Merge pull request #753 from goodfeli/doc_gof

theano/gof/__init__.py

+"""
+gof.py
+
+gof stands for Graph Optimization Framework
+
+The gof submodule of theano implements a framework
+for manipulating programs described as graphs. The
+gof module defines basic theano graph concepts:
+    -Apply nodes, which represent the application
+of an Op to Variables. Together these make up a
+graph.
+    -The Type, needed for Variables to make sense
+    -The FunctionGraph, which defines how a subgraph
+should be interpreted to implement a function
+    -The Thunk, a callable object that becames part
+of the executable emitted by theano
+    -Linkers/VMs, the objects that call Thunks in
+sequence in order to execute a theano program
+
+Conceptually, gof is intended to be sufficiently abstract
+that it could be used to implement a language other than
+theano. ie, theano is a domain-specific language for
+numerical computation, created by implementing
+tensor Variables and Ops that perform mathematical functions.
+A different kind of domain-specific language could be
+made by using gof with different Variables and Ops.
+In practice, gof and the rest of theano are somewhat more
+tightly intertwined.
+
+Currently, gof also contains much of the C compilation
+functionality. Ideally this should be refactored into
+a different submodule.
+
+For more details and discussion, see the theano-dev
+e-mail thread "What is gof?"
+"""
+
 import sys
 
 from cc import \