Implement and document predicates for ldict and lset.

doc/utils.md

@@ -49,6 +49,12 @@ populating it with initial data.
 If only one argument is given, the procedure checks whether it is a
 list of equality procedure and acts accordingly.
 
+    (ldict? v)
+
+* ```v``` - any value
+
+Returns ```#t``` if given value is a ldict.
+
     (ldict-empty? ld)
 
 * ```ld``` - a ldict instance
@@ -213,6 +219,12 @@ This module implements linear-time set with custom comparator.
 
 Creates new lset with given comparator.
 
+    (lset? v)
+
+* ```v``` - any value
+
+Returns ```#t``` if given value is a lset.
+
     (lset-empty? ls)
 
 * ```ls``` - lset instance