docs and gm pretty printer

docs/src/commentary/gm.rst

@@ -207,3 +207,30 @@ WIP. state transition rules
    & m
    }
 
+*********************************
+Compilation: How to Squash a Tree
+*********************************
+
+WIP.
+
+Notice that we do not keep a (local) environment at run-time. The environment
+only exists at compile-time to map local names to stack indices. When compiling
+a supercombinator, the arguments are enumerated from zero (the top of the
+stack), and passed to :code:`compileR` as an environment.
+
+.. literalinclude:: /../../src/GM.hs
+   :dedent:
+   :start-after: -- >> [ref/compileSc]
+   :end-before: -- << [ref/compileSc]
+   :caption: src/GM.hs
+
+Of course, variables being indexed relative to the top of the stack means that
+they will become inaccurate the moment we push or pop the stack a single time.
+The way around this is quite simple: simply offset the stack when w
+
+.. literalinclude:: /../../src/GM.hs
+   :dedent:
+   :start-after: -- >> [ref/compileC]
+   :end-before: -- << [ref/compileC]
+   :caption: src/GM.hs
+