Started work on stream interleaving.

1 files changed, 24 insertions, 0 deletions

diff --git a/srfi/srfi-41/util.scm b/srfi/srfi-41/util.scm
new file mode 100644
index 00000000..ed378ea4
--- /dev/null
+++ b/srfi/srfi-41/util.scm
@@ -0,0 +1,24 @@
+(define-module (srfi srfi-41 util)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-41)
+  #:use-module (util) ; let*, find-min
+  #:export (stream-car+cdr interleave-streams))
+
+(define (stream-car+cdr stream)
+  (values (stream-car stream)
+          (stream-cdr stream)))
+
+;; Merges a number of totally ordered streams into a single
+;; totally ordered stream.
+;; ((≺, stream)) → (≺, stream)
+(define (interleave-streams < streams)
+  ;; Drop all empty streams
+  (let ((streams (remove stream-null? streams)))
+    ;; If all streams where empty, end the output stream
+    (if (null? streams)
+        stream-null
+        (let* ((min other (find-min < stream-car streams))
+               (m ms (stream-car+cdr min)))
+          (stream-cons m (interleave-streams < (cons ms other)))))))
+
+;;; Varför är allting så långsamt‽‽‽‽‽‽‽‽