### Comparing flip compare

GHCmod-vim hinted at an improvement in some code I was writing:

`reverse $ sort`

why not `sortBy (flip compare)`

So I looked at the type signatures for each of these.

```
λ > :t reverse $ sort
λ > Ord a => [a] -> [a]
λ > :t sortBy
λ > (a -> a -> Ordering) -> [a] -> [a]
λ > :t (flip compare)
λ > Ord b => b -> b -> Ordering
```

`flip`

is just `f x y = f y x`

A little reminder of how `compare`

works:

```
λ > compare 1 2
λ > LT
λ > flip compare 1 2
λ > GT
```

This is the part that wasn’t obvious to me; that by simply flipping the
comparison we’re reversing the resulting sorted list.
At that point we can see that `sortBy`

is traversing the list once whereas
`reverse $ sort`

is running through the list twice.