The ReaderT Design Pattern - FP Complete

Often times I’ll receive or read questions online about “design patterns” in Haskell. A common response is that Haskell doesn’t have them. What many languages address via patterns, in Haskell we address via language features (like built-in immutability, lambdas, laziness, etc). However, I believe there is still room for some high-level guidance on structuring programs, which I’ll loosely refer to

[Nnwww]

StateT IOは無意味だからReaderT IOを使おう、状態はMutVar派生で扱おう、テストも考慮して環境となる構造体にlensを使おう、Monad型クラスから拡張することでMonadIOを一部のロジックで外せる

[ilyaletre]

snoymanの話を見る限り、割とstackにはベストプラクティスが導入されているっぽい。

[igrep]

ReaderT env IOで大体いろいろ出来ちゃう。Stateは純粋な関数としてのみ使おう。