Parse EBNF/Tests

The flavor of EBNF used here is the same as that defined here, except a literal can't contain the character used for quoting, and an identifier can't contain whitespace or any of the characters = | ( ) { } [ ] . ; " '.

A one-liner

<lang ebnf>"a" {

   a = "a1" ( "a2" | "a3" ) { "a4" } [ "a5" ] "a6" ;

} "z"</lang>

Some valid inputs:

a1a3a4a4a5a6
a1 a2a6
a1 a3 a4 a6

Some invalid inputs:

a1 a4 a5 a6
a1 a2 a4 a5 a5 a6
a1 a2 a4 a5 a6 a7
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Arithmetic expressions

<lang ebnf>{

   expr = term { plus term } .
   term = factor { times factor } .
   factor = number | '(' expr ')' .

   plus = "+" | "-" .
   times = "*" | "/" .

   number = digit { digit } .
   digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" .

}</lang>

Some valid inputs:

2
2*3 + 4/23 - 7
(3 + 4) * 6-2+(4*(4))

Some invalid inputs:

-2
3 +
(4 + 3

Some invalid EBNF

<lang ebnf>{ hello world = "1"; }</lang>