From d731f92e7da45f66a2c79950cfe6c22159eb7e35 Mon Sep 17 00:00:00 2001
From: Vasilij Schneidermann <mail@vasilij.de>
Date: Thu, 7 Sep 2017 17:07:05 +0200
Subject: [PATCH] read-string: return EOF if nothing can be read

R7RS states that there's three possible scenarios for read-string:

- More characters can be read than asked for (return string)
- Less characters can be read than asked for (return string)
- No characters can be read (return EOF)

This commit ensures the last scenario works as intended.
---
 scheme/base.sld | 32 +++++++++++++++++---------------
 1 file changed, 17 insertions(+), 15 deletions(-)

diff --git a/scheme/base.sld b/scheme/base.sld
index 47af273b..8dcbbfb9 100644
--- a/scheme/base.sld
+++ b/scheme/base.sld
@@ -645,21 +645,23 @@
       (let ((port (if (null? opts)
                       (current-input-port)
                       (car opts))))
-        (let loop ((acc '())
-                   (i k)
-                   (chr #f))
-          (cond
-            ((eof-object? chr)
-             (list->string 
-               (reverse acc)))
-            ((zero? i)
-             (list->string 
-               (reverse 
-                 (if chr (cons chr acc) acc))))
-            (else
-             (loop (if chr (cons chr acc) acc)
-                   (- i 1)
-                   (read-char port)))))))
+        (if (eof-object? (peek-char port))
+            (eof-object)
+            (let loop ((acc '())
+                       (i k)
+                       (chr #f))
+              (cond
+               ((eof-object? chr)
+                (list->string
+                 (reverse acc)))
+               ((zero? i)
+                (list->string
+                 (reverse
+                  (if chr (cons chr acc) acc))))
+               (else
+                (loop (if chr (cons chr acc) acc)
+                      (- i 1)
+                      (read-char port))))))))
     (define (flush-output-port . port)
       (if (null? port)
         (Cyc-flush-output-port (current-output-port))