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<H2>Issue PRINT-CASE-PRINT-ESCAPE-INTERACTION Writeup</H2>
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<PRE><B>Status:</B> proposal VERTICAL-BAR-RULE-NO-UPCASE passed, Jun 89 X3J13<P>
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<P>
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<B>Issue:</B> <A HREF="iss273.htm">PRINT-CASE-PRINT-ESCAPE-INTERACTION</A><P>
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<B>Forum:</B> Cleanup<P>
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<B>References:</B> <A REL=DEFINITION HREF="../Body/v_pr_esc.htm#STprint-escapeST"><B>*PRINT-ESCAPE*</B></A> (pp370-371), <A REL=DEFINITION HREF="../Body/v_pr_cas.htm#STprint-caseST"><B>*PRINT-CASE*</B></A> (pp372), <A REL=DEFINITION HREF="../Body/f_wr_pr.htm#write"><B>WRITE</B></A><P>
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<B>Category:</B> CLARIFICATION<P>
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<B>Edit history:</B> 26-Jan-89, Version 1 by Pitman<P>
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<P>
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<B>Problem Description:<P>
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</B><P>
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The wording on page 372 of CLtL uses fuzzy terms that make it hard<P>
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to tell if <A REL=DEFINITION HREF="../Body/v_pr_esc.htm#STprint-escapeST"><B>*PRINT-ESCAPE*</B></A> interacts with <A REL=DEFINITION HREF="../Body/v_pr_cas.htm#STprint-caseST"><B>*PRINT-CASE*</B></A>.<P>
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<P>
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Paragraph 1 of the description of <A REL=DEFINITION HREF="../Body/v_pr_cas.htm#STprint-caseST"><B>*PRINT-CASE*</B></A> says "This variable<P>
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controls the case (upper, lower, or mixed) in which to print any<P>
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uppercase characters in the names of symbols when vertical-bar<P>
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syntax is used."<P>
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<P>
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Paragraph 2 begins with the seemingly unambiguous statement "Lowercase<P>
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characters in the internal print name are always printed in lowercase"<P>
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but then goes on to muddy the water by saying "and are preceded by<P>
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a single escape character or enclosed by multiple escape characters".<P>
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This escaping presumably only happens in <A REL=DEFINITION HREF="../Body/v_pr_esc.htm#STprint-escapeST"><B>*PRINT-ESCAPE*</B></A> T mode, which<P>
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leads one to wonder if other parts of the <A REL=DEFINITION HREF="../Body/v_pr_esc.htm#STprint-escapeST"><B>*PRINT-ESCAPE*</B></A> description are<P>
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implicitly controlled by <A REL=DEFINITION HREF="../Body/v_pr_esc.htm#STprint-escapeST"><B>*PRINT-ESCAPE*</B></A> as well.<P>
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<P>
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The function <A REL=DEFINITION HREF="../Body/f_wr_pr.htm#write"><B>WRITE</B></A> is affected by implication.<P>
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<P>
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<B>Proposal (PRINT-CASE-PRINT-ESCAPE-INTERACTION:LIKE-PRIN1):<P>
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</B><P>
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Define that <A REL=DEFINITION HREF="../Body/v_pr_cas.htm#STprint-caseST"><B>*PRINT-CASE*</B></A> cases characters the same as <A REL=DEFINITION HREF="../Body/f_wr_pr.htm#prin1"><B>PRIN1</B></A> would.<P>
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<P>
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<B>Proposal (PRINT-CASE-PRINT-ESCAPE-INTERACTION:LIKE-WRITE-STRING):<P>
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</B><P>
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Define that <A REL=DEFINITION HREF="../Body/v_pr_cas.htm#STprint-caseST"><B>*PRINT-CASE*</B></A> has an effect only when <A REL=DEFINITION HREF="../Body/v_pr_esc.htm#STprint-escapeST"><B>*PRINT-ESCAPE*</B></A> is T.<P>
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When <A REL=DEFINITION HREF="../Body/v_pr_cas.htm#STprint-caseST"><B>*PRINT-CASE*</B></A> is <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A>, <A REL=DEFINITION HREF="../Body/f_wr_stg.htm#write-string"><B>WRITE-STRING</B></A> is used directly.<P>
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<P>
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<B>Proposal (PRINT-CASE-PRINT-ESCAPE-INTERACTION:VERTICAL-BAR-RULE-NO-UPCASE):<P>
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</B><P>
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Define that <A REL=DEFINITION HREF="../Body/v_pr_cas.htm#STprint-caseST"><B>*PRINT-CASE*</B></A> has an effect at all times when <A REL=DEFINITION HREF="../Body/v_pr_esc.htm#STprint-escapeST"><B>*PRINT-ESCAPE*</B></A><P>
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is <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A>. Define that <A REL=DEFINITION HREF="../Body/v_pr_cas.htm#STprint-caseST"><B>*PRINT-CASE*</B></A> also has an effect when <A REL=DEFINITION HREF="../Body/v_pr_esc.htm#STprint-escapeST"><B>*PRINT-ESCAPE*</B></A><P>
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is T unless inside an escape context (i.e., unless between vertical bars<P>
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or after a slash). Under no circumstance is any character which was <P>
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lowercase in the internal representation ever presented as uppercase<P>
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due to <A REL=DEFINITION HREF="../Body/v_pr_cas.htm#STprint-caseST"><B>*PRINT-CASE*</B></A>.<P>
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<P>
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<B>Proposal (PRINT-CASE-PRINT-ESCAPE-INTERACTION:VERTICAL-BAR-RULE-PERMIT-UPCASE):<P>
