Added a circular buffer data structure

ds/circular.scm

@@ -0,0 +1,44 @@
+;; A very simple and non-evolved, fixed-size circular buffer based on a vector
+
+(export make-circular-buffer
+        circular-buffer-length
+        circular-buffer-fill!
+        circular-buffer-push!
+        circular-buffer-first
+        circular-buffer-last)
+
+(define-type circular-buffer
+  constructor: make-circular-buffer-internal
+  (vec read-only:)
+  pos)
+
+(define (make-circular-buffer size #!optional (init 0))
+  (make-circular-buffer-internal (make-vector size init)
+                                 0))
+
+(define (circular-buffer-length buf)
+  (vector-length
+   (circular-buffer-vec buf)))
+
+(define (circular-buffer-fill! buf val)
+  (vector-fill! (circular-buffer-vec buf)
+                val))
+
+(define (circular-buffer-push! buf val)
+  (let* ((vec (circular-buffer-vec buf))
+         (new-pos (modulo (+ 1 (circular-buffer-pos buf))
+                          (vector-length vec))))
+    (circular-buffer-pos-set! buf new-pos)
+    (vector-set! vec new-pos val)))
+
+(define (circular-buffer-ref buf pos)
+  (let ((vec (circular-buffer-vec buf)))
+    (vector-ref vec
+                (modulo pos
+                        (vector-length vec)))))
+
+(define (circular-buffer-first buf)
+  (circular-buffer-ref buf 0))
+
+(define (circular-buffer-last buf)
+  (circular-buffer-ref buf -1))