srecord noeq G22MeshMapper_v2(G22Mesh mesh1, G22Mesh mesh2) {
  // import the important classes
  delegate Anchor, Curve to G22Mesh.
  delegate mapAnchor, unmapAnchor, tempMapAnchor to mm.
  
  // params
  
  settable bool chooseAnchor1AtRandom;
  
  // output
  
  G22MeshMapping mm;
  
  // index structures
  
  MultiMap<Int, Anchor> anchorsByArity2;
    
  // EXCEPTIONS (e.g. meshes don't match in signature)
  
  // set to the reason why when a mapping is deemed impossible
  settable O rejectedBecause;
  
  bool rejected() { ret rejectedBecause != null; }
  
  // INTERNAL VARS
  
  bool prechecksDone;
  S sig1, sig2;
  Anchor anchor1; // first anchor to map
  
  G22MeshMapping get() { ret mm; }
  
  // Do the whole search, but in "random" mode (may fail)
  void run_random {
    search_step1();
    while (search_step2());
  }
  
  // random mode
  void search_step1() {
    prechecks(); if (rejected()) ret;
    
    // make empty mapping
    mm = new G22MeshMapping(mesh1, mesh2);
    
    anchorsByArity2 = multiMapIndex(mesh2.anchors(), a -> a.arity());
    
    // Choose first anchor to map - this is arbitrary
    // (not a backtracking point)
    Anchor anchor1 = chooseAnchor1AtRandom ? random(mesh1.anchors()) : first(mesh1.anchors());
    
    // Choose which anchor to map it to 
    // (first backtracking point)
    L<Anchor> options = anchorsByArity2.get(anchor1.arity());
    // ret BacktrackingOptions(options, ...); ???
    
    Anchor anchor2 = random(options);
    print("G22MeshMapper_v2 step1: Connecting " + anchor1 + " to " + anchor2);
    mapAnchor(anchor1, anchor2);
  }
  
  // random mode
  bool search_step2() {
    bool change;
    for (curve1 : mesh1.curves()) {
      // skip if curve is already mapped
      if (mm.isMapped(curve1))
        continue; // with print("Curve is mapped: " + curve1);
      
      print("Looking to match " + curve1);
      
      // check if anchors are mapped
      Anchor start2 = mm.get(curve1.start);
      Anchor end2 = mm.get(curve1.end);
      
      // If neither anchor is mapped, postpone this curve
      if (start2 == null && end2 == null)
        continue; // with print("Curve is not discovered yet: " + curve1);
      
      // Start at the mapped anchor, choose a viable curve in mesh2 to map to
      bool startAtEnd = end2 != null;
      Anchor a1 = curve1.anchor(startAtEnd);
      Anchor a1other = curve1.anchor(!startAtEnd);
      Anchor a2 = mm.get(curve1.anchor(startAtEnd));
      
      print(+a1);
      print(+a2);
      print(+a1other);
      
      new L<Curve> possibleCurves;
      for (c2 : a2.curves()) {
        if (mm.isMapped(c2))
          continue; // with print("Curve already mapped: " + c2);
        
        // check for arity match
        Anchor a3 = c2.anchorOpposite(a2);
        print(+a3);
        int arity1 = a3.arity(), arity2 = a1other.arity();
        if (arity1 != arity2)
          continue with print("Arity mismatch (" + arity1 + "/" + arity2 + ") for curve " + c2);
          
        // This curve is viable as a mapping target
        possibleCurves.add(c2);
      }
      
      print(l(possibleCurves) + "/" + l(a2.curves())
        + " possible curve(s) to map " + curve1 + " to:");
      pnl(possibleCurves);
      if (empty(possibleCurves))
        ret false with rejectedBecause("Could not map curve " + curve1);
        
      // Map the curve
      Curve c2 = random(possibleCurves);
      bool flipped = c2.start() != a2;
      print("Mapping curve " + curve1 + " to " + c2);
      mm.mapCurve(curve1, c2, flipped);
      set change;
    }
    
    ret change;
  }
  
  Search newSearch() {
    ret new Search;
  }
  
  // backtracking version
  class Search extends VStackComputableWithStep<Void> is IMakeEmptyClone {
    Anchor anchor2;
    
    public selfType makeEmptyClone() { ret new selfType; }
    
    void step(VStack stack) {
      cast stack to BStack<?>;
      
      if (step == 0) {
        prechecks();
        if (rejected()) stack.ret();
        step = 1;
      } else if (step == 1) {
        // make empty mapping
        mm = new G22MeshMapping(mesh1, mesh2);
        
        anchorsByArity2 = multiMapIndex(mesh2.anchors(), a -> a.arity());
        
