Ch 04

cc/ @fabioyamate @carlosgaldino.

Please review.
AFAIK pattern matching is done in sequence, so it will test from top to bottom.

if you have: `True vv _` as first expression, then the next one doesn't need to explicitly say that it is `False`, since it is the only option for `Bool` type.

So `_ vv True` would be sufficient as the third expression. Considering this, you could swap the second and third pattern matching, and let the last one as `_ vv _` because you don't care the values, since you already tested for `True` as left or right