ramirez7

I often see effects called "fancy," but in 2024 I fail to see how that is the case. If anything, their types are more clear than mtl in 2024.

I've been using extensible effects (via cleff [1]) in my gamedev code since 2021 (starting with Ludum Dare 49). I originally used mtl, but it was almost immediately a pain. I saw cleff and switched to it within a day (for both library code + my previous game). I can confidently say I'll never use mtl again if I have any choice. It's archaic and brings no benefit besides somehow being considered less fancy.

I say "somehow" because I don't really understand why mtl is considered less fancy than cleff. Maybe it's because it's fancier to implement? But the whole point of Haskell is that you shouldn't need to care about the implementation if

ramirez7

{-# LANGUAGE AllowAmbiguousTypes #-}

import Data.Coerce
import Data.Foldable

foldMapVia
  :: forall b f r a
   . Coercible r b
  => Monoid b
  => Foldable f

ramirez7

-- Similar to this old gist https://gist.github.com/ramirez7/11167d5f1c2a1153c3fb20643f4cb2d4
--
-- Scala is a bit more general though thanks to its path-dependent types
module SetBy
  ( SetBy
  ) where

import Data.Map (Map)
import qualified Data.Map as Map
import GHC.TypeLits

ramirez7

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE UndecidableInstances #-}
{-# OPTIONS_GHC -freduction-depth-0 #-}

import GHC.TypeLits

data N = Z | S N

ramirez7

:{
let ghciTime cmd = do
     let mkVar n u = "ghciTime_" ++ n ++ "_" ++ show (Data.Unique.hashUnique u)
     startVar <- mkVar "start" <$> Data.Unique.newUnique
     resVar <- mkVar "res" <$> Data.Unique.newUnique
     endVar <- mkVar "end" <$> Data.Unique.newUnique
     pure $ unlines
       [ startVar ++ " <- Data.Time.getCurrentTime"
       , resVar ++ "<- " ++ cmd
       , endVar ++ " <- Data.Time.getCurrentTime"

ramirez7

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE GADTs #-}

module HList.GADT where

import Data.Kind

data HList (ts :: [Type]) where
  HNil :: HList '[]
  HCons :: forall t ts. t -> HList ts -> HList (t ': ts)

ramirez7

{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE LambdaCase #-}

import Data.Kind

data I a
data X a

data XX

ramirez7

:{
let doTH code = do
      u <- Data.Unique.newUnique
      let decls = "ghciTH_" ++ show (Data.Unique.hashUnique u)
      pure $ unlines
        [ unwords ["let", decls, "=", code]
        , "() = ();" ++ decls
        ]
:}

ramirez7

concat(zipWith replicate [1,2,1,0] "cold")

-- Desugar string literal to [Char]
concat(zipWith replicate [1,2,1,0] ['c', 'o', 'l', 'd'])

-- https://hackage.haskell.org/package/base-4.19.0.0/docs/src/GHC.List.html#zipWith
-- Rewritten to not use the "go" helper, zipWith is:
-- zipWith f [] _ = []
-- zipWith f _ [] = []
-- zipWith f (x:xs) (y:ys) = f x y : zipWith f xs ys

ramirez7