Given two arrays, return all pairs (where each number is in each array) whose sum is an odd number.

odd_sum.gleam

import gleam/list
import gleam/result

pub fn oddsum(arr1, arr2) {
 list.map(arr1, fn(a) {
  list.map(arr2, fn(b) { [a, b]})}) |> list.flatten |>  list.map(fn(x){
  case {{result.unwrap(list.first(x), 0) + result.unwrap(list.last(x), 0)} % 2} {
  1 -> x
  _ -> []
  }
  }) |> list.filter(fn(y){list.length(y) > 1})
}

pub fn main() {
  oddsum([9, 14, 6, 2, 11], [8, 4, 7, 20])|> echo
  oddsum([10, 12, 14, 18, 20], [2, 4, 6, 8])|> echo
  
}

output.txt

src/main.gleam:15
[[9, 8], [9, 4], [9, 20], [14, 7], [6, 7], [2, 7], [11, 8], [11, 4], [11, 20]]
src/main.gleam:16
[]