Let's talk about PureScript

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an exciting trip through history prelude

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1936 Lambda Calculus is born

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1990 A bunch of smart people start working Haskell

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1995 Brendan Eich is hired by NetScape to write Scheme for the browser

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Spoiler alert: He doesn't write a Scheme for NetScape

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2016

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You shouldn't be sad.

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Maybe those functional dudes got something right.

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let's talk about purescript Kārlis Lauva @skazhy frontend rīga meetup, 2016

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Hello. I write Clojure and dabble with other things This is not a monad tutorial This is, like, my opinion

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So, Haskell for the browser, eh

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module Main where import Prelude import Control.Monad.Eff import Control.Monad.Eff.Console sup :: String -> String sup g = "sup, " ++ g main :: forall e. Eff (console :: CONSOLE | e) Unit main = do log $ sup "world"

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turns out, functional programming languages are really useful for web things

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but javascript too can be purely functional

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let's discuss the bad parts

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[Object object]

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an *actual* type system

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purescript makes this example boring

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like, really boring

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sketchy branching

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pattern matching

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data Behavior = KillHumans | BeNiceToHumans type Robot = { naughty :: Boolean } interactWithHumans :: Robot -> Behavior interactWithHumans { naughty: true } = KillHumans interactWithHumans { naughty: false } = BeNiceToHumans

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data Behavior = KillAllHumans | BeNiceToHumans | KillOnlyVapers type Robot = { niceness :: Int } interactWithHumans :: Robot -> Behavior interactWithHumans { niceness: 0 } = KillAllHumans interactWithHumans { niceness: 1 } = KillOnlyVapers interactWithHumans _ = BeNiceToHumans

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callback hell

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monads

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fetchRobots(function(response) { assembleFleet(function(robots) { if (robots) return robots; }, function(error { .. }); }, function(error) {... });

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data RobotArmy = Army (List Robot) fetchRobots = do robotParts <- get "/robotParts" robots <- assembleFleet robotParts return $ Army robots

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does purescript survive in the real world?

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yes.

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ecosystem and tooling

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psc short for "purescript compiler"

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modules managed via bower

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• build tool => pulp • hoogle for purescript => pursuit

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purescript - javascript teamwork

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back to killer robots

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data Behavior = KillHumans | BeNiceToHumans instance showBehavior :: Show Behavior where show KillHumans = "kill all humans11" show BeNiceToHumans = "humans, you are pretty tite" type Robot = { naughty :: Boolean } interactWithHumans :: Robot -> Behavior interactWithHumans { naughty: true } = KillHumans interactWithHumans { naughty: false } = BeNiceToHumans safeInteract :: Boolean -> String safeInteract x = show $ interactWithHumans { crazyMurderer : x }