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<H1><A REV=MADE HREF="http://www.lispworks.com/"><IMG WIDTH=80 HEIGHT=65 ALT="[LISPWORKS]" SRC="../Graphics/LWSmall.gif" ALIGN=Bottom></A><A REL=TOP HREF="../Front/index.htm"><IMG WIDTH=237 HEIGHT=65 ALT="[Common Lisp HyperSpec (TM)]" SRC="../Graphics/CLHS_Sm.gif" ALIGN=Bottom></A> <A REL=PREV HREF="../Issues/iss322_w.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="../Issues/iss323.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="../Issues/iss324_w.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<H2>Issue STANDARD-INPUT-INITIAL-BINDING Writeup</H2>
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<PRE><B>Status:</B> Passed, Jan 89 X3J13<P>
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<B>Issue:</B> <A HREF="iss323.htm">STANDARD-INPUT-INITIAL-BINDING</A><P>
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<B>References:</B> Standard streams (pp. 327-329)<P>
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<B>Category:</B> CHANGE<P>
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<B>Edit history:</B> Version 1 by Pierson and Haflich 1/19/87<P>
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Version 2 by Pierson 2/29/88<P>
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Version 3 by Pierson 5/23/88, per comments by Moon<P>
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Version 4 by Pierson 5/26/88, clean up<P>
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Version 5 by Pierson 6/28/88, simple design per Masinter<P>
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Version 6 by Pierson 7/ 5/88, clean up and split issue<P>
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Version 7 by Pierson 7/ 8/88, clean up per Pitman<P>
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Version 8 by Pierson 7/ 8/88, yet more clean up<P>
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<P>
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<B>Problem description:<P>
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</B><P>
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CLtL requires that <A REL=DEFINITION HREF="../Body/v_debug_.htm#STstandard-inputST"><B>*STANDARD-INPUT*</B></A>, <A REL=DEFINITION HREF="../Body/v_debug_.htm#STstandard-outputST"><B>*STANDARD-OUTPUT*</B></A>,<P>
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<A REL=DEFINITION HREF="../Body/v_debug_.htm#STerror-outputST"><B>*ERROR-OUTPUT*</B></A>, <A REL=DEFINITION HREF="../Body/v_debug_.htm#STtrace-outputST"><B>*TRACE-OUTPUT*</B></A>, <A REL=DEFINITION HREF="../Body/v_debug_.htm#STquery-ioST"><B>*QUERY-IO*</B></A>, and <A REL=DEFINITION HREF="../Body/v_debug_.htm#STdebug-ioST"><B>*DEBUG-IO*</B></A> are<P>
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initially bound to synonym streams to <A REL=DEFINITION HREF="../Body/v_termin.htm#STterminal-ioST"><B>*TERMINAL-IO*</B></A>. This requirement<P>
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hampers the integration of Common Lisp with many existing and<P>
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potential operating environments.<P>
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<P>
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For example, a Unix implementation is currently unable to legally<P>
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support Unix <A REL=DEFINITION HREF="../Body/07_ffb.htm#standard"><B>standard</B></A> error output even though Common Lisp defines<P>
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<A REL=DEFINITION HREF="../Body/v_debug_.htm#STerror-outputST"><B>*ERROR-OUTPUT*</B></A> because <A REL=DEFINITION HREF="../Body/v_debug_.htm#STerror-outputST"><B>*ERROR-OUTPUT*</B></A> is required to start out bound<P>
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to the same stream as <A REL=DEFINITION HREF="../Body/v_debug_.htm#STstandard-outputST"><B>*STANDARD-OUTPUT*</B></A>. A workstation environnment<P>
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which provides stream access to windows as an extension is currently<P>
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forbidden to make <A REL=DEFINITION HREF="../Body/m_tracec.htm#trace"><B>trace</B></A> output appear in a separate window by default<P>
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because <A REL=DEFINITION HREF="../Body/v_debug_.htm#STtrace-outputST"><B>*TRACE-OUTPUT*</B></A> is required to start out bound to the same<P>
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stream as <A REL=DEFINITION HREF="../Body/v_debug_.htm#STstandard-outputST"><B>*STANDARD-OUTPUT*</B></A>.<P>
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<P>
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<B>Proposal (STANDARD-INPUT-INITIAL-BINDING:DEFINED-CONTRACTS):<P>
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</B><P>
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A Common Lisp implementation is required to <A REL=DEFINITION HREF="../Body/f_provid.htm#provide"><B>provide</B></A> the following<P>
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initial streams. Each initial stream has a specific purpose as<P>
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defined in CLtL. This proposal redefines the initial bindings of<P>
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the streams and leaves the rest of the CLtL description unchanged.<P>
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<P>
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<A REL=DEFINITION HREF="../Body/v_termin.htm#STterminal-ioST"><B>*TERMINAL-IO*</B></A><P>
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<A REL=DEFINITION HREF="../Body/v_debug_.htm#STstandard-inputST"><B>*STANDARD-INPUT*</B></A><P>
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<A REL=DEFINITION HREF="../Body/v_debug_.htm#STstandard-outputST"><B>*STANDARD-OUTPUT*</B></A><P>
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<A REL=DEFINITION HREF="../Body/v_debug_.htm#STerror-outputST"><B>*ERROR-OUTPUT*</B></A><P>
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<A REL=DEFINITION HREF="../Body/v_debug_.htm#STtrace-outputST"><B>*TRACE-OUTPUT*</B></A><P>
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<A REL=DEFINITION HREF="../Body/v_debug_.htm#STquery-ioST"><B>*QUERY-IO*</B></A><P>
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<A REL=DEFINITION HREF="../Body/v_debug_.htm#STdebug-ioST"><B>*DEBUG-IO*</B></A><P>
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<P>
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The initial bindings of these variables are undefined except<P>
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that:<P>
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1. They are all initially bound to open streams.<P>
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2. The streams must support input and/or output as<P>
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indicated by the variable name.<P>
