scopeName: source.reid
patterns:
  - include: "#expression"
repository:
  expression:
    patterns:
      - include: "#letter"
      - include: "#paren-expression"
  letter:
    match: "a|b|c"
    name: "keyword.letter"
  paren-expression:
    begin: "\\("
    end: "\\)"
    beginCaptures:
      0:
        name: "punctuation.paren.open"
    endCaptures:
      0:
        name: "punctuation.paren.close"
    name: "expression.group"
    patterns:
      - include: "#expression"