{ "proxy_foo_reader":
  { "vars": ["FOO"]
  , "imports": {"read_foo": "real_foo_reader"}
  , "expression": {"type": "CALL_EXPRESSION", "name": "read_foo"}
  }
, "real_foo_reader":
  {"vars": ["FOO"], "expression": {"type": "var", "name": "FOO"}}
}