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3. None of the <A REL=DEFINITION HREF="../Body/07_ffb.htm#standard"><B>standard</B></A> streams (including <A REL=DEFINITION HREF="../Body/v_termin.htm#STterminal-ioST"><B>*TERMINAL-IO*</B></A>)<P>
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may be directed by synonym streams to another of these<P>
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stream variables (except <A REL=DEFINITION HREF="../Body/v_termin.htm#STterminal-ioST"><B>*TERMINAL-IO*</B></A>), whether<P>
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directly or by indirection via some composite stream<P>
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such as a two way stream with one of the arms being a<P>
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synonym stream.<P>
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4. Any or all of these streams may be synonyms for the<P>
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common implementation dependent stream. For example,<P>
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in an interactive Common Lisp invocation running on a<P>
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character terminal, all of the streams mentioned here<P>
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might be synonym streams (or two-way streams to synonym<P>
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streams) to a pair of hidden terminal input/output<P>
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streams maintained by the implementation.<P>
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<P>
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The intent of the above rules is to ensure that it is always<P>
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safe to bind any of the above variables to another of the<P>
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above variables without unduly restricting implementation<P>
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flexibility.<P>
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<P>
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<P>
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<B>Examples:<P>
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</B><P>
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(<A REL=DEFINITION HREF="../Body/s_progn.htm#progn"><B>PROGN</B></A><P>
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(<A REL=DEFINITION HREF="../Body/f_wr_pr.htm#print"><B>PRINT</B></A> "Output" <A REL=DEFINITION HREF="../Body/v_debug_.htm#STstandard-outputST"><B>*STANDARD-OUTPUT*</B></A>)<P>
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(<A REL=DEFINITION HREF="../Body/f_wr_pr.htm#print"><B>PRINT</B></A> "Error" <A REL=DEFINITION HREF="../Body/v_debug_.htm#STerror-outputST"><B>*ERROR-OUTPUT*</B></A>))<P>
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<P>
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In current Common Lisp will write:<P>
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------<P>
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Output<P>
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Error<P>
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------<P>
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<P>
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With proposal *might* write:<P>
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------<P>
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Output<P>
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------<P>
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and "Error" appears somewhere else.<P>
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<P>
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<P>
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(<A REL=DEFINITION HREF="../Body/s_let_l.htm#let"><B>LET</B></A> ((<A REL=DEFINITION HREF="../Body/v_debug_.htm#STstandard-outputST"><B>*STANDARD-OUTPUT*</B></A> <A REL=DEFINITION HREF="../Body/v_debug_.htm#STdebug-ioST"><B>*DEBUG-IO*</B></A>))<P>
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...)<P>
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<P>
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In current Common Lisp: <P>
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Might cause a circular stream reference if <A REL=DEFINITION HREF="../Body/v_debug_.htm#STdebug-ioST"><B>*DEBUG-IO*</B></A> was<P>
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bound to a two-way stream made up of synonym streams to<P>
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<A REL=DEFINITION HREF="../Body/v_debug_.htm#STstandard-inputST"><B>*STANDARD-INPUT*</B></A> and <A REL=DEFINITION HREF="../Body/v_debug_.htm#STstandard-outputST"><B>*STANDARD-OUTPUT*</B></A>.<P>
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<P>
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With this proposal:<P>
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Would be guaranteed not to cause a circular stream reference<P>
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unless the initial value of <A REL=DEFINITION HREF="../Body/v_debug_.htm#STdebug-ioST"><B>*DEBUG-IO*</B></A> had been changed to a value<P>
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that did not conform the restrictions in this proposal. While no<P>
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Common Lisp implementation should do this, a user program might.<P>
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<P>
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<P>
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(<A REL=DEFINITION HREF="../Body/s_let_l.htm#let"><B>LET</B></A> ((<A REL=DEFINITION HREF="../Body/v_debug_.htm#STstandard-inputST"><B>*STANDARD-INPUT*</B></A> <A REL=DEFINITION HREF="../Body/v_termin.htm#STterminal-ioST"><B>*TERMINAL-IO*</B></A>)<P>
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(<A REL=DEFINITION HREF="../Body/v_debug_.htm#STstandard-outputST"><B>*STANDARD-OUTPUT*</B></A> <A REL=DEFINITION HREF="../Body/v_termin.htm#STterminal-ioST"><B>*TERMINAL-IO*</B></A>))<P>
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...)<P>
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<P>
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In current Common Lisp: <P>
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Might cause a circular stream reference because <A REL=DEFINITION HREF="../Body/v_termin.htm#STterminal-ioST"><B>*TERMINAL-IO*</B></A> was<P>
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bound to a two-way stream made up of synonym streams to<P>
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<A REL=DEFINITION HREF="../Body/v_debug_.htm#STstandard-inputST"><B>*STANDARD-INPUT*</B></A> and <A REL=DEFINITION HREF="../Body/v_debug_.htm#STstandard-outputST"><B>*STANDARD-OUTPUT*</B></A>.<P>
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<P>
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With this proposal:<P>
