Simplify abstract syntax further. Added OML exporter and test.

shell.nix

@@ -0,0 +1,15 @@
+# Generates a shell from where all the dependencies can be found.
+
+{ pkgs ? import <nixpkgs> {} }:
+
+let
+  SOURCE_DIR = builtins.toString ./src;
+in
+  pkgs.mkShell {
+    buildInputs = [
+      pkgs.python3
+      pkgs.python3Packages.jinja2
+    ];
+
+     PYTHONPATH = SOURCE_DIR;
+  }