Implement ldict-ref.

doc/utils.md

@@ -62,6 +62,17 @@ Returns ```#t``` if given dictionary contains no keys.
 
 Returns ```#t``` if given ```ld``` contains given key ```k```.
 
+    (ldict-ref ld k [default])
+
+* ```ld``` - a ldict instance
+* ```k``` - a compatible key
+* ```default``` - optional fallback value
+
+Retrieves the value associated with given key in given dictionary. If
+the dictionary does not contain it and no default is given, an
+exception is raised. Otherwise the default value is returned in case
+of missing key.
+
 ### IO
 
     (import util-io)