feat(option): add zip

Author: glennsl

src/Core__Option.mjs

@@ -128,6 +128,16 @@ function cmp(a, b, f) {
   }
 }
 
+function zip(a, b) {
+  if (a !== undefined && b !== undefined) {
+    return [
+            Caml_option.valFromOption(a),
+            Caml_option.valFromOption(b)
+          ];
+  }
+  
+}
+
 export {
   some ,
   flat ,
@@ -144,5 +154,6 @@ export {
   isNone ,
   eq ,
   cmp ,
+  zip ,
 }
 /* No side effect */

src/Core__Option.res

@@ -125,3 +125,9 @@ let cmpU = (a, b, f) =>
   }
 
 let cmp = (a, b, f) => cmpU(a, b, (. x, y) => f(x, y))
+
+let zip = (a, b) =>
+  switch (a, b) {
+  | (Some(a), Some(b)) => Some(a, b)
+  | _ => None
+  }

src/Core__Option.resi

@@ -290,3 +290,15 @@ cmp(None, None, clockCompare) // 0
 ```
 */
 let cmp: (option<'a>, option<'b>, ('a, 'b) => int) => int
+
+/**
+`zip(a, b)` combines the values contained in `a` and `b` if both are `Some`, returns `None` otherwise..
+
+## Examples
+
+```rescript
+Option.zip(Some(1), Some(2)) // Some(1, 2)
+Option.zip(Some(1), None) // None
+```
+*/
+let zip: (option<'a>, option<'b>) => option<('a, 'b)>