        // Choose first anchor to map - this is arbitrary
        // (not a backtracking point)
        anchor1 = chooseAnchor1AtRandom ? random(mesh1.anchors()) : first(mesh1.anchors());
      
        // Choose which anchor to map it to (first backtracking point).
        // List should never be empty because we checked the signatures first.
        L<Anchor> anchor2options = anchorsByArity2.get(anchor1.arity());
        
        step = 2;
        stack.options(this, map(anchor2options, anchor2
          -> instance -> instance.anchor2 = anchor2));
      } else if (step == 2) {
        print("G22MeshMapper_v2 step1: Connecting " + anchor1 + " to " + anchor2);
        stack.temp(tempMapAnchor(anchor1, anchor2));
        step = 3;
      } else if (step == 3) {
        stack.call(new Step2);
        step = 4;
      } else {
        if (isTrue(stack.subResult()))
          step = 3;
        else
          stack.return();
      }
    }
  }
  
  class Step2 extends VStackComputableWithStep<Bool> is IMakeEmptyClone {
    bool change;
    Iterator<Curve> curve1iterator;
    Curve curve1, c2;
    Anchor a2;
    
    public selfType makeEmptyClone() { ret new selfType; }
    
    void step(VStack stack) {
      cast stack to BStack<?>;
      
      if (step == 0) {
        curve1iterator = iterator(mesh1.curves());
        step++;
      } else if (step == 1) {
        if (!curve1iterator.hasNext())
          ret with stack.return(change);

        curve1 = curve1iterator.next();
        
        print("Looking to match " + curve1);
      
        // skip if curve is already mapped
        if (mm.isMapped(curve1)) {
          print("Curve is mapped: " + curve1);
          ret; // continue loop
        }
        
        // check if anchors are mapped
        Anchor start2 = mm.get(curve1.start);
        Anchor end2 = mm.get(curve1.end);
      
        // If neither anchor is mapped, postpone this curve
        if (start2 == null && end2 == null) {
          //print("Curve is not discovered yet: " + curve1);
          ret; // continue loop;
        }
        
        // Start at the mapped anchor, choose a viable curve in mesh2 to map to
        bool startAtEnd = end2 != null;
        Anchor a1 = curve1.anchor(startAtEnd);
        Anchor a1other = curve1.anchor(!startAtEnd);
        a2 = mm.get(curve1.anchor(startAtEnd));
      
        print(+a1);
        print(+a2);
        print(+a1other);
      
        new L<Curve> possibleCurves;
        for (c2 : a2.curves()) {
          if (mm.isMapped(c2)) {
            //print("Curve already mapped: " + c2);
            continue; // continue loop
          }
          
          // check for arity match
          Anchor a3 = c2.anchorOpposite(a2);
          print(+a3);
          int arity1 = a3.arity(), arity2 = a1other.arity();
          if (arity1 != arity2) {
            print("Arity mismatch (" + arity1 + "/" + arity2 + ") for curve " + c2);
            continue; // continue loop
          }
            
          // This curve is viable as a mapping target
          possibleCurves.add(c2);
          print("Possible curve!");
        }
      
        print(l(possibleCurves) + "/" + l(a2.curves())
          + " possible curve(s) to map " + curve1 + " to: ");
        pnl(possibleCurves);
        if (empty(possibleCurves)) {
          stack.temp(tempRejectedBecause("Could not map curve " + curve1));
          ret with stack.ret(false);
        }
        
        // Go through all curve mappings
        step = 2;
        stack.options(this, map(possibleCurves,
          c2 -> instance -> instance.c2 = c2));
        ret;
      } else {
        bool flipped = c2.start() != a2;
        print("Mapping curve " + curve1 + " to " + c2);
        stack.temp(mm.tempMapCurve(curve1, c2, flipped));
        set change;
        
        // continue loop
        step = 1;
      }
    }
  }
  
  protected void prechecks {
    set prechecksDone;
    sig1 = mesh1.signature();
    sig2 = mesh1.signature();
    if (!eq(sig1, sig2))
      ret with rejectedBecause(G22SignatureMismatch(mesh1, mesh2));
  }
  
  AutoCloseable tempRejectedBecause(O reason) {
    rejectedBecause(reason);
    ret -> rejectedBecause(null);
  }
}

Began life as a copy of #1035369