intern-resources/readme.md

thunderstrike.ai intern resources

purescript

Purescript is a strongly-typed ^{[type safety]} purely functional ^{[purely functional]} programming language that compiles to javascript (like typescript).

In brief

• effectful code ^{[side effect]} is isolated from non-effectful code. This makes programs much more consistent to run and reason about.
• everything is an expression
• interacting with raw javascript is relatively painless

Motivating example: React vs Halogen

this frontend app:

1. renders "Loading..." until either data or error
2. fetches data from a server
3. if ok, render items in a list. if error, render error span at the bottom of the page.

React

export const App = () => {
  const [items, setItems] = React.useState(undefined)
  const [error, setError] = React.useState(undefined)

  React.useEffect(() => {
    fetch('/api/item')
      .then(rep => rep.json())
      .then(items => setItems(items))
      .catch(e => setError(e))
  }, [])

  return error !== undefined
    ? (<p class="error">{error.message}</p>)
    : items === undefined
    ? (<p>Loading...</p>)
    : items.map(item => {
        return (
          <div key={item.id}>
            <p>{item.title}</p>
            <span class="small">{item.description}</span>
          </div>
        )
      })
}

Halogen

type Item = {id :: String, title :: String, description :: String}
data State = StateEmpty | StateErrored Error | StateGotItems (Array Item)
data Action = Init

renderItem item = div [] [ p [] [text item.title]
                         , span [className "small"] [text item.description]
                         ]

renderApp StateEmpty = p [] [text "Loading..."]
renderApp (StateErrored e) = p [className "error"] [text (message e)]
renderApp (StateGotItems items) = map renderItem items

action Init = do
  response <- fetch (URL "/api/item") {method: Get}
  jsonString <- text response
  itemsOrError <- readJSON jsonString
  case itemsOrError of
    Right items -> put (StateGotItems items)
    Left error -> put (StateErrored error)

app = mkComponent
  { initialState: StateEmpty
  , render: renderApp
  , eval: mkEval (defaultEval {handleAction = action, initialize: Just Init})
  }