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<!-- Common Lisp HyperSpec (TM), version 7.0 generated by Kent M. Pitman on Mon, 11-Apr-2005 2:31am EDT -->
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<TITLE>CLHS: Issue WITH-OPEN-FILE-SETQ Writeup</TITLE>
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<H2>Issue WITH-OPEN-FILE-SETQ Writeup</H2>
<PRE><B>Issue:</B> <A HREF="iss362.htm">WITH-OPEN-FILE-SETQ</A><P>
<B>References:</B> <A REL=DEFINITION HREF="../Body/m_w_open.htm#with-open-file"><B>WITH-OPEN-FILE</B></A><P>
<A REL=DEFINITION HREF="../Body/m_w_op_1.htm#with-open-stream"><B>WITH-OPEN-STREAM</B></A><P>
<A REL=DEFINITION HREF="../Body/m_w_in_f.htm#with-input-from-string"><B>WITH-INPUT-FROM-STRING</B></A><P>
<A REL=DEFINITION HREF="../Body/m_w_out_.htm#with-output-to-string"><B>WITH-OUTPUT-TO-STRING</B></A><P>
Related issues: <A HREF="iss363.htm">WITH-OPEN-FILE-STREAM-EXTENT</A><P>
<B>Category:</B> CLARIFICATION<P>
<B>Edit history:</B> v1, 13 Feb 1991, Sandra Loosemore<P>
v2, 11 Mar 1991, Sandra Loosemore<P>
<P>
<B>Problem description:<P>
</B><P>
It isn't clear whether it is permissible for the variable bound to<P>
a stream by <A REL=DEFINITION HREF="../Body/m_w_open.htm#with-open-file"><B>WITH-OPEN-FILE</B></A>, <A REL=DEFINITION HREF="../Body/m_w_op_1.htm#with-open-stream"><B>WITH-OPEN-STREAM</B></A>, <A REL=DEFINITION HREF="../Body/m_w_in_f.htm#with-input-from-string"><B>WITH-INPUT-FROM-STRING</B></A>,<P>
or <A REL=DEFINITION HREF="../Body/m_w_out_.htm#with-output-to-string"><B>WITH-OUTPUT-TO-STRING</B></A> may be explicitly assigned to within the body.<P>
The expansion of these macros must include some code to close the stream<P>
after executing the body forms. Can this code refer to the stream<P>
using the user-supplied variable, or must it use another &quot;hidden&quot;<P>
variable in case the user-supplied variable has been assigned to in<P>
the body forms?<P>
<P>
<B>Proposal (WITH-OPEN-FILE-SETQ:EXPLICITLY-VAGUE):<P>
</B><P>
Clarify that the consequences of altering the values of the variables <P>
bound to streams by <A REL=DEFINITION HREF="../Body/m_w_op_1.htm#with-open-stream"><B>WITH-OPEN-STREAM</B></A>, WITH-INPUT-FROM-STREAM,<P>
WITH-OUTPUT-TO-STREAM, and <A REL=DEFINITION HREF="../Body/m_w_open.htm#with-open-file"><B>WITH-OPEN-FILE</B></A> (by using <A REL=DEFINITION HREF="../Body/s_setq.htm#setq"><B>SETQ</B></A>, for example)<P>
are undefined. A Common Lisp compiler may choose to issue a warning<P>
if such a variable appears in a <A REL=DEFINITION HREF="../Body/s_setq.htm#setq"><B>SETQ</B></A>.<P>
<P>
<B>Rationale:<P>
</B><P>
This is consistent with what CLtL says about altering the value of<P>
the counter variable in a <A REL=DEFINITION HREF="../Body/m_dotime.htm#dotimes"><B>DOTIMES</B></A> form.<P>
<P>
<B>Current Practice:<P>
</B><P>
Lucid CL, Allegro CL, the Chestnut Lisp-to-C translator, and Symbolics<P>
Common Lisp all implement <A REL=DEFINITION HREF="../Body/m_w_open.htm#with-open-file"><B>WITH-OPEN-FILE</B></A> in such a way that the <P>
user-supplied variable is referenced to close the stream.<P>
<P>
<B>Cost to Implementors:<P>
</B><P>
None, since this permits implementations to continue to use the<P>
&quot;obvious&quot; expansion.<P>
<P>
<B>Cost to Users:<P>
</B><P>
Probably none. Any user programs that depend on it working the other<P>
way are already clearly not portable.<P>
<P>
<B>Cost of non-adoption:<P>
</B><P>
The language specification will be vague. Users may have portability<P>
problems.<P>
<P>
<B>Performance impact:<P>
</B><P>
Negligible.<P>
<P>
<B>Benefits:<P>
</B><P>
Users will know what to expect and will avoid a portability pitfall.<P>
<P>
<B>Esthetics:<P>
</B><P>
Doesn't look too bad.<P>
<P>
<B>Discussion:<P>
</B><P>
Kent Pitman notes:<P>
<P>
It probably is worth mentioning that the most common abuse of this<P>
situation I've seen is that sometimes users will create broadcast<P>
streams, echo streams, etc., or even implementation-dependent<P>
encapsulations of the indicated stream to the opened file and then set<P>
it back to the indicated variable. (Whether the later call to <A REL=DEFINITION HREF="../Body/f_close.htm#close"><B>CLOSE</B></A><P>
is a good idea to do to the compound stream which results is something<P>
that probably varies from implementation to implementation. This<P>
proposal certainly makes it more clear that users who do this are<P>
living on the edge.)<P>
<P>
Anyway, I just wanted to emphasize that the only scenario was not<P>
something bizarre like someone doing<P>
<P>
(<A REL=DEFINITION HREF="../Body/m_w_open.htm#with-open-file"><B>WITH-OPEN-FILE</B></A> (TEMP ...)<P>
(<A REL=DEFINITION HREF="../Body/f_wr_pr.htm#print"><B>PRINT</B></A> X <A REL=DEFINITION HREF="../Body/t_stream.htm#stream"><B>STREAM</B></A>)<P>
(<A REL=DEFINITION HREF="../Body/s_setq.htm#setq"><B>SETQ</B></A> X (+ 7 2)) ...)<P>
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