Add Create A Stream From An Array as a reasonml til

README.md

@@ -10,7 +10,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 For a steady stream of TILs from a variety of rocketeers, checkout
 [til.hashrocket.com](https://til.hashrocket.com/).
 
-_685 TILs and counting..._
+_686 TILs and counting..._
 
 ---
 
@@ -502,6 +502,7 @@ _685 TILs and counting..._
 ### ReasonML
 
 - [Break Out Of A While Loop](reason/break-out-of-a-while-loop.md)
+- [Create A Stream From An Array](reason/create-a-stream-from-an-array.md)
 - [Defining Variants With Constructor Arguments](reason/defining-variants-with-constructor-arguments.md)
 - [Dynamically Create A Printf String Format](reason/dynamically-create-a-printf-string-format.md)
 - [Exhaustive Pattern Matching Of List Variants](reason/exhaustive-pattern-matching-of-list-variants.md)

reason/create-a-stream-from-an-array.md

@@ -0,0 +1,35 @@
+# Create A Stream From An Array
+
+There are functions in the [`Stream`
+module](https://reasonml.github.io/api/Stream.html) for turning a variety of
+data structures into streams -- lists, input channels, etc.
+
+What if you have an array?
+
+The `Stream.from` function lets you define a function for custom fitting
+data structures into streams. Let's take a look:
+
+```reason
+let pokemon = [| "bulbasaur", "charmander", "squirtle" |];
+
+let poke_stream: Stream.t(string) =
+  Stream.from(i =>
+    switch (pokemon[i]) {
+    | pokemon => Some(pokemon)
+    | exception (Invalid_argument("index out of bounds")) => None
+    }
+  );
+```
+
+The function takes the current index and needs to either return `Some('a)`
+with the corresponding value or `None` if the stream is empty.
+
+With that, we now have a stream on which we can invoke any of the stream
+functions.
+
+```reason
+switch (Stream.next(poke_stream)) {
+| pokemon => print_endline(Printf.sprintf("Next Pokemon: %s", pokemon))
+| exception Stream.Failure => print_endline("No pokemon left")
+};
+```