select: Make promise cancellable.

lib/index.js

@@ -309,31 +309,34 @@ Channel.of = (...values) =>
 Channel.isChannel = (arg) =>
   prototype.isPrototypeOf(arg)
 
-Channel.select = (...methodPromises) => {
-  const promise = new Promise((resolve, reject) => {
-    methodPromises.forEach(async (promise) => {
-      promise.prethen(() => {
-        // We've been given a heads-up that this method will complete first so
-        // cancel the other method calls.
-        methodPromises.forEach((other) => {
-          if (other !== promise) {
-            other.cancel()
-          }
+Channel.select = (...methodPromises) =>
+  Object.assign(
+    new Promise((resolve, reject) => {
+      methodPromises.forEach(async (promise) => {
+        promise.prethen(() => {
+          // We've been given a heads-up that this method will complete first so
+          // cancel the other method calls.
+          methodPromises.forEach((other) => {
+            if (other !== promise) {
+              other.cancel()
+            }
+          })
         })
+
+        try {
+          await promise
+        } catch (exception) {
+          reject(exception)
+        }
+
+        resolve(promise.channel)
       })
-
-      try {
-        await promise
-      } catch (exception) {
-        reject(exception)
-      }
-
-      resolve(promise.channel)
-    })
-  })
-
-  return promise
-}
+    }),
+    {
+      cancel: () =>
+        Promise.all(methodPromises.map((promise) => promise.cancel()))
+    }
+  )
 
 // functional interface allowing full or partial application
 //