com.twitter.summingbird.planner.DagOptimizer
If the given Id can be replaced with a simpler expression, return Some(expr) else None.
If the given Id can be replaced with a simpler expression, return Some(expr) else None.
If it is convenient, you might write a partial function and then call .lift to get the correct Function type
a.flatMap(fn).flatMap(fn2) can be written as a.flatMap(compose(fn, fn2))