esqueleto VS parsec

Writing Haskell programs that rely on third-party packages is still an issue when it’s a not actively maintained package. They get out of date with the base library (Haskell’s standard library), and you might see yourself in a situation where you need to downgrade to an older version. This is not exclusive to Haskell, but it happens more often than I’d like to assume. However, if you only rely on known well-maintained libraries/frameworks such as Aeson, Squeleto, Yesod, and Parsec, to name a few, it’s unlikely you will face troubles at all, you just need to be more mindful of what you add as a dependency. There’s stackage.org now, a repository that works with Stack, providing a set of packages that are proven to work well together and help us to have reproducible builds in a more manageable way—not the solution for all the cases but it’s good to have it as an option.

However, we can use Esqueleto (”a bare bones, type-safe EDSL for SQL queries”) with Persistent's serialization to write type-safe SQL queries. It’s unlikely that you want to use Persistent by itself with SQL, so let’s use and review them together.

Postgresql-simple is a great library, it makes a nice use of overloaded strings to do the job. Some other nice libraries to keep an eye on are opaleye (postgres specific, which is equally nice but could be a bit difficult to get why the types are so big) and a combination of persistent (not DB specific! can work on postgres, sqlite, but also noSQL DBs like mongo, it's still easy to learn but you lose some things, such as joins due to the power of being agnostic) + esqueleto for type safe joins (be sure to look up the experimental package, it's a more comfortable syntax that will soon become the default one).

Using esqueleto in one of my haskell projects was a huge time sink and a major barrier to entry for colleagues.

In Haskell: https://hackage.haskell.org/package/esqueleto

Either it analyzes the given SQL to determine the in/out types of each SQL query, or it calls the database describe feature at compile-time.

Writing Haskell programs that rely on third-party packages is still an issue when it’s a not actively maintained package. They get out of date with the base library (Haskell’s standard library), and you might see yourself in a situation where you need to downgrade to an older version. This is not exclusive to Haskell, but it happens more often than I’d like to assume. However, if you only rely on known well-maintained libraries/frameworks such as Aeson, Squeleto, Yesod, and Parsec, to name a few, it’s unlikely you will face troubles at all, you just need to be more mindful of what you add as a dependency. There’s stackage.org now, a repository that works with Stack, providing a set of packages that are proven to work well together and help us to have reproducible builds in a more manageable way—not the solution for all the cases but it’s good to have it as an option.

The Parsec library for Haskell uses combinators, and there are a few good resources around the internet which explore it, if you know Haskell.

Parse the expression using parsec library ( if you're unfamiliar with it please check out https://hackage.haskell.org/package/parsec) it's a strong library for parer combinators. Once you parse the expression u need to define and sum up the similar terms. Check this example out - https://fpunfold.com/2020/05/18/making-a-calculator-in-haskell-with-parsec.html

Konbini is a functional parser combinator library inspired by Haskell parsing libraries like Parsec. It's (hopefully) fairly easy to use, and is about as performant as the better-parse library. In fact, it's quite similar to better-parse in many aspects. The main difference is in how parsers are composed. Where better-parse prefers operators and infix functions, Konbini instead uses plain functions.

Hi everyone, I'm learning F# and currently trying to do a Parsec-like CE, just to get comfortable with computation expressions.

good libraries for parsing: parsec, attoparsec etc.

Thank you! When I read the title I only knew about https://hackage.haskell.org/package/parsec, and for a moment I was very confused…

The more "idiomatic" way would be to use a parser library, e.g. parsec, attoparsec, or megaparsec. But even then I think it would be a lot easier to maintain if you could preserve the angle brackets <> in the input.