!747

m {
  !include #1001196 // Lisp
  
  static new L<Lisp> rules;
  static new L<S> statements;
  
  p {
    rules.add(equ("$1 is the singular of $2.", "$2 is the plural of $1."));
    statements.add("house is the singular of houses.");
    process();
    print(fromLines(statements));
  }
  
  static void process() {
    for (Lisp rule : rules) {
      if (!rule.is("equ")) continue;
      S l = rule.getString(0), r = rule.getString(1);
      for (Map<S, S> m : matchStatements(l)) {
        addStatement(convert(r, m));
      }
    }
  }
  
  static L<Map<S, S>> matchStatements(S pat) {
    L<Map<S, S>> l = new ArrayList<Map<S, S>>();
    for (S s : statements) {
      Map<S, S> m = match4(pat, s);
      if (m != null) l.add(m);
    }
    ret l;
  }
  
  static Map<S, S> match4(S pat, S s) {
    L<S> tok1 = parse3(pat), tok2 = parse3(s);
    if (tok1.size() != tok2.size()) ret null;
    new Map<S, S> m;
    for (int i = 1; i < tok1.size(); i += 2) {
      S t1 = tok1.get(i), t2 = tok2.get(i);
      if (isVar(t1))
        m.put(t1, t2);
      else if (!t1.equalsIgnoreCase(t2))
        ret null;
    }
    ret m;
  }
  
  static boolean isVar(S s) {
    ret s.startsWith("$") && s.length() > 1;
  }
  
  static S convert(S r, Map<S, S> matches) {
    L<S> tok = javaTokPlusPeriod(r);
    for (int i = 1; i < tok.size(); i += 2) {
      if (tok.get(i).startsWith("$")) {
        S m = matches.get(tok.get(i));
        if (m != null)
          tok.set(i, m);
      }
    }
    ret join(tok);
  }
  
  static void addStatement(S s) {
    for (S st : statements)
      if (match3(st, s))
        ret;
    statements.add(s);
  }
  
  static Lisp equ(O... args) { ret lisp("equ", args); }
  
  !include #2000515 // unquote
  !include #1001497 // parseBoolean
  !include #1000709 // formatSnippetID
}

Began life as a copy of #1001505