I am wondering if it is possible to iterate over pairs of the previous and the current element in an iterable collection. Eg to implement

```
function pairs_sum(s)
result = []
state = start(s)
while !done(s, state)
(i, next_state) = next(s, state)
push!(result, state+next_state)
state = next_state
end
result
end
```

as

```
pairs_sum(s) = [sum(e) for e in (magic here)]
```

with seeing each element only once, so

```
pairs_sum(s) = [sum(e) for e in zip(s, drop(s,1))]
```

doesn’t count.