title: Sparse arrays in Haskell?
body: <p>Is there any standard or "most usual" way to represent multidimensional sparse arrays in Haskell (without sacrificing performance too much)?</p>
  
  <p>Something like map&lt; int, map&lt; int, MyClass> > in C++, for example. I've Googled and found just some old academic papers and other people asking for this too.</p>
  
  <p>Thanks!</p>