dhall-1.3.0: Prelude/Natural/sum

{-
Add all the numbers in a `List`

Examples:

```
./sum ([+2, +3, +5] : List Natural) = +10

./sum ([] : List Natural) = +0
```
-}
let sum : List Natural → Natural
    =   λ(xs : List Natural)
    →   List/fold Natural xs Natural (λ(l : Natural) → λ(r : Natural) → l + r) +0

in  sum