-s ::= ws grammar ws => "gram"
-ws !::= w**
-grammar ::= r +/ ws => "grammar"
-r ::= word ^"::=" alternatives /ws
- | word ^"!::=" alternatives /ws
-
-alternatives ::= (conjuncts +/ (ws "|" ws)) +/ (ws ">" ws)
-
-conjuncts ::= sequence
- | sequence ^"&" e*/ws /ws
- | sequence ^"&~" e*/ws /ws
-
-ps ::= e*/ws => "ps"
- | (e+/ws ws)? "^" quoted (ws e+/ws)? => "ps2"
-psx ::= ps
- > ps ^"/" e /ws
-sequence ::= psx
- | psx ^"=>" (word|quoted) /ws
-
-ec ::= [~\-\]\\\~]
- | escaped
-
-range ::= ec => "range"
- | ec ^"-" ec
-
-e ::= word => "nonTerminal"
- | quoted => "literal"
- | ^"()"
- | ^"{" sequence "}" /ws
- | ^"[" range* "]"
- | ^"[~" range* "]"
-
- | (e ws ^"**" > e ws ^"*")
- | e ^"*/" e /ws
- | (e ws ^"++" > e ws ^"+")
- | e ^"+/" e /ws
- | e ^"?" /ws
-
- | "(" word ^")" /ws
- > ^"(" alternatives ")" /ws
-
-w !::= " "
- | "//" ([~\n]*) "\n"
- | "\n"
- | "\r"
-word ::= [a-zA-Z0-9_]++
-quoted ::= "\"" (([~\"\\] | escaped)+) "\""
- | "\"\"" => ""
-escaped ::= "\\n" => "\n"
- | "\\r" => "\r"
- | "\\" [~nr]