Attached is a patch to implement the changes detailed in
http://srfi-email.schemers.org/srfi-41/msg/3066997, which improves
the performance of `stream-constant` compared to the reference
implementation.
It probably doesn't improve performance against the Guile version
(which is already O(1) per element), but it's a cleaner implementation
that removes the need for the `list?` shadowing hack in `list->stream`.
This also removes support for circular lists for `list->stream` (which
was never supported in the reference implementation, and was added as
an implementation detail of `stream-constant` (which I originally
implemented using circular lists).
Comments welcome.
Cheers,
Chris.
--- Begin Message ---
See http://srfi-email.schemers.org/srfi-41/msg/3066997 for more details.
---
module/srfi/srfi-41.scm | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/module/srfi/srfi-41.scm b/module/srfi/srfi-41.scm
index 3589b35..59c3b50 100644
--- a/module/srfi/srfi-41.scm
+++ b/module/srfi/srfi-41.scm
@@ -212,8 +212,6 @@
((letrec ((tag (stream-lambda (name ...) body1 body2 ...))) tag) val ...))
(define (list->stream objs)
- (define (list? x)
- (or (proper-list? x) (circular-list? x)))
(must list? objs 'list->stream "non-list argument")
(stream-let recur ((objs objs))
(if (null? objs) stream-null
@@ -274,7 +272,9 @@
(define stream-constant
(case-lambda
(() stream-null)
- (objs (list->stream (apply circular-list objs)))))
+ ((obj) (stream-let loop () (stream-cons obj (loop))))
+ (objs (define strm (list->stream objs))
+ (stream-let loop () (stream-append strm (loop))))))
(define-syntax* (stream-do x)
(define (end x)
--
2.3.8 (Apple Git-58)
--- End Message ---
