Check the Cython version

Check the Cython version when installing. At least Cython version 0.23
is required.

CMakeLists.txt

@@ -161,6 +161,9 @@ message("-- Eigen dir is " ${EIGEN3_INCLUDE_DIR})
 find_package(Eigen3 REQUIRED)
 include_directories(${EIGEN3_INCLUDE_DIR})
 
+# look for Cython
+find_package(Cython REQUIRED)
+
 FIND_PACKAGE(Threads REQUIRED)
 set(LIBS ${LIBS} ${CMAKE_THREAD_LIBS_INIT})
 

cmake/FindCython.cmake

@@ -0,0 +1,58 @@
+# Find the Cython compiler.
+#
+# This code sets the following variables:
+#
+#  CYTHON_EXECUTABLE
+#
+
+#=============================================================================
+# Copyright 2011 Kitware, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#=============================================================================
+
+# Set minimal accepted version
+set(CYTHON_REQUIRED_VERSION 0.22)
+
+# Use the Cython executable that lives next to the Python executable
+# if it is a local installation.
+find_package( PythonInterp )
+if( PYTHONINTERP_FOUND )
+  get_filename_component( _python_path ${PYTHON_EXECUTABLE} PATH )
+  find_program( CYTHON_EXECUTABLE
+    NAMES cython cython.bat cython3
+    HINTS ${_python_path}
+    )
+else()
+  find_program( CYTHON_EXECUTABLE
+    NAMES cython cython.bat cython3
+    )
+endif()
+
+# Check version
+if(CYTHON_EXECUTABLE)
+  execute_process(COMMAND ${CYTHON_EXECUTABLE} -V
+    ERROR_VARIABLE CYTHON_OUTPUT OUTPUT_QUIET)
+  string(REGEX REPLACE "^Cython version ([0-9]+\\.[0-9]+).*" "\\1" CYTHON_VERSION "${CYTHON_OUTPUT}")
+
+  if(${CYTHON_VERSION} VERSION_LESS ${CYTHON_REQUIRED_VERSION})
+    message(FATAL_ERROR "DyNet needs at least Cython version ${CYTHON_REQUIRED_VERSION}, found verson ${CYTHON_VERSION}")
+  else()
+    message(STATUS "Found Cython version ${CYTHON_VERSION}")
+  endif()
+endif()
+
+include( FindPackageHandleStandardArgs )
+FIND_PACKAGE_HANDLE_STANDARD_ARGS( Cython REQUIRED_VARS CYTHON_EXECUTABLE )
+
+mark_as_advanced( CYTHON_EXECUTABLE )