Add Create A Map Of Strings as a reason til

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
+*/
+```