Cleaning out our office at work, we’re moving down the road - found these relics
Heath
@heathhenley.dev
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Señor Application Engineer at a small sonar shop. Writing about things here: heathhenley.dev
Señor Application Engineer at a small sonar shop. Writing about things here: heathhenley.dev
![Ocaml code to map and fold a function over a list at the same time:
```ocaml
let map_and_fold ~f ~init lst =
let acc_ref = ref init in
let[@tail_mod_cons] rec go = function
| [] -> []
| hd :: tl ->
let b, new_acc = f hd !acc_ref in
acc_ref := new_acc;
b :: go tl
in
(go lst, !acc_ref)
```](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:k5vlsz32mm2nub75i53ztcut/bafkreiceytrgg44mqjpyruaxokhqg75w7vlph7s6zqkxlx4lfrdrzffele)
 -> list[list[T]]:
def inner(prev, results, orig_lst):
match orig_lst:
case []:
return [(prev + [x])] + results
case [first, *rest]:
return inner(prev + [first], [(prev + [x] + orig_lst)] + results, rest)
return inner([], [], lst)
def permutations_full_recursive[T](
lst: list[T], r: int | None = None) -> Generator[list[T]]:
r = len(lst) if r is None else r
if r == 0:
yield []
return
if not lst or r > len(lst):
return
match lst:
case [x] if r == 1:
yield [x]
case [first, *rest]:
# permutations of size r with first in them
yield from reduce(
lambda acc, p: acc + insert_all_positions(first, p),
permutations_full_recursive(rest, r - 1),
[]
)
# permutations of size without first in them
yield from permutations_full_recursive(rest, r)
```](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:k5vlsz32mm2nub75i53ztcut/bafkreia5oxbpkco4keazrhfb5tr4hj4pc7nt6alg6udgthnsp7ubxd6i6m)
![Results from running the code in utop on the list 1, 2, 3 with the map function (fun l a -> (l, a + 1)) - it should return the ([1; 2; 3], 3) but it returns ([1; 2; 3], 0)](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:k5vlsz32mm2nub75i53ztcut/bafkreigix2ww3iq6xpnoku5tuq7h7puhw7yvolbnr56ggwtmxdf2mq5ihu)
