walk sequence of range boundaries values for source and filter ranges

add lower level logic for walking the boundary markers of sets
but distinguish between a source range and a filter range when
looking at the start and end boundary behavior

src/challenge/discrete_value_range.clj

@@ -1,4 +1,5 @@
-(ns challenge.discrete-value-range)
+(ns challenge.discrete-value-range
+  (:require [clojure.core.match :refer [match]]))
 
 (defprotocol DiscreteValueRange
   "A protocol for generic behavior on Ranges over
@@ -29,7 +30,7 @@
   (start [this])
   (end [this])
   (range-type [this])
-  (union [range1 range2]))
+  (union [this other]))
 
 (defn- ordered-range-values
   "Builds an ordered list or 'fenceposts' for the start and end
@@ -129,4 +130,51 @@
    (combine-abutting-ranges)))
 
 (defn consolidate [ranges]
-  (eduction consolidate-ranges-xf (ordered-range-values ranges)))
+  (into #{} consolidate-ranges-xf (ordered-range-values ranges)))
+
+(defn walk-range-boundaries [range-boundary-items]
+  (let [close-working-range (fn [range-type start end ranges]
+                              (conj ranges (->discrete-value-range range-type
+                                                                   start
+                                                                   end)))]
+
+    (loop [[boundary-item & boundary-items] range-boundary-items
+           in-filter-range nil
+           in-source-range nil
+           ranges #{}
+           close-fn nil]
+      (match [boundary-item]
+        [nil]
+        ranges
+
+        [{:boundary-type :start
+          :range-source-type :source-range
+          :type range-type
+          :value new-working-range-start-value}]
+        (recur boundary-items in-filter-range true ranges (partial close-working-range
+                                                                   range-type
+                                                                   new-working-range-start-value))
+
+        [{:boundary-type :end
+          :range-source-type :source-range
+          :value value}]
+        (if in-filter-range
+          (recur boundary-items in-filter-range false ranges nil)
+          (recur boundary-items in-filter-range false (close-fn value ranges) nil))
+
+        [{:boundary-type :start
+          :range-source-type :filter-range
+          :prev-value prev-value}]
+        (if close-fn
+          (recur boundary-items true in-source-range (close-fn prev-value ranges) nil)
+          (recur boundary-items true in-source-range ranges close-fn))
+
+        [{:boundary-type :end
+          :range-source-type :filter-range
+          :type range-type
+          :next-value new-working-range-start-value}]
+        (if in-source-range
+          (recur boundary-items false in-source-range ranges (partial close-working-range
+                                                                      range-type
+                                                                      new-working-range-start-value))
+          (recur boundary-items false in-source-range ranges close-fn))))))