A Parsing Expression Grammar to Turn Buffalo into Fish

gistfile1.txt

/*
 * Use this at http://pegjs.majda.cz/online
 *
 * Buffalo buffalo Buffalo buffalo buffalo buffalo Buffalo buffalo
 * - becomes -
 * Fishy fish fishy fish fish fish fishy fish
 *
 * Also, the grammar is recursive, so it could also generate ALL THE FISH.
 */

start
  = np:nounphrase " " vp:verbphrase "." { var s = np + " " + vp + "."; return s.charAt(0).toUpperCase() + s.slice(1); }

nounphrase
  = pn:propernoun " " n:noun " " rc:relativeclause { return pn + " " + n + " " + rc; }
  / pn:propernoun " " n:noun { return pn + " " + n; }

verbphrase
  = v:verb " " np:nounphrase { return v + " " + np; }

relativeclause
  = np:nounphrase " " v:verb { return np + " " + v; }

propernoun = "Buffalo" { return "fishy" }
noun = "buffalo" { return "fish"; }
verb = "buffalo" { return "fish"; }

Input: "Buffalo buffalo Buffalo buffalo buffalo buffalo Buffalo buffalo Buffalo buffalo Buffalo buffalo Buffalo buffalo buffalo buffalo buffalo."
Output: "Fishy fish fishy fish fish fish fishy fish fishy fish fishy fish fishy fish fish fish fish."