From: Guillermo J. Rozas <edu/mit/csail/zurich/gjr>
Date: Wed, 10 May 1989 08:51:11 +0000 (+0000)
Subject: Fix the definition of head and tail to check for a proper stream.
X-Git-Tag: 20090517-FFI~12080
X-Git-Url: https://birchwood-abbey.net/git?a=commitdiff_plain;h=c4745062add099913b99915b1be1f70e9f5d26a8;p=mit-scheme.git

Fix the definition of head and tail to check for a proper stream.
---

diff --git a/v7/src/runtime/stream.scm b/v7/src/runtime/stream.scm
index 6d2f8600c..dac91c94b 100644
--- a/v7/src/runtime/stream.scm
+++ b/v7/src/runtime/stream.scm
@@ -1,6 +1,6 @@
 #| -*-Scheme-*-
 
-$Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/runtime/stream.scm,v 14.2 1988/12/30 06:43:22 cph Exp $
+$Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/runtime/stream.scm,v 14.3 1989/05/10 08:51:11 jinx Rel $
 
 Copyright (c) 1988 Massachusetts Institute of Technology
 
@@ -115,11 +115,15 @@ MIT in each case. |#
 (define-integrable (empty-stream? stream)
   (stream-null? stream))
 
-(define-integrable (head stream)
-  (stream-car stream))
+(define (head stream)
+  (if (stream-pair? stream)
+      (stream-car stream)
+      (error "head: not a proper stream" stream)))
 
-(define-integrable (tail stream)
-  (stream-cdr stream))
+(define (tail stream)
+  (if (stream-pair? stream)
+      (stream-cdr stream)
+      (error "tail: not a proper stream" stream)))
 
 (define prime-numbers-stream)