Add a couple of procedures for generating histogram buckets

1 files changed, 41 insertions, 0 deletions

diff --git a/prometheus.scm b/prometheus.scm
index 2a181f8..9d8d7ad 100644
--- a/prometheus.scm
+++ b/prometheus.scm
@@ -164,6 +164,47 @@ list of label names to be permitted for this metric and
   ;; The default buckets used in other client libraries
   (list 0.005 0.01 0.025 0.05 0.1 0.25 0.5 1 2.5 5 10 (inf)))
 
+(define* (linear-histogram-buckets #:key start step end count)
+  (when (and end count)
+    (raise-exception
+     (make-exception-with-message
+      "you can only specify either end or count to linear-histogram-buckets")))
+
+  (append (if count
+              (map (lambda (index)
+                     (+ start
+                        (* step index)))
+                   (iota count))
+              (let loop ((reverse-result (list start))
+                         (current-value start))
+                (let ((next-value (+ current-value step)))
+                  (if (>= next-value end)
+                      (reverse (cons end reverse-result))
+                      (loop (cons next-value reverse-result)
+                            next-value)))))
+          (list (inf))))
+
+(define* (exponential-histogram-buckets #:key start (factor 2) end count)
+  (when (and end count)
+    (raise-exception
+     (make-exception-with-message
+      "you can only specify either end or count to exponential-histogram-buckets")))
+
+  (append (if count
+              (map (lambda (index)
+                     (* start
+                        (expt factor index)))
+                   (iota count))
+              (let loop ((reverse-result (list start)))
+                (let ((next-value
+                       (* start
+                          (expt factor
+                                (+ 1 (length reverse-result))))))
+                  (if (>= next-value end)
+                      (reverse (cons end reverse-result))
+                      (loop (cons next-value reverse-result))))))
+          (list (inf))))
+
 (define* (make-histogram-metric registry name
                                 #:key
                                 (buckets %default-histogram-buckets)