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</B><P>
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Like VERTICAL-BAR-RULE-NO-UPCASE, but permit <A REL=DEFINITION HREF="../Body/v_pr_cas.htm#STprint-caseST"><B>*PRINT-CASE*</B></A> to upcase<P>
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lowercase characters in the <A REL=DEFINITION HREF="../Body/v_pr_esc.htm#STprint-escapeST"><B>*PRINT-ESCAPE*</B></A> <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A> case since preservation of<P>
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Lisp syntax is not important there.<P>
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<P>
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<B>Proposal (PRINT-CASE-PRINT-ESCAPE-INTERACTION:EXPLICITLY-VAGUE):<P>
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</B><P>
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Specify that the effect of <A REL=DEFINITION HREF="../Body/v_pr_cas.htm#STprint-caseST"><B>*PRINT-CASE*</B></A> when <A REL=DEFINITION HREF="../Body/v_pr_esc.htm#STprint-escapeST"><B>*PRINT-ESCAPE*</B></A> is <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A><P>
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is implementation-dependent.<P>
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<P>
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<B>Test Case:<P>
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</B><P>
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(<A REL=DEFINITION HREF="../Body/s_let_l.htm#let"><B>LET</B></A> ((RESULT '()) (TABWIDTH 12))<P>
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(<A REL=DEFINITION HREF="../Body/m_dolist.htm#dolist"><B>DOLIST</B></A> (<A REL=DEFINITION HREF="../Body/t_symbol.htm#symbol"><B>SYMBOL</B></A> '(|x| |FoObAr| |fOo|))<P>
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(<A REL=DEFINITION HREF="../Body/s_let_l.htm#let"><B>LET</B></A> ((TAB -1))<P>
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(<A REL=DEFINITION HREF="../Body/f_format.htm#format"><B>FORMAT</B></A> T "~&")<P>
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(<A REL=DEFINITION HREF="../Body/m_dolist.htm#dolist"><B>DOLIST</B></A> (ESCAPE '(T <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A>))<P>
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(<A REL=DEFINITION HREF="../Body/m_dolist.htm#dolist"><B>DOLIST</B></A> (<A REL=DEFINITION HREF="../Body/m_case_.htm#case"><B>CASE</B></A> '(:UPCASE :DOWNCASE :CAPITALIZE))<P>
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(<A REL=DEFINITION HREF="../Body/f_format.htm#format"><B>FORMAT</B></A> T "~VT" (* (<A REL=DEFINITION HREF="../Body/m_incf_.htm#incf"><B>INCF</B></A> TAB) TABWIDTH))<P>
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(<A REL=DEFINITION HREF="../Body/f_wr_pr.htm#write"><B>WRITE</B></A> <A REL=DEFINITION HREF="../Body/t_symbol.htm#symbol"><B>SYMBOL</B></A> :ESCAPE ESCAPE :CASE <A REL=DEFINITION HREF="../Body/m_case_.htm#case"><B>CASE</B></A>))))))<P>
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<P>
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For each of the following, two clusters of output is shown. The first is<P>
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how an implementation which leans heavily on vertical bars might work.<P>
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The second is how an implementation which leans heavily on slash might<P>
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work. In fact, other interpretations are possible (mixing slash and <P>
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vertical bar). These examples are not an exhaustive analysis of the <P>
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implications of each proposal.<P>
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<P>
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Possible outputs under LIKE-PRIN1:<P>
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<P>
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|x| |x| |x| x x x<P>
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|FoObAr| |FoObAr| |FoObAr| FoObAr FoObAr FoObAr<P>
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|fOo| |fOo| |fOo| fOo fOo fOo<P>
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<P>
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\x \x \x x x x<P>
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F\oO\bA\r f\oo\ba\r F\oo\ba\r FoObAr foobar Foobar <P>
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\fO\o \fo\o \fo\o fOo foo foo<P>
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<P>
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Possible output under LIKE-WRITE-STRING:<P>
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<P>
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|x| |x| |x| x x x<P>
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|FoObAr| |FoObAr| |FoObAr| FoObAr FoObAr FoObAr<P>
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|fOo| |fOo| |fOo| fOo fOo fOo<P>
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<P>
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\x \x \x x x x<P>
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F\oO\bA\r f\oo\ba\r F\oo\ba\r FoObAr FoObAr FoObAr<P>
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\fO\o \fo\o \fo\o fOo fOo fOo<P>
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<P>
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Possible output under VERTICAL-BAR-RULE-NO-UPCASE:<P>
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<P>
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|x| |x| |x| x x x<P>
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|FoObAr| |FoObAr| |FoObAr| FoObAr foobar Foobar<P>
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|fOo| |fOo| |fOo| fOo foo foo<P>
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<P>
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\x \x \x x x x<P>
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F\oO\bA\r f\oo\ba\r F\oo\ba\r FoObAr foobar Foobar<P>
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\fO\o \fo\o \fo\o fOo foo foo<P>
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<P>
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Possible output under VERTICAL-BAR-RULE-PERMIT-UPCASE:<P>
