+# The various FIELDS are:
+#
+# - has_id: 0 or 1.
+# Whether the symbol has an id.
+# - id: string
+# If has_id, the id. Guaranteed to be usable as a C identifier.
+# - tag: string.
+# A representat of the symbol. Can be 'foo', 'foo.id', '"foo"' etc.
+# - user_number: integer
+# The assigned (external) number as used by yylex.
+# - is_token: 0 or 1
+# Whether this is a terminal symbol.
+# - number: integer
+# The internalized number (used after yytranslate).
+# - has_type: 0, 1
+# Whether has a semantic value.
+# - type
+# If it has a semantic value, its type tag, or, if variant are used,
+# its type.
+# - has_printer: 0, 1
+# - printer: string
+# - printer_file: string
+# - printer_line: integer
+# If the symbol has a printer, everything about it.
+# - has_destructor, destructor, destructor_file, destructor_line
+# Likewise.
+#