parser.rkt

#lang brag

;; A parser for R-Expressions

rex                 : implicit-expression [ ":" explicit-expression ]
implicit-expression : [STAR] (limited-expression [STAR])*
explicit-expression : node-line ("," node-line)*

limited-expression  : transition | loop | sub-expression
sub-expression      : "(" ( branch | limited-expression )+ ")"
loop                : "{" ( limited-expression )+ "}"
branch              : "|"

node-line           : ["="] node-identifier (transition "-" ">" node-identifier)*
node-identifier     : (NUMBER | ALPHA | PUNCTUATION)+

transition          : character | range | GLOB | except
range               : "[" span ("," span)* "]"
span                : character ["-" character]
except              : "!" character

;; In addition to the regular ascii escape sequences
;; the following characters are reserved and have to be escaped with \:
;; space;:*.,{}[]|\-=!
character           : NUMBER | ALPHA | PUNCTUATION | ESCAPED-CHAR