## Introduction
Add a few more functional sequence utilities to the standard library.
## Motivation
We have map, filter, and reduce, but we're missing a bunch of useful
utilities like scan, iterate, takeWhile, and dropWhile. Interestingly,
the stdlib includes an implementation of scan in the doc comment for
LazySequenceType, it just doesn't actually provide it as API.
One of my concerns here is that while map, filter, and reduce are mostly
“lingua franca” terms-of-art among programmers everywhere, these others
are much less commonly-known and some of them aren't very descriptive of
what they do. There are lots more like these in the FP lexicon. It was
easy to draw the line at map/filter/reduce (which also don't follow the
usual grammar for API guidelines), but if we take the ones in this
proposal, where do we stop?
Because your PR has comments describing these methods (i.e. it's more
complete) I'll leave further remarks there.