Another Python example

Again, from the reference manual:

dict_display ::= "{" [ key_datum_list ] "}"
key_datum_list ::= key_datum ( "," key_datum )* [","]
key_datum ::= expression ":" expression

In PGE, this becomes:

rule dict_display   { <'{'> <key_datum_list>? <'}'> }

rule key_datum_list { <key_datum> [ , <key_datum> ]* ,? }

rule key_datum      { <expression> <':'> <expression> }