Haskell Servant with Persistent and Postgres

Setup notes

Run postgres in docker

docker compose up -d

Build and Run program in docker container to avoid issues on a Windows machine.

docker build -t haskell-postgres .
docker compose -f docker-compose-dev.yml up -d
docker exec -it haskel-dev bash
stack build
stack exec haskel-servant-rest-api-exe

stack build && stack exec haskel-servant-rest-api-exe

Haskel Notes

Funktor Applicative Monad

Functor is a type class that defines a mapping function over a type constructor. It allows you to apply a function to the value inside a context (like Maybe, List, etc.). Applicative is a type class that extends Functor. It allows you to apply functions that are also in a context to values in a context. It provides the ability to lift functions into the context. Monad is a type class that extends Applicative. It allows for chaining operations together, where the output of one operation can be used as the input to the next. It provides a way to handle computations that involve side effects or context.

Visual Metaphor Imagine context as a box:

🟦 Functor: You can apply a function inside the box, but not change the box.

🟪 Applicative: You can apply a function in a box to a value in a another box (multiple boxes working together).

🟥 Monad: You can look inside the box, do something, and return a new box (the next step can depend on the previous).