Introduce stream-split-by.

This procedure isn't currently used, but as noted is really useful for
grouping a character stream into a word stream, which is a later commit
will use for it for justifying posibly infinite streams of text.

1 files changed, 14 insertions, 1 deletions

diff --git a/module/srfi/srfi-41/util.scm b/module/srfi/srfi-41/util.scm
index cecbb3b3..1571cc4c 100644
--- a/module/srfi/srfi-41/util.scm
+++ b/module/srfi/srfi-41/util.scm
@@ -18,7 +18,8 @@
            stream-partition
            stream-split
            stream-paginate
-           stream-timeslice-limit))
+           stream-timeslice-limit
+           stream-split-by))
 
 (define (stream-car+cdr stream)
   (values (stream-car stream)
@@ -146,3 +147,15 @@
           (stream-timeslice-limit (stream-cdr strm) timeslice)))
    (lambda _ stream-null)))
 
+
+(define-stream (stream-split-by pred strm)
+  (let loop ((accumulated '())
+             (strm strm))
+    (stream-match strm
+      (() (if (null? accumulated)
+              stream-null
+              (stream (reverse accumulated))))
+      ((x . xs) (pred x)
+       (stream-cons (reverse (cons x accumulated)) (loop '()  xs)))
+      ((x . xs)
+       (loop (cons x accumulated) xs)))))