Actually implement range-set-span

Guess I never got around to doing this.

collection/private/endpoint-map-range-set.rkt

@@ -85,7 +85,7 @@
      (endpoint-map-range-containing-or-absent (this-endpoints this) (this-comparator this) value))
 
    (define (range-set-span-or-absent this)
-     (endpoint-map-span-or-absent (this-endpoints this)))
+     (endpoint-map-span-or-absent (this-endpoints this) (this-comparator this)))
 
    (define (range-subset this subset-range)
      (define cut-comparator (cut<=> (range-comparator subset-range)))
@@ -287,7 +287,7 @@
      (endpoint-map-range-containing-or-absent (this-endpoints this) (this-comparator this) value))
 
    (define (range-set-span-or-absent this)
-     (endpoint-map-span-or-absent (this-endpoints this)))
+     (endpoint-map-span-or-absent (this-endpoints this) (this-comparator this)))
 
    (define (range-subset this subset-range)
      TODO)]
@@ -369,8 +369,12 @@
    (λ (nearest-range) (range-contains? nearest-range value))))
 
 
-(define (endpoint-map-span-or-absent endpoints)
-  TODO)
+(define/guard (endpoint-map-span-or-absent endpoints comparator)
+  (guard (sorted-map-empty? endpoints) then
+    absent)
+  (match-define (present lower-cut) (sorted-map-least-key endpoints))
+  (match-define (present (entry _ upper-cut)) (sorted-map-greatest-entry endpoints))
+  (present (range-from-cuts lower-cut upper-cut #:comparator comparator)))
 
 
 (define/guard (endpoint-map-get-nearest-range endpoints comparator cut)

collection/range-set.rkt

@@ -593,4 +593,18 @@
       (test-case "remove span enclosing range"
         (define actual (range-set-remove ranges (closed-range 2 25)))
         (define expected (range-set #:comparator real<=>))
-        (check-equal? actual expected)))))
+        (check-equal? actual expected))))
+
+  (test-case (name-string range-set-span)
+
+    (test-case "closed ranges"
+      (define actual (range-set-span (range-set (closed-range 2 5) (closed-range 7 10))))
+      (check-equal? actual (closed-range 2 10)))
+
+    (test-case "open ranges"
+      (define actual (range-set-span (range-set (open-range 2 5) (open-range 7 10))))
+      (check-equal? actual (open-range 2 10)))
+
+    (test-case "closed and open ranges"
+      (define actual (range-set-span (range-set (closed-range 2 5) (open-range 7 10))))
+      (check-equal? actual (closed-open-range 2 10)))))

collection/range-set.scrbl

@@ -7,6 +7,7 @@
                      racket/sequence
                      racket/set
                      rebellion/base/comparator
+                     rebellion/base/option
                      rebellion/base/range
                      rebellion/collection/range-set
                      rebellion/streaming/reducer
@@ -268,7 +269,7 @@ descending order, use @racket[in-range-set] with @racket[#:descending?] set to t
 
  @(examples
    #:eval (make-evaluator) #:once
-   (range-set-span (range-set (closed-range 2 5) (oepn-range 9 10)))
+   (range-set-span (range-set (closed-range 2 5) (open-range 9 10)))
    (eval:error (range-set-span (range-set #:comparator real<=>)))
    (range-set-span (range-set #:comparator real<=>) "empty range set!"))}
 
@@ -280,7 +281,7 @@ descending order, use @racket[in-range-set] with @racket[#:descending?] set to t
 
  @(examples
    #:eval (make-evaluator) #:once
-   (range-set-span-or-absent (range-set (closed-range 2 5) (oepn-range 9 10)))
+   (range-set-span-or-absent (range-set (closed-range 2 5) (open-range 9 10)))
    (range-set-span-or-absent (range-set #:comparator real<=>)))}