JSON Schema Compiler supports functions as PropertyTypes.

tools/json_schema_compiler/cpp_util.py

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 """Utilies and constants specific to Chromium C++ code.
 """
 
 from datetime import datetime
 from model import PropertyType
 import os
 
@@ skipping 37 matching lines @@
 def GetValueType(type_):
   """Returns the Value::Type corresponding to the model.PropertyType.
   """
   return {
       PropertyType.STRING: 'Value::TYPE_STRING',
       PropertyType.INTEGER: 'Value::TYPE_INTEGER',
       PropertyType.BOOLEAN: 'Value::TYPE_BOOLEAN',
       PropertyType.DOUBLE: 'Value::TYPE_DOUBLE',
       PropertyType.ENUM: 'Value::TYPE_STRING',
       PropertyType.OBJECT: 'Value::TYPE_DICTIONARY',
+      PropertyType.FUNCTION: 'Value::TYPE_DICTIONARY',
       PropertyType.ARRAY: 'Value::TYPE_LIST',
       PropertyType.BINARY: 'Value::TYPE_BINARY',
   }[type_]
 
 def GetParameterDeclaration(param, type_):
   """Gets a parameter declaration of a given model.Property and its C++
   type.
   """
   if param.type_ in (PropertyType.REF, PropertyType.OBJECT, PropertyType.ARRAY,
       PropertyType.STRING):
     arg = '%(type)s& %(name)s'
   else:
     arg = '%(type)s %(name)s'
   return arg % {
     'type': type_,
     'name': param.unix_name,
   }
 
 def GenerateIfndefName(path, filename):
     """Formats a path and filename as a #define name.
 
     e.g chrome/extensions/gen, file.h becomes CHROME_EXTENSIONS_GEN_FILE_H__.
     """
     return (('%s_%s_H__' % (path, filename))
             .upper().replace(os.sep, '_').replace('/', '_'))