code: func (v *evalVisitor) blockParam(name string) interface{} {
  	for i := len(v.blockParams) - 1; i >= 0; i-- {
  		for k, v := range v.blockParams[i] {
  			if name == k {
  				return v
  			}
  		}
  	}
  
  	return nil
  }
docs: // blockParam iterates on stack to find given block parameter, and returns its value or nil if not founc