Haskell beginner's playground

This is a Playground for various functionality imlemented in Haskell (and maybe other functional languages like Elm)

Authentication, REST servers, websockets, Web SPA/PWA clients, Postgres, Mongo (with oplog tailing)

Pre-requistes

If you don't have these already, install:

• Stack:
  curl -sSL https://get.haskellstack.org/ | sh
• Elm:
• create-elm-app:
  npm install create-elm-app -g
• PosgreSQL

Preliminary steps

• mv config_sample.dhall config.dhall
• Edit config.dhall and make appropriate changes
• opaleye-gen -d postgresql://localhost/tennis -o src/DB/Opaleye/Database.hs # Uses modifed opaleye-gen

Building

stack build
cd elm-client
elm-app build

Haskell Servant + OIDC.Client Google Auth , Elm client

1. client -> app server
2. server redirects to Google and specifies a callback url
3. Google handles authentication and redirects client to callback url
4. Server gets the user details, creates a JWT and returns HTML+JS to the client sticking the token into localStorage. Also sets window.location to the Elm app's index.html
5. Elm app has JS in index.html to initialize the Elm model from localStorage

Guid to current code 02/17/2020

Elm Client

in directory elm-client, bootstrapped with create-elm-app. Therefore it is a PWA

elm-app build creates a production build in the build directory.

the elm code is in src/Main.elm. The toplevel Javascript code is in src/index.js

The JS code initializes the model from localStorage. it gets authenticated email address and an access-token

TODO

Tech stack

• Authentication: OpenId Connect Google/Microsoft
• Communication : REST + Websockets
• FRP: streamly seems to be a new lib (Claims to be close to Rx in design)
• Client options:
  • Purescript + Halogen + REST+Websocket + Nice default styling
  • [x?] Elm
  • GHCJS Reflex-DOM
  • GHCJS Miso (Not FRP)
  • ReScript
• Servant + Selda + Websocket server + Postgres
• MonadMetrics for metrics

• Streamly for FRP

  Actively maintained, Fastest streaming library, general purpose

• Effect systems

  • Examples of effect systems for same program
  • Polysemy was written by Sandy McGuire, author of "Thinking with Types" and "Algebra Driven Design". Polysemy poor in benchmark that Sandy accepted
  • Tutorial

• Other effect systems

  Effects are things like IO, random numbers, exceptions, mutable global state
  • mtl Basic, Super fast, O(n^2) instances, can't have more than one State, Reader etc.
  • freer-simple Slow, no boilerplate, good type error messages
  • fused effects Super fast, lot of boilerplate
  • Eff By Alexis King, author of freer-simple and that video on Effect systems performance. This is very new, requires GHC changes to boost performance. The changes are not yet accepted
  • Polysemy Very fast, little boilerplate, good error messages

Other useful libraries

Artyom's Haskell toolbox Lists the author's favorite libraries for various tasks

Guided tours of Source code to learn from

• Xmonad
• Realworld Purescript/Halogen
• Elm Realworld Conduit client

Concepts to learn better

• Type level programming. Read Mcguire book
• McGuire also has a book Algebra Driven Design
• Effect systems
• FRP (use streamly?)

References

References