static <A, B> Matrix<B> lambdaMapLike mapMatrix(IF1<A, B> f, Matrix<A> m) {
  if (m == null) null;
  
  class MappedMatrix extends AbstractMatrix<B> {
    *() { super(m.getWidth(), m.getHeight()); }
    
    public B get(int x, int y) { ret f.get(m.get(x, y)); }
    public void set(int x, int y, B a) { unimplemented(); }
  }
  
  ret new MappedMatrix;
}

Began life as a copy of #1003239