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<P>
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|x| |x| |x| X x X<P>
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|FoObAr| |FoObAr| |FoObAr| FOOBAR foobar Foobar<P>
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|fOo| |fOo| |fOo| FOO foo Foo<P>
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<P>
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\x \x \x X x X<P>
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F\oO\bA\r f\oo\ba\r F\oo\ba\r FOOBAR foobar Foobar<P>
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\fO\o \fO\o \fO\o FOO foo Foo<P>
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<P>
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<B>Rationale:<P>
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</B><P>
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It's silly for implementations to vary on this point.<P>
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<P>
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<B>Current Practice:<P>
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</B><P>
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A strict reading of CLtL suggests that probably VERTICAL-BAR-RULE-NO-UPCASE<P>
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is the most correct. <P>
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<P>
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Symbolics Genera doesn't do any of these. It was trying to do <P>
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VERTICAL-BAR-NO-UPCASE, but it had a bug which was about to be fixed when<P>
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this issue was raised.<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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Probably trivial.<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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Negligible in most cases. Probably very few users depend on this.<P>
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Those who do depend on it probably do so because they think the<P>
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behavior doesn't vary and probably don't get the portable behavior they<P>
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expect.<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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Gratuitous variation between implementations.<P>
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<P>
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<B>Benefits:<P>
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</B><P>
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Cost of non-adoption is avoided.<P>
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<P>
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<B>Aesthetics:<P>
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</B><P>
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Anything that makes the language tighter probably improves aesthetics.<P>
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<P>
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Only VERTICAL-BAR-RULE-PERMIT-UPCASE and LIKE-WRITE-STRING have really<P>
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useful behaviors in the :ESCAPE <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A> situation. Of these, perhaps only<P>
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VERTICAL-BAR-RULE-PERMIT-UPCASE is really visually pleasant.<P>
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<P>
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<B>Discussion:<P>
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</B><P>
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Pitman doesn't think the particular choice is very important. He just<P>
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wants the issue to be resolved. His slight preference is for<P>
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VERTICAL-BAR-RULE-PERMIT-UPCASE, then LIKE-WRITE-STRING, then either<P>
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of LIKE-PRIN1 or VERTICAL-BAR-RULE-NO-UPCASE. He sees no reason to go<P>
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with EXPLICITLY-VAGUE unless we deadlock.<P>
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<P>
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Michael Greenwald, who raised the issue at Symbolics, doesn't have<P>
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a preference either but believes that CLtL (perhaps unintentionally)<P>
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leans toward VERTICAL-BAR-RULE-NO-UPCASE.<P>
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<P>
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-----<P>
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Additional Discussion from CL-Cleanup:<P>
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<P>
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David Gray responds:<P>
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> Possible output under VERTICAL-BAR-RULE-NO-UPCASE:<P>
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> <P>
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> |x| |x| |x| x x x<P>
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> |FoObAr| |FoObAr| |FoObAr| FoObAr foobar Foobar<P>
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> |fOo| |fOo| |fOo| fOo foo foo<P>
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This is exactly what the Explorer does.<P>
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<P>
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There are several options for this issue, but if you're looking for one<P>
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to focus on, VERTICAL-BAR-RULE-NO-UPCASE is probably the one we'll push<P>
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if this issue comes up for discussion since it is believed most compatible<P>
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with current practice.<P>
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-kmp<P>
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<P>
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</PRE>
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