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Would be guaranteed not to cause a circular stream reference.<P>
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<P>
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<P>
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<B>Rationale:<P>
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</B><P>
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This proposal attempts to <A REL=DEFINITION HREF="../Body/f_provid.htm#provide"><B>provide</B></A> a balance between over-specifying<P>
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behavior to the point that Lisp programs can't behave like other<P>
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programs in conventional operating systems and providing enough<P>
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specification that Common Lisp programs can perform portable input and<P>
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output.<P>
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<P>
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<B>Current practice:<P>
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</B><P>
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Lucid binds <A REL=DEFINITION HREF="../Body/v_termin.htm#STterminal-ioST"><B>*TERMINAL-IO*</B></A> to a special internal stream type. Franz<P>
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binds <A REL=DEFINITION HREF="../Body/v_termin.htm#STterminal-ioST"><B>*TERMINAL-IO*</B></A> to a special internal stream type for terminal<P>
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streams which reads from Unix <A REL=DEFINITION HREF="../Body/07_ffb.htm#standard"><B>standard</B></A> input and writes to Unix<P>
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<A REL=DEFINITION HREF="../Body/07_ffb.htm#standard"><B>standard</B></A> output. KCL binds <A REL=DEFINITION HREF="../Body/v_termin.htm#STterminal-ioST"><B>*TERMINAL-IO*</B></A> to a <A REL=DEFINITION HREF="../Body/07_ffb.htm#standard"><B>standard</B></A> <A REL=DEFINITION HREF="../Body/t_two_wa.htm#two-way-stream"><B>two-way-stream</B></A><P>
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with input from Unix <A REL=DEFINITION HREF="../Body/07_ffb.htm#standard"><B>standard</B></A> input and output to Unix <A REL=DEFINITION HREF="../Body/07_ffb.htm#standard"><B>standard</B></A><P>
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output. Symbolics Genera binds <A REL=DEFINITION HREF="../Body/v_termin.htm#STterminal-ioST"><B>*TERMINAL-IO*</B></A> as appropriate for each<P>
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process, usually to a window for interactive applications or to a<P>
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stream which will conjure an interaction window on demand for<P>
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background tasks.<P>
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<P>
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<B>Cost to Implementors:<P>
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</B><P>
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All implementations will have to change to some degree but the changes<P>
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will probably be simple and localized. All known implementations<P>
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already support the underlying streams required to implement this<P>
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proposal.<P>
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<P>
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<B>Cost to Users:<P>
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</B><P>
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User code which depends on the strict binding hierarchy in CLtL may<P>
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have to change. <P>
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<P>
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<B>Cost of non-Adoption:<P>
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</B><P>
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It will continue to be difficult or impossible to integrate portable<P>
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Common Lisp progams in conventional operating system environments.<P>
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Many implementations will have to continue to choose between<P>
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conforming to the <A REL=DEFINITION HREF="../Body/07_ffb.htm#standard"><B>standard</B></A> and providing a superior user environment.<P>
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<P>
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<B>Benefits:<P>
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</B><P>
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Implementations will be more able to match their IO behavior to their<P>
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environment and their user's expectations.<P>
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<P>
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<B>Aesthetics:<P>
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</B><P>
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Improved because this area becomes better defined.<P>
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<P>
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<B>Discussion:<P>
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</B><P>
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Moon says that <A REL=DEFINITION HREF="../Body/v_termin.htm#STterminal-ioST"><B>*TERMINAL-IO*</B></A> (and, by extension, <A REL=DEFINITION HREF="../Body/v_debug_.htm#STquery-ioST"><B>*QUERY-IO*</B></A>, and<P>
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<A REL=DEFINITION HREF="../Body/v_debug_.htm#STdebug-ioST"><B>*DEBUG-IO*</B></A>) should fail to work in a non-interactive environment where<P>
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nothing like a terminal exists. This proposal fails to address this.<P>
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<P>
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Masinter notes that:<P>
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``In many multi-processing multi-window environments,<P>
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the "initial binding" for <A REL=DEFINITION HREF="../Body/v_debug_.htm#STstandard-inputST"><B>*STANDARD-INPUT*</B></A>, *QUERY-INPUT*<P>
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differs for each process.'' <P>
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<P>
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Pierson and Pitman support <A HREF="iss323.htm">STANDARD-INPUT-INITIAL-BINDING:DEFINED-CONTRACTS</A>.<P>
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</PRE>
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