Trying to get a minimal example of GLSL in PureScript

HelloGlsl.purs

module Example.HelloGlsl where

import Prelude (Unit(..)
               ,($)
               ,bind)

import Control.Monad.Eff (Eff(..))
import Control.Monad.Eff.Alert (Alert(..)
                               ,alert)
import Control.Monad.Eff.Console (CONSOLE(..)
                                 ,log)
import Data.Matrix4 (Mat4(..))
import Data.Vector3 (Vec3(..))
import Graphics.WebGL (Attribute(..)
                      ,Capacity(..)
                      ,Mask(..)
                      ,Shaders(..)
                      ,Uniform(..)
                      ,clear
                      ,clearColor
                      ,enable
                      ,getCanvasHeight
                      ,getCanvasWidth
                      ,runWebGL
                      ,viewport
                      ,withShaders)

type Bindings = (aVertexPosition :: Attribute Vec3
                ,uPMatrix :: Uniform Mat4
                ,uMVMatrix:: Uniform Mat4)

shaders :: Shaders (Object Bindings)
shaders = Shaders
  """
  precision mediump float;

  void main(void) {
    gl_FragColor = vec4(1.0, 0.0, 1.0, 1.0);
  }
  """
  """
  attribute vec3 aVertexPosition;

  uniform mat4 uMVMatrix;
  uniform mat4 uPMatrix;

  void main(void) {
      gl_Position = uPMatrix * uMVMatrix * vec4(aVertexPosition, 1.0);
  }
  """

main :: Eff (console :: CONSOLE, alert :: Alert) Unit
main = do
  runWebGL "hello-glsl" (\s -> alert s)
    \context -> do
      log "WebGL started..."
      withShaders shaders (\s -> alert s)
        \bindings -> do
          log "Shaders and bindings ready..."
          clearColor 0.0 0.0 0.0 1.0
          enable DEPTH_TEST

          canvasWidth <- getCanvasWidth context
          canvasHeight <- getCanvasHeight context
          viewport 0 0 canvasWidth canvasHeight
          clear [COLOR_BUFFER_BIT, DEPTH_BUFFER_BIT]
          log "WebGL completed"