structuralInvariant for MyersStack
look into FIXMEs
add docs to the implementations to help decide when to use which ones
put together some kind of benchmarking
use 'assert' to check preconditions?
find or reimplement the data structures from Martin Holter's thesis.
add mapAccum?
Add "Generic" versions of data structures requiring particular
  types of keys?
fix the test suite so it actually will finish compiling
  perhaps do a code generation phase to put the test for each
  module in its own test module?