Hello!
I've got a task where I need to process a sequence of elements pairwise,
while collecting the (possibly mutated) elements into a new sequence.
The neighboring elements may affect each other, hence the need for mutation.
I searched through the help system looking for words similar to each-pair or
each2, to no avail.
Here's what I came up with:
```
:: each2* ( seq quot: ( prev next -- next' ) -- )
seq unclip-slice :> elt! quot '[ elt @ elt! ] each ; inline
```
What I want to happen is this:
```
{ 1 2 3 } [ [ swap . . nl ] keep 10 + ] each2*
1
2
12
3
```
So that the quotation passed to `each2*` would walk through all consecutive
pairs of the elements in `seq`, but would also be able to mutate the `next`
element for its next iteration.
Now, I have no experience with functional languages (in fact, that's why I'm
studying Factor, so feel free to correct me), but my suspicion is that I
inadvertently created a closure over the `elt` variable, because instead of the
expected output I get the following:
```
{ 1 2 3 } [ [ swap . . nl ] keep 10 + ] each2*
1
2
1
3
```
By using the walker I see that the initial value of `elt` is curried to the
quotation, so the subsequent `elt!` has no effect.
Please, tell me: is this the intended interaction between the locals and the
fry, or is it an optimization gone wrong?
And how do I get the behavior that I want from the `each2*`? Is there a
totally different approach that I missed? My intention is to use `each2*`
inside the `make` call to construct the result I need.
Thank you!
---=====---
Александр
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