* Write a function `unmap2` that is something like the inverse of `map2`. This function expects two arguments, the second being a sequence of elements of some type *t*. The first is a function `g` that expects a single argument of type *t* and returns a *pair* of results, rather than just one result. We want to collate these results, the first into one list, and the second into a different list. Then `unmap2` should return those two lists. Thus if:
- g x1 # evaluates to [y1, z1]
- g x2 # evaluates to [y2, z2]
- g x3 # evaluates to [y3, z3]
+ g z1 # evaluates to [x1, y1]
+ g z2 # evaluates to [x2, y2]
+ g z3 # evaluates to [x3, y3]
- Then `unmap2 (g, [x1, x2, x3])` should evaluate to `([y1, y2, y3], [z1, z2, z3])`.
+ Then `unmap2 (g, [z1, z2, z3])` should evaluate to `([x1, x2, x3], [y1, y2, y3])`.
* Write a function `takewhile` that expects a `p` argument like `filter`, and also a sequence. The result should behave like this: