Implement STREAM-LAST-PAIR.

diff --git a/v7/src/runtime/runtime.pkg b/v7/src/runtime/runtime.pkg
index 2dd9df6200e35ee2e43a6068077f4597a0b0f46a..b4f0aec380a1b8dfa49f54bb5d6f3065416fa5de 100644 (file)
--- a/v7/src/runtime/runtime.pkg
+++ b/v7/src/runtime/runtime.pkg
@@ -1,6 +1,6 @@
 #| -*-Scheme-*-
 
-$Id: runtime.pkg,v 14.460 2003/09/30 03:39:10 cph Exp $
+$Id: runtime.pkg,v 14.461 2003/09/30 04:22:52 cph Exp $
 
 Copyright 1988,1989,1990,1991,1992,1993 Massachusetts Institute of Technology
 Copyright 1994,1995,1996,1997,1998,1999 Massachusetts Institute of Technology
@@ -3783,6 +3783,7 @@ USA.
          stream-first
          stream-for-each
          stream-head
+         stream-last-pair
          stream-length
          stream-map
          stream-null?

diff --git a/v7/src/runtime/stream.scm b/v7/src/runtime/stream.scm
index 3b3aecf34982c4ddd03b5ccbee1a870df39fcc14..2a0c6d50d2d7c845b4bd32aca545558dd702e3e3 100644 (file)
--- a/v7/src/runtime/stream.scm
+++ b/v7/src/runtime/stream.scm
@@ -1,6 +1,6 @@
 #| -*-Scheme-*-
 
-$Id: stream.scm,v 14.17 2003/09/30 04:16:45 cph Exp $
+$Id: stream.scm,v 14.18 2003/09/30 04:22:59 cph Exp $
 
 Copyright 1986,1987,1988,1989,1992,1995 Massachusetts Institute of Technology
 Copyright 1998,2003 Massachusetts Institute of Technology
@@ -89,6 +89,20 @@ USA.
              (error:bad-range-argument index 'STREAM-TAIL))
          (loop (force (cdr stream)) (- index 1)))
        stream)))
+
+(define (stream-last-pair stream)
+  (if (not (stream-pair? stream))
+      (if (null? stream)
+         (error:bad-range-argument stream 'STREAM-LAST-PAIR)
+         (error:illegal-stream-element stream 'STREAM-LAST-PAIR 0)))
+  (let loop ((stream stream))
+    (let ((next (force (cdr stream))))
+      (if (stream-pair? next)
+         (loop next)
+         (begin
+           (if (not (null? stream))
+               (error:illegal-stream-element stream 'STREAM-LAST-PAIR 0))
+           stream)))))
 \f
 (define (stream-map procedure stream . streams)
   (cond ((pair? streams)