From: jmarshall <jmarshall@jmarshall-glaptop2.roam.corp.google.com>
Date: Sat, 16 Jan 2016 04:50:27 +0000 (-0800)
Subject: Add STREAM-LAST and STREAM-TRUNCATE.  Fixed a typo.
X-Git-Tag: mit-scheme-pucked-9.2.12~373^2~10
X-Git-Url: https://birchwood-abbey.net/git?a=commitdiff_plain;h=3400af94611839efd710d191f983be6d05df86da;p=mit-scheme.git

Add STREAM-LAST and STREAM-TRUNCATE.  Fixed a typo.
---

diff --git a/src/runtime/runtime.pkg b/src/runtime/runtime.pkg
index 4a9bdf35a..10a558c8c 100644
--- a/src/runtime/runtime.pkg
+++ b/src/runtime/runtime.pkg
@@ -4606,6 +4606,7 @@ USA.
 	  stream-first
 	  stream-for-each
 	  stream-head
+	  stream-last
 	  stream-last-pair
 	  stream-length
 	  stream-map
@@ -4614,6 +4615,7 @@ USA.
 	  stream-ref
 	  stream-rest
 	  stream-tail
+	  stream-truncate
 	  stream-write
 	  tail
 	  the-empty-stream)
diff --git a/src/runtime/stream.scm b/src/runtime/stream.scm
index 31da2be30..6c49ebc35 100644
--- a/src/runtime/stream.scm
+++ b/src/runtime/stream.scm
@@ -90,6 +90,9 @@ USA.
 	  (loop (force (cdr stream)) (- index 1)))
 	stream)))
 
+(define (stream-last stream)
+  (stream-car (stream-last-pair stream)))
+
 (define (stream-last-pair stream)
   (if (not (stream-pair? stream))
       (if (null? stream)
@@ -100,7 +103,7 @@ USA.
       (if (stream-pair? next)
 	  (loop next)
 	  (begin
-	    (if (not (null? stream))
+	    (if (not (null? next))
 		(error:illegal-stream-element stream 'STREAM-LAST-PAIR 0))
 	    stream)))))
 
@@ -223,6 +226,17 @@ USA.
 	    (error:illegal-stream-element stream 'STREAM-FILTER 1))
 	'())))
 
+(define (stream-truncate stream predicate)
+  (if (stream-pair? stream)
+      (if (predicate (head stream))
+	  the-empty-stream
+	  (cons-stream (head stream)
+		       (stream-truncate (tail stream) predicate)))
+      (begin
+	(if (not (null? stream))
+	    (error:illegal-stream-element stream 'STREAM-TRUNCATE 1))
+	'())))
+
 (define (stream-write stream #!optional port)
   (let ((port
 	 (if (default-object? port)