Parsing custom query language and query Ecto database

I’d highly suggest checking out GitHub - dashbitco/nimble_csv: A simple and fast CSV parsing and dumping library for Elixir · GitHub as far as parsing goes.

Hmmmmm I think maybe @benwilson512 meant nimble_parsec. Which would be good for this project, more expressive and easier to debug than leex and yecc.

Oops, I did!

Wouldn’t leex/yecc mean writing less code and maybe be faster?

having seen the tiny examples in nimble_parsec, and being comfortable with the lex+yacc combination in C and Python, yes, I have this same impression.

Consider the leex and yecc packages in the OTP standard library:

Less code: yes, I would agree with that (I’ve done a reasonable amount of work in leex/yecc and with nimble_parsec).

Faster: Not sure I agree. Theres some strong sub-binary optiimization in nimble_parsec too, but for sure it would require proper testing of like for like to decide. Or someone more qualified in both approaches than me,

If one has been done the learning curve of leex/yecc or their even more ancient cousins then they are certainly straight forward to use (although I do find removing shift/reduce errors/warnings less than obvious sometimes).

All said, thats why hoped to indicate that if one is getting into parsing for the first time then parse combinators are more approachable and, in my opinion, easier to debug.

so, I’m a few steps further. keep in mind that I already had the grammar, I only need the elixir/erlang code associated to the productions.

“a few steps further”, meaning I can parse stuff like "accession where taxon.rank.id=4", into {:where, {:domain, 'accession'}, {{:operator, :cmp_eq}, ['taxon', 'rank', 'id'], 4}}

and if you want to criticize my code to pieces, you’re most welcome! it’s as said on github.

now my question was, I come from object oriented C++ / Python, and my result of parsing would be an object which can execute tasks. in this case, it would be a database query, to which I would ask, please, the count, or again please, all the matching database records.

how would I proceed now, am not so sure, possibly just two count and add functions, defined by pattern matching, and I only need to find out how to manage the Ecto functions.

You should look at Filtrex, it runs ecto queries from a map of filters.
I used it in one of my project. You could also look at Forage, Mandarin + Forage - An admin tool for phoenix, it seems to be more powerful, there is no documentation but you could ask some help to the author. He answered quickly to my questions.

thank you for the hint, I had an extremely quick look (at Filtrex) … is it so that these filters only have intersect? and not union - exclusion? I’ll check with more time tomorrow or so. anyway looks like an interesting point, thank you.