gistfile1.txt

grammar dreme::datum::Grammar {

token TOP {
    <datum>
    [ $ || <.panic: "Syntax error"> ]
}

## Lexer items

# This <ws> rule treats # as "comment to eol".
token ws {
    <!ww>
	<comment>*
}

token comment {
	| <line_comment>
	| <nested_comment>
}

token line_comment {
	';' \N* \n?
}

token nested_comment {
	'#|' ~ '|#' .
}

## Data

rule datum {
	| <simple_datum>
    | <compound_datum>
}

rule simple_datum {
    | <boolean>
	| <character>
	| <number>
	| <string>
	| <symbol>
	| <bytevector>
}

rule compound_datum {
	| <list>
	| <vector>
}

rule symbol { <identifier> }

rule list {
	| '(' ~ ')' <list_data>
	| '[' ~ ']' <list_data> # R6RS
}

rule list_data {
	| <datum>*
	| <datum>+ '.' <datum>
	| <datum> '.' <datum> '.' <datum> # Racket
}

rule abbreviation {
	| "'" <datum>
	| '`' <datum>
	| ',' <datum>
	| ',@' <datum>
}

rule vector {
	'#' '(' ~ ')' <datum>*
}

token bytevector_hash {
	| '#vu8' # R6RS
	| '#u8'  # R7RS
}

rule bytevector {
	<bytevector_hash> '(' ~ ')' <u8>
}

token u8 {
	\d**1..3 <?{$/ < 256}>
}
}

say dreme::datum::Grammar.parse('228');