Merge pull request #32 from johnhaley81/add-all

Add all part deux

README.md

@@ -87,6 +87,7 @@ Core functions. **Note:** `_` represents the future itself as inserted by `->` (
 - `Future.flatMap(_,fn)` - Transform a future value into another future value
 - `Future.get(_,fn)` - Get the value of a future
 - `Future.tap(_,fn)` - Do something with the value of a future without changing it. Returns the same future so you can continue using it in a pipeline. Convenient for side effects such as console logging.
+- `Future.all(_,fn)` - Turn a list of futures into a future of a list.  Used when you want to wait for a collection of futures to complete before doing something (equivalent to Promise.all in Javascript).
 
 ### Belt.Result
 

src/Future.re

@@ -49,6 +49,16 @@ let map4 = (fa, fb, fc, fd, f) => map3(map2(fa, fb, f), fc, fd, v => v);
 let map5 = (fa, fb, fc, fd, fe, f) =>
   map4(map2(fa, fb, f), fc, fd, fe, v => v);
 
+let rec all = futures =>
+  switch (futures) {
+  | [head, ...tail] =>
+    all(tail)
+    ->flatMap(tailResult =>
+        head->map(headResult => [headResult, ...tailResult])
+      )
+  | [] => value([])
+  };
+
 let tap = (Future(get) as future, f) => {
   get(f);
   future;

tests/TestFuture.re

@@ -103,6 +103,16 @@ describe("Future", () => {
 
     future->Future.get(_ => done_());
   });
+
+  testAsync("all (async)", done_ =>
+    Future.all([Future.value(1), delay(25, () => 2), delay(50, () => 3)])
+    ->Future.get(result =>
+        switch (result) {
+        | [1, 2, 3] => done_()
+        | _ => raise(TestError("Expected [1, 2, 3]"))
+        }
+      )
+  );
 });
 
 describe("Future Belt.Result", () => {