esqueleto VS ghc

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 They get out of date with the base library (Haskell’s standard library), and you might see yourself in a situation where you need to downgrade to an older version.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.

of course it does! what else would you call something like chicken scheme [https://call-cc.org/], ats [https://ats-lang.sourceforge.net/], or ghc [https://www.haskell.org/ghc/]? they are not "scripts", they are full-blown compilers that happen to use C as their compilation target, and then leverage C compilers to generate code for a variety of architecures. it's a very sensible way to do things.

Agree about Haskell... as far as I'm aware there is actually no declarative/easily-readable definition of the Haskell syntax that is also complete, especially when it comes to the indentation rules, and the syntax is basically defined by the very (ironically) imperatively-defined GHC parser[0].

I prefer a syntax like in Pure[1], where the ambiguous, hard to parse indentation-based syntax is replaced by explicit semicolons (Yeah, you can use braces/semicolons in Haskell as well, but most code doesn't).

[0] https://github.com/ghc/ghc/blob/master/compiler/GHC/Parser/L...

[1] https://agraef.github.io/pure-lang/

GHC, the main Haskell compiler

GHCi, version 9.6.3: https://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /Users/daniel/.ghci ghci> :{ | split :: Float -> [Int] | split value = map(read . (:[])) . show | :} :3:15: error: [GHC-83865] • Couldn't match expected type: [Int] with actual type: a0 -> [b0] • Probable cause: ‘(.)’ is applied to too few arguments In the expression: map (read . (: [])) . show In an equation for ‘split’: split value = map (read . (: [])) . show

GHC is hosted on Gitlab, the Github repo is just a mirror. So money.

https://github.com/ghc/ghc

☁ ~ ghci GHCi, version 9.4.7: https://www.haskell.org/ghc/ :? for help ghci> 6 + 3^2 * 4 42

Depending on who you ask, a programming language can be different things. If you ask the Haskell community, many will tell you that the language is the Haskell specification, and that what currently is being used is not Haskell itself, but an extension of Haskell that is supported by the GHC compiler. Similar to the C language, a programming language would be a specification.

GHCi, version 9.4.2: https://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from ~/.dotfiles/ghc/.ghc/ghci.conf