Parsing a reserved word in Parsing Expressive Grammar (PEG.js)

Question

The similar question and the author's website give me solutions like this:

Identifier "identifier"
  = !ReservedWord [A-Za-z_]+

ReservedWord
  = "test"
  / "abc"

This solution can't parse an identifier like this "test_var".

In this example, the grammar !ReservedWord will exclusive all variables starting with "test" or "abc".

Thanks in advance.

Answer 1

ReservedWord succeeds, when a reserved word is complete, regardless of what follows. So the solution is to make it fail when there is a longer match that includes more identifier characters:

Identifier "identifier"
  = !ReservedWord [A-Za-z_]+

ReservedWord
  = ( "test" / "abc" ) ![A-Za-z_]