Main.hs

{-

State monad things, but in Haskell.

I am but a humble FP noob.

-}

module Main where

import Control.Monad.State

type GameState = (Bool, Int)

-- convenience type
-- a limitations is that when there are multiple value types, these "convenience"
-- types can become numerous and less convenient
type Transform = State GameState GameState

addSeventeen :: Transform
addSeventeen = do
  (on, n) <- get
  return (on, n + 17)

addOne :: Transform
addOne = do
  (on, n) <- get
  return (on, n + 1)

inputToTransform :: Bool -> Transform
inputToTransform x =
  case x of
    True  -> addSeventeen
    False -> addOne

applyTransforms :: [Transform] -> Transform
applyTransforms inputs = do
  initialState <- get
  return $ foldl (\state input -> evalState input state) initialState inputs

-- point-free!
transform :: [Bool] -> Transform
transform = (applyTransforms . map inputToTransform)

main :: IO ()
main = do
  let game = (True, 0)
  let inputs = [True, False, False, False]
  print $ runState (transform inputs) game

similar.cabal

name:                similar
version:             0.1.0.0
-- synopsis:
-- description:
license:             BSD3
license-file:        LICENSE
-- copyright:
-- category:
build-type:          Simple
extra-source-files:  ChangeLog.md
cabal-version:       >=1.10

executable lol-woops
  main-is:             Main.hs
  -- other-modules:
  -- other-extensions:
  build-depends:       base >=4.10 && <4.11, mtl
  hs-source-dirs:      .
  default-language:    Haskell2010