compile () {
      const expr = this._compile(mathWithTransform, {})
      const args = {}
      const context = null

      function evaluate (scope) {
        const s = createMap(scope)
        _validateScope(s)
        return expr(s, args, context)
      }

      return {
        evaluate
      }
    }
Compile the node into an optimized, evauatable JavaScript function
@return {{evaluate: function([Object])}} object
               Returns an object with a function 'evaluate',
               which can be invoked as expr.evaluate([scope: Object]),
               where scope is an optional object with
               variables.