add Iter::map_option

[Yoorkin]

Iter::map_option serves the same functionality as Array::map_option.

[peter-jerry-ye-code-review]

From the provided git diff output, here are three potential issues or areas of improvement in the MoonBit code:

1. Unused Function Parameter in map_option:
   In the map_option function, there is a parameter A that is used in the type signature but not directly used within the function body. This might be intentional if A is used indirectly through the closure f, but it could also be a potential oversight if A was meant to be used elsewhere.

   pub fn map_option[A, B](self : Iter[A], f : (A) -> B?) -> Iter[B] {
     fn(yield) {
       self.run(
         fn(a) {
           match f(a) {
             Some(b) => yield(b)
             None => IterContinue
           }
         },
       )
     }
   }
   

2. Lack of Error Handling in map_option:
   The map_option function uses IterContinue to handle the case where the mapping function returns None. This is a valid approach in this context, but it might be worth adding a comment to explain why IterContinue is used instead of another approach, especially since MoonBit supports error handling constructs like raise.

   match f(a) {
     Some(b) => yield(b)
     None => IterContinue // Consider adding a comment explaining why IterContinue is used
   }
   

3. Inconsistent Naming Convention in Tests:
   The test function names in iter_test.mbt are inconsistent. For example, map is named directly after the function being tested, while map_option is named with additional context (map_option). It might be beneficial to standardize the naming convention for better readability and consistency.

   test "map" {
     ...
   }
   
   test "map_option" { // Consider renaming to "map_option" or adding more context
     ...
   }
   

These suggestions aim to improve clarity, consistency, and potential robustness of the code.

[coveralls]

Pull Request Test Coverage Report for Build 3670

Details

• 5 of 5 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 82.761%

---

Totals
Change from base Build 3667:	0.02%
Covered Lines:	4263
Relevant Lines:	5151

---

💛 - Coveralls