Stream: beginners

Topic: Access elements of Pair

Nils Hjelte (Sep 08 2024 at 15:38):

How do I access elements of Pair? Eg as used in the example of map2, zipped = List.map2 ["a", "b", "c"] [1, 2, 3] Pair. If I pipe this to List.all how do I unpack/destructure the elements of the pair? I tried \p -> p.0 == p.1 which seems to be tuple unpacking, and \p -> p.first == p.second, which tries to bind to a record with members first/second. (my example has integers in both lists, not string and int like the map2 example, so equality testing should be ok)

Brendan Hansknecht (Sep 08 2024 at 16:03):

So you used a tag as your map2 joining function

Brendan Hansknecht (Sep 08 2024 at 16:04):

So you have created Pair Str (Num a)

Brendan Hansknecht (Sep 08 2024 at 16:05):

So you would destructive the pair something like \Pair str int -> ...

Brendan Hansknecht (Sep 08 2024 at 16:07):

Also, you can destructive with a record or tuple as well:
\{first, second} -> ...
\(first, second) -> ...

Brendan Hansknecht (Sep 08 2024 at 16:08):

With the record, the names would need to match the field name

Brendan Hansknecht (Sep 08 2024 at 16:09):

For tags and tuples, the name can be anything

Brendan Hansknecht (Sep 08 2024 at 16:11):

And of course, instead of using Pair, you could just build a tuple or record:
List.map2 ["a", ...] [1, ...] \a, b -> (a, b)

Isaac Van Doren (Sep 08 2024 at 20:22):

If you use a tuple, you can access the fields with .0, .1, .2, etc:

("hello", "world").1 == "world"

List.map [("hello", "world")] .1 == ["world"]

Last updated: Nov 09 2025 at 12:14 UTC