anchor.diff:                  label Javascript
   
               #output.fill-container.container
  -                // ko if: errors()
  -                pre#error.scroll-box(data-bind="text: errors")
  -                // /ko
  -                // ko if: view() == 'js' && !errors()
  +                // ko if: view() == 'js'
  +                // ko ifnot: compilerErrors
                   code#compiledCode.scroll-box
                       pre(data-bind="text: compiledJs")
                   // /ko
  -                // ko if: view() == 'ast' && !errors()
  +                // ko if: compilerErrors
  +                pre#error.scroll-box(data-bind="text: compilerErrors")
  +                // /ko
  +                // /ko
  +                // ko if: view() == 'ast'
  +                // ko ifnot: parserErrors
                   code#compiledCode.scroll-box
                       pre(data-bind="text: JSON.stringify(ast(), null, '    ')")
                   // /ko
  +                // ko if: parserErrors
  +                pre#error.scroll-box(data-bind="text: parserErrors")
  +                // /ko
  +                // /ko
  
positive.code:                         try {
                              this.ast(angl.parse(this.inputAngl()))
                          } catch(e) {
                              this.errors(e.message)
                              return
                          }
                          try {
                              this.compiledJs(compiler(this.ast()))
                          } catch(e) {
                              this.errors(e.message)
                              return
                          }
                          this.errors(undefined)
                      }, this).extend({throttle: 500})
                  }).apply(viewModel)
  
  
negative.code:                 var viewModel = window.viewModel = {}
                  ;(function() {
                      this.view = ko.observable('js')
                      this.parserErrors = ko.observable()
                      this.compilerErrors = ko.observable()
                      this.ast = ko.observable()
                      this.compiledJs = ko.observable()
                      this.inputAngl = ko.observable('')
  