Wrote doc for check_input.

doc/extending/ctype.txt

@@ -50,7 +50,7 @@ the most important ones:
 
 .. class:: CLinkerType
 
-    .. method:: c_declare(name, sub)
+    .. method:: c_declare(name, sub, check_input=True)
 
         This must return C code which declares variables. These variables
         will be available to operations defined in C. You may also write
@@ -61,7 +61,7 @@ the most important ones:
         This must return C code which initializes the variables declared in
         ``c_declare``. Either this or ``c_extract`` will be called.
 
-    .. method:: c_extract(name, sub)
+    .. method:: c_extract(name, sub, check_input=True)
 
         This must return C code which takes a reference to a Python object
         and initializes the variables declared in ``c_declare`` to match the
@@ -129,6 +129,11 @@ associated to the Variable is ``py_<name>``.
 ``sub``, on the other hand, is a dictionary containing bits of C code
 suitable for use in certain situations. For instance, ``sub['fail']``
 contains code that should be inserted wherever an error is identified.
+
+``c_declare`` and ``c_extract`` also takes a third ``check_input`` 
+optional argument. If you want your type to validate its inputs, it must
+do it only when ``check_input`` is True.
+
 The example code below should help you understand how everything plays
 out:
 

doc/tutorial/extending_theano.txt

@@ -92,6 +92,8 @@ Op Contract
         def flops(self, inputs, outputs):
             pass
         
+        check_input = True
+
 .. ../extending/op.txt
 
 There are two mandatory methods that one needs to implement.
@@ -133,6 +135,10 @@ string representation of your op.
 The :func:`R_op` method is needed if you want ``theano.tensor.Rop`` to
 work with your op.
 
+The optionnal boolean :func:'check_input' attribute is used to specify if you want the types used in 
+your op to check their inputs in their c_code. It can be used to speed up compilation and reduce the 
+number of generated c_file.
+
 Op Example
 ==========