Re: multiple values bug in head / call-with-input-file

[Daniel Llorens]

On May 2, 2011, at 19:46, Mark H Weaver wrote:

> Daniel Llorens <address@hidden> writes:
>> scheme@(guile-user)> (call-with-input-string "hello" (lambda (p) (values 1 
>> 2)))
>> $1 = 1
>> $2 = 2
>> 
>> but:
>> 
>> scheme@(guile-user)> (call-with-input-file "hello" (lambda (p) (values 1 2)))
>> $1 = 1
> 
> Indeed this is suboptimal, and probably a bug.
> Thanks for reporting this!
> 
> However, your fix is incorrect.  By using dynamic-wind, your patch
> significantly changes the semantics of call-with-{input,output}-file.

That makes a lot of sense. I copied blindly from with-input..., but of course 
those don't open or close ports. Thanks for the explanation!

Second try follows. I've noticed the same bug in with-x-to/from-file, so I have 
attempted to fix those too, in the way of with-x-to/from-string below.

Regards,

        Daniel

From 014552302aad4a3188c60db2f600c2c229c15cde Mon Sep 17 00:00:00 2001
From: Daniel Llorens <address@hidden>
Date: Mon, 2 May 2011 20:36:33 +0200
Subject: [PATCH] Fix call-with-input-file & relatives for multiple values

* module/ice-9/r4rs.scm (call-with-input-file, call-with-output-file): Rewrite
  with call-with-values.
  (with-input-from-file): use call-with-input-file.
  (with-output-to-file, with-error-to-file): use call-with-output-file.
  Update docstrings to make clear that multiple values may be yielded.
---
 module/ice-9/r4rs.scm |   62 +++++++++++++++++++++++-------------------------
 1 files changed, 30 insertions(+), 32 deletions(-)

diff --git a/module/ice-9/r4rs.scm b/module/ice-9/r4rs.scm
index 4d3feba..f0cc5f6 100644
--- a/module/ice-9/r4rs.scm
+++ b/module/ice-9/r4rs.scm
@@ -140,14 +140,16 @@ already exist. These procedures call PROC
 with one argument: the port obtained by opening the named file for
 input or output.  If the file cannot be opened, an error is
 signalled.  If the procedure returns, then the port is closed
-automatically and the value yielded by the procedure is returned.
+automatically and the value(s) yielded by the procedure is (are) returned.
 If the procedure does not return, then the port will not be closed
 automatically unless it is possible to prove that the port will
 never again be used for a read or write operation."
-  (let* ((file (open-input-file str))
-        (ans (proc file)))
-    (close-input-port file)
-    ans))
+  (let ((p (open-input-file str)))
+    (call-with-values
+      (lambda () (proc p))
+      (lambda vals
+        (close-input-port port)
+        (apply values vals)))))
 
 (define (call-with-output-file str proc)
   "PROC should be a procedure of one argument, and STR should be a
@@ -156,14 +158,16 @@ already exists. These procedures call PROC
 with one argument: the port obtained by opening the named file for
 input or output.  If the file cannot be opened, an error is
 signalled.  If the procedure returns, then the port is closed
-automatically and the value yielded by the procedure is returned.
+automatically and the value(s) yielded by the procedure is (are) returned.
 If the procedure does not return, then the port will not be closed
 automatically unless it is possible to prove that the port will
 never again be used for a read or write operation."
-  (let* ((file (open-output-file str))
-        (ans (proc file)))
-    (close-output-port file)
-    ans))
+  (let ((p (open-output-file str)))
+    (call-with-values
+      (lambda () (proc p))
+      (lambda vals
+        (close-output-port p)
+        (apply values vals)))))
 
 (define (with-input-from-port port thunk)
   (let* ((swaports (lambda () (set! port (set-current-input-port port)))))
@@ -177,50 +181,44 @@ never again be used for a read or write operation."
   (let* ((swaports (lambda () (set! port (set-current-error-port port)))))
     (dynamic-wind swaports thunk swaports)))
 
-(define (with-input-from-file file thunk)
-  "THUNK must be a procedure of no arguments, and FILE must be a
+(define (with-input-from-file str thunk)
+  "THUNK must be a procedure of no arguments, and STR must be a
 string naming a file.  The file must already exist. The file is opened for
 input, an input port connected to it is made
 the default value returned by `current-input-port', 
 and the THUNK is called with no arguments.
 When the THUNK returns, the port is closed and the previous
-default is restored.  Returns the value yielded by THUNK.  If an
+default is restored.  Returns the value(s) yielded by THUNK.  If an
 escape procedure is used to escape from the continuation of these
 procedures, their behavior is implementation dependent."
-  (let* ((nport (open-input-file file))
-        (ans (with-input-from-port nport thunk)))
-    (close-port nport)
-    ans))
+  (call-with-input-file str
+   (lambda (p) (with-input-from-port p thunk))))
 
-(define (with-output-to-file file thunk)
-  "THUNK must be a procedure of no arguments, and FILE must be a
+(define (with-output-to-file str thunk)
+  "THUNK must be a procedure of no arguments, and STR must be a
 string naming a file.  The effect is unspecified if the file already exists. 
 The file is opened for output, an output port connected to it is made
 the default value returned by `current-output-port', 
 and the THUNK is called with no arguments.
 When the THUNK returns, the port is closed and the previous
-default is restored.  Returns the value yielded by THUNK.  If an
+default is restored.  Returns the value(s) yielded by THUNK.  If an
 escape procedure is used to escape from the continuation of these
 procedures, their behavior is implementation dependent."
-  (let* ((nport (open-output-file file))
-        (ans (with-output-to-port nport thunk)))
-    (close-port nport)
-    ans))
+  (call-with-output-file str
+   (lambda (p) (with-output-to-port p thunk))))
 
-(define (with-error-to-file file thunk)
-  "THUNK must be a procedure of no arguments, and FILE must be a
+(define (with-error-to-file str thunk)
+  "THUNK must be a procedure of no arguments, and STR must be a
 string naming a file.  The effect is unspecified if the file already exists. 
 The file is opened for output, an output port connected to it is made
 the default value returned by `current-error-port', 
 and the THUNK is called with no arguments.
 When the THUNK returns, the port is closed and the previous
-default is restored.  Returns the value yielded by THUNK.  If an
+default is restored.  Returns the value(s) yielded by THUNK.  If an
 escape procedure is used to escape from the continuation of these
 procedures, their behavior is implementation dependent."
-  (let* ((nport (open-output-file file))
-        (ans (with-error-to-port nport thunk)))
-    (close-port nport)
-    ans))
+  (call-with-output-file str
+   (lambda (p) (with-error-to-port p thunk))))
 
 (define (with-input-from-string string thunk)
   "THUNK must be a procedure of no arguments.
@@ -228,7 +226,7 @@ The test of STRING  is opened for
 input, an input port connected to it is made, 
 and the THUNK is called with no arguments.
 When the THUNK returns, the port is closed.
-Returns the value yielded by THUNK.  If an
+Returns the value(s) yielded by THUNK.  If an
 escape procedure is used to escape from the continuation of these
 procedures, their behavior is implementation dependent."
   (call-with-input-string string
-- 
1.7.4.4