feat(nullable): add mapWithDefault

Author: glennsl

src/Core__Nullable.mjs

@@ -36,10 +36,19 @@ function map(value, f) {
 
 }
 
+function mapWithDefault(value, $$default, f) {
+  if (value == null) {
+    return $$default;
+  } else {
+    return Curry._1(f, value);
+  }
+}
+
 export {
   fromOption ,
   getWithDefault ,
   getExn ,
   map ,
+  mapWithDefault ,
 }
 /* No side effect */

src/Core__Nullable.res

@@ -33,3 +33,9 @@ let map = (value, f) =>
   | Some(x) => Some(f(x))
   | None => None
   }
+
+let mapWithDefault = (value, default, f) =>
+  switch value->toOption {
+  | Some(x) => f(x)
+  | None => default
+  }