Add Create A Map Of Strings as a reason 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/).
 
-_733 TILs and counting..._
+_734 TILs and counting..._
 
 ---
 
@@ -524,6 +524,7 @@ _733 TILs and counting..._
 - [Break Out Of A While Loop](reason/break-out-of-a-while-loop.md)
 - [Compile Reason To Native With Dune](reason/compile-reason-to-native-with-dune.md)
 - [Compile Reason With An OCaml Package Using Dune](reason/compile-reason-with-an-ocaml-package-using-dune.md)
+- [Create A Map Of Strings](reason/create-a-map-of-strings.md)
 - [Create A Stream From An Array](reason/create-a-stream-from-an-array.md)
 - [Creating A 2D Array](reason/creating-a-2d-array.md)
 - [Data Structures With Self-Referential Types](reason/data-structures-with-self-referential-types.md)

reason/create-a-map-of-strings.md

@@ -0,0 +1,28 @@
+# Create A Map Of Strings
+
+[ReasonML](https://reasonml.github.io/en) has the [`Map.Make`
+functor](https://reasonml.github.io/api/Map.Make.html) in its standard
+library which allows you to create a `Map` module with a specific key type.
+Here is how we can make a map module with string keys.
+
+```reason
+module StringMap = Map.Make(String);
+```
+
+We can then use that module to to create an empty map followed by adding
+key-value pairs to it.
+
+```
+StringMap.empty
+|> StringMap.add("Morty", "Smith")
+|> StringMap.add("Rick", "Sanchez")
+|> StringMap.add("Scary", "Terry")
+|> StringMap.iter((first, last) => {
+  print_endline(Printf.sprintf("%s %s", first, last));
+});
+/*
+Morty Smith
+Rick Sanchez
+Scary Terry
+*/
+```