. Ah!
Here it is something similar!
3. Copy-Modify-Paste and Test until it works.
All this because I've never found the time to consolidate all that
code (and probably I never will).
This is getting ludicrous and my "professional developer" brain hurt
any time I'm forced to do that. If it were for a couple of throwaway
script, meh!, who would care. The issue is this turns out to be a
often recurring problem.
Just to be more specific: I usually write the tests (or other
documents) for my students as LaTeX fragments (with embedded Lua code)
that a set of tools (written by me in Lua) put together to obtain the
final PDF for the test.
These tools have lots of useful functionalities, such as randomizing
the position of questions and answers and, upon further configuration,
also randomization of part of the content.
This allows me to produce a number of different versions of the same
test, but still maintaining its general content and difficulty level.
This is quite more efficient than using a simple word processor (even
in conjunction with embedded scripting), since through Lua+Latex I
have the power to render the document exactly as I want
programmatically, also handling complex mathematical notations or
electronic circuit schematics.
However, this has drawbacks: with every version I have a different
solution set, and during the correction phase it's just too easy to
mark the right answer as good or vice-versa. To save time I correct
them putting my brain in "dumb-but-quick" mode: I simply check them
against a "cue sheet" (specific for each version) with the right
answers that my tools automatically generate.
However that needs a way to enter some formulas in one language Syntax
(e.g. C), converting them to Lua for evaluation and then to Latex for
rendering. All this to avoid more failure points I would have if I had
to write the formulas in three different syntaxes manually.
Hope this helps framing the issue.