Gensym offers a simple facility for generating fresh integer identifiers.
A gensym is a generator of unique integer identifiers.
make() produces a new gensym.
val make : unit -> gensymA slightly more powerful abstraction is a generator whose current state can be inspected (without modification).
generator() creates a new generator. fresh generator causes the generator to create and return a fresh integer identifier. current
generator returns the generator's current state, that is, the next available integer identifier.
val generator : unit -> generatorval fresh : generator -> intval current : generator -> int