Good Haskell Libraries

Nice list, though for things like semialign I'd probably just write my own function rather than add a dep.

If we're recommending, here are some that I enjoy using:

• typed-process – type-safe shelling out
• postgresql-simple – simple db workhorse
• attoparsec – fast, readable parser combinators
• tagsoup – easy scraping
• async and stm – do stuff concurrently and safely
• stm-containers – necessary when changing maps in stm
• vector-hashtables – much faster than unordered-containers
• fast-logger – simple logging workhorse
• optparse-applicatives – easily, declaratively define cli arg handling
• wai – simple http serving
• alfred-margaret – fast search for multiple strings in big texts
• dataframe – for exploring data (though I have yet to use in production)
• doctest – for inline tests
• QuickCheck – the OG property testing framework. I know people say hedgehog is better, but there are more docs and integrations for QC, so it feels more comfortable

I've used almost none of these! I've had exposure to regex-tdfa (via hledger) and I found it semi-awkward, although that could be the way it's embedded in hledger; I also adopted the mentioned algebraic-graphs which I would generally recommend although for the thing I used it for ultimately I decided I shouldn't have.

I'll throw out a recommendation for HTF (haskell testing framework) which for some reason seems very out-of-favour. It wraps HUnit and QuickCheck, but lets you write tests or properties in one-liners right next to the code they are testing, without any boilerplate. No need to build weird heirarchies of test trees; the test function names are their description. I find that reduced friction is great for encouraging me to actually write tests:

def someFunction :: SomeIn -> SomeOut
someFunction = ...

test_someFunction_fooble = ...
prop_someFunction_fnargh = ...