Partial solution to third problem in first set of exercises in Chapter 9 of PureScript by Example

Plot.purs

module Plot where

import Prelude (($), bind, return)

import Control.Monad.Eff (Eff(..))
import Data.List (List(..), toList)
import Data.Maybe (Maybe(..))
import Graphics.Canvas ( Canvas(..)
                       , Context2D(..)
                       , closePath
                       , getCanvasElementById
                       , getContext2D
                       , lineTo
                       , moveTo
                       , rect
                       , setFillStyle
                       , setStrokeStyle
                       , strokePath)

type Point =
  { x :: Number
  , y :: Number
  }

renderPath :: forall eff. Context2D ->
                          Array Point ->
                          Eff (canvas :: Canvas | eff) Context2D
renderPath ctx pts = renderPath' $ toList pts where
  renderPath' pts' =
    case pts' of
      (Cons { x: x1, y: y1 }
            pts''@(Cons { x: x2, y: y2 } _)) -> do
        strokePath ctx $ do
          moveTo ctx x1 y1
          lineTo ctx x2 y2
        closePath ctx
        renderPath' pts''
      _ -> return ctx

main = do
  Just canvas <- getCanvasElementById "canvas"
  ctx <- getContext2D canvas

  setStrokeStyle "#0000FF" ctx
  renderPath ctx [{ x: 100.0, y: 200.0 }
                 ,{ x: 300.0, y: 300.0 }]