PureScript: Pattern matching and @ syntax

Main.purs

module Main where

import Prelude

import Data.Maybe (Maybe(..))
import Effect (Effect)
import Effect.Console (log)

data Dish = Dish Pasta (Maybe Sauce)

dishToString :: Dish -> String
dishToString _ = "I’m a dish"

data Sauce
  = Marinara { spicy :: Boolean }
  | Carbonara
  | Pesto

sauceToString :: Sauce -> String
sauceToString (Marinara { spicy }) = "marinara (spicy: " <> show spicy <> ")"
sauceToString Carbonara = "carbonara"
sauceToString Pesto = "pesto"

instance Show Sauce where
  show = sauceToString

data Pasta
  = Spaghetti
  | Linguine
  | Macaroni

pastaToString :: Pasta -> String
pastaToString Spaghetti = "spaghetti"
pastaToString Linguine = "linguine"
pastaToString Macaroni = "macaroni"

main :: Effect Unit
main = do
  let
    -- dish1 = Dish Linguine (Just Carbonara)
    -- dish2 = Dish Macaroni (Just (Marinara { spicy: true }))
    dish3 = Dish Macaroni (Just (Marinara { spicy: false }))

  case dish3 of
    Dish pasta Nothing -> do
      log ("Pasta " <> pastaToString pasta <> " without sauce")
    Dish _ (Just (Marinara { spicy })) | spicy -> do
      -- log ("Spicy marinara: " <> show (Just (Marinara { spicy: true })))
      log ("Spicy marinara: " <> show spicy)
    Dish pasta outerSauce@(Just sauce) -> do
      log ("Pasta " <> pastaToString pasta <> " with " <> sauceToString sauce <> " sauce")
      log ("Sauce: " <> show outerSauce)
      -- log ("Sauce: " <> show (Just sauceToString sauce))


isSpicy :: Sauce -> Boolean
isSpicy (Marinara { spicy }) = spicy
isSpicy Pesto = false
isSpicy Carbonara = false