@@ No support for template ids
@@ No support for expressions (e.g., 2*2)

Token types:
      keyword
      identifier      
      punctuation (";" "{" "}" "(" ")" "," "|" "=" ":")
      bracket-literal
      string-literal     
      bool-literal
      int-literal
      float-literal
      end-of-stream

def-unit:
	include-decl-seq(opt) decl-seq(opt)

include-decl-seq:
	include-decl
	include-decl-seq include-decl;

include-decl:
	"include" path-literal ";"

decl-seq:
	decl
	decl-seq decl

decl:
	namespace-def
	class-def

namespace-def:
	"namespace" identifier "{" namespace-body "}"

namespace-body:
	decl-seq(opt)

class-def:
	"class" identifier "{" option-def-seq(opt) "};"

option-def-seq:
	option-def
	option-def-seq option-def

option-def:
	type-spec option-name-seq initializer(opt) ";"

type-spec:
	fundamental-type-spec
	qualified-name

option-name-seq:
	option-name
	option-name-seq "|" option-name;

option-name:
	option-identifier
	string-literal

initializer:
	"=" argument-expr
	"(" argument-seq(opt) ")"

argument-seq:
	argument-expr
	argument-seq "," argument-expr

argument-expr:
	bool-literal
	int-literal
	float-literal
	string-literal
	qualified-name

qualified-name:
	identifier
	qualified-name "::" identifier

fundamental-type-spec:
	"bool"
	 ...
	"long double"