113 lines
6.4 KiB
HTML
113 lines
6.4 KiB
HTML
<!-- Common Lisp HyperSpec (TM), version 7.0 generated by Kent M. Pitman on Mon, 11-Apr-2005 2:31am EDT -->
|
|
<HTML>
|
|
<HEAD>
|
|
<TITLE>CLHS: Issue FORMAT-COMMA-INTERVAL Writeup</TITLE>
|
|
<LINK HREF="../Data/clhs.css" REL="stylesheet" TYPE="text/css" />
|
|
<META HTTP-EQUIV="Author" CONTENT="Kent M. Pitman">
|
|
<META HTTP-EQUIV="Organization" CONTENT="LispWorks Ltd.">
|
|
<LINK REL=TOP HREF="../Front/index.htm">
|
|
<LINK REL=COPYRIGHT HREF="../Front/Help.htm#Legal">
|
|
<LINK REL=DISCLAIMER HREF="../Front/Help.htm#Disclaimer">
|
|
<LINK REL=PREV HREF="../Issues/iss165_w.htm">
|
|
<LINK REL=UP HREF="../Issues/iss166.htm">
|
|
<LINK REL=NEXT HREF="../Issues/iss167_w.htm">
|
|
</HEAD>
|
|
<BODY>
|
|
<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/iss165_w.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="../Issues/iss166.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="../Issues/iss167_w.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
|
|
|
|
<HR>
|
|
|
|
|
|
|
|
<H2>Issue FORMAT-COMMA-INTERVAL Writeup</H2>
|
|
|
|
<PRE><B>Issue:</B> <A HREF="iss166.htm">FORMAT-COMMA-INTERVAL</A><P>
|
|
<B>References:</B> <A REL=DEFINITION HREF="../Body/f_format.htm#format"><B>FORMAT</B></A> integer printing (p. 388-9)<P>
|
|
<B>Category:</B> ADDITION<P>
|
|
<B>Edit history:</B> Version 1, Pavel, 10-Jun-87<P>
|
|
Version 2, Masinter, 15-Jun-87<P>
|
|
<P>
|
|
<B>Problem description: <P>
|
|
</B><P>
|
|
There are times when users would like to print out numbers with some punctuation<P>
|
|
between groups of digits. The "commachar" argument to the ~D, ~B, ~O, ~X, and<P>
|
|
~R <A REL=DEFINITION HREF="../Body/f_format.htm#format"><B>FORMAT</B></A> directives was introduced to fill that need. Unfortunately, the<P>
|
|
interval at which the commachar should be printed is always every three digits.<P>
|
|
This constraint is annoying when a different interval would be more appropriate.<P>
|
|
<P>
|
|
<B>Proposal (FORMAT-COMMA-INTERVAL:YES):<P>
|
|
</B><P>
|
|
Add a fourth argument to the ~D, ~B, ~X, and ~O <A REL=DEFINITION HREF="../Body/f_format.htm#format"><B>FORMAT</B></A> directives, and a fifth<P>
|
|
argument to the ~R directive, to be called the "comma-interval". This value<P>
|
|
must be an integer and defaults to 3. When the : modifier is given to any of<P>
|
|
these directives, the "commachar" is printed between groups of "comma-interval"<P>
|
|
digits.<P>
|
|
<P>
|
|
<B>Test Cases:<P>
|
|
</B><P>
|
|
Under the proposal, the following forms return the indicated values:<P>
|
|
(format nil "~,,' ,4:B" 13) => "1101"<P>
|
|
(format nil "~,,' ,4:B" 17) => "1 0001"<P>
|
|
(format nil "~19,0,' ,4:B" 3333) => "0000 1101 0000 0101"<P>
|
|
(format nil "~3,,,' ,2:R" 17) => "1 22"<P>
|
|
(format nil "~,,'|,2:D" #xFFFF) => "6|55|35"<P>
|
|
<P>
|
|
<B>Rationale: <P>
|
|
</B><P>
|
|
The current specification of <A REL=DEFINITION HREF="../Body/f_format.htm#format"><B>FORMAT</B></A> gives the user control over almost all of<P>
|
|
the facets of printing integers. Only the wired-in constant for the<P>
|
|
comma-interval remains, even though there are uses for varying that number. For<P>
|
|
example, in many contexts, it would be convenient to be able to print out<P>
|
|
numbers in binary with a space between each group of four bits. <A REL=DEFINITION HREF="../Body/f_format.htm#format"><B>FORMAT</B></A> does not<P>
|
|
currently allow specification of the commachar printing interval so users<P>
|
|
needing this functionality must write it themselves, duplicating much of the<P>
|
|
logic in every implementation's integer printing code. Other uses, requiring<P>
|
|
other intervals, can be imagined. For example, using a "commachar" of #\Newline<P>
|
|
and a "comma-interval" of, say, 72, very large bignums could be printed in such<P>
|
|
a way as to ensure line-breaks at appropriate places.<P>
|
|
<P>
|
|
<B>Current practice:<P>
|
|
</B><P>
|
|
No released implementations currently support this feature.<P>
|
|
<P>
|
|
<B>Cost to implementors: <P>
|
|
</B><P>
|
|
The change in the implementation of <A REL=DEFINITION HREF="../Body/f_format.htm#format"><B>FORMAT</B></A> is reasonably minor and, in most<P>
|
|
cases, highly localized. Usually, the change is as simple as taking an extra<P>
|
|
parameter and using it instead of a wired-in value of 3.<P>
|
|
<P>
|
|
<B>Cost to users:<P>
|
|
</B><P>
|
|
Since the proposal involves the addition of an argument to certain directives,<P>
|
|
the change would be entirely upward-compatible. No user code would need to be<P>
|
|
converted.<P>
|
|
<P>
|
|
<B>Cost of non-adoption: <P>
|
|
</B><P>
|
|
Users desiring this functionality will have to write it themselves, duplicating<P>
|
|
much of the logic involved in printing integers at all.<P>
|
|
<P>
|
|
<B>Benefits: <P>
|
|
</B><P>
|
|
One of the few remaining inflexibilities in integer printing is eliminated with<P>
|
|
a net increase in user-visible functionality.<P>
|
|
<P>
|
|
<B>Esthetics: <P>
|
|
</B><P>
|
|
By parameterizing one of the final pieces of wired-in behavior from integer<P>
|
|
printing, this small part of the workings of <A REL=DEFINITION HREF="../Body/f_format.htm#format"><B>FORMAT</B></A> would be perceived as having<P>
|
|
been cleaned up.<P>
|
|
<P>
|
|
<B>Discussion: <P>
|
|
</B><P>
|
|
Several members of the cleanup committee endorsed this proposal. No objections<P>
|
|
were raised.<P>
|
|
<P>
|
|
</PRE>
|
|
<HR>
|
|
|
|
<A REL=NAVIGATOR HREF="../Front/StartPts.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Starting Points]" SRC="../Graphics/StartPts.gif" ALIGN=Bottom></A><A REL=TOC HREF="../Front/Contents.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Contents]" SRC="../Graphics/Contents.gif" ALIGN=Bottom></A><A REL=INDEX HREF="../Front/X_Master.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Index]" SRC="../Graphics/Index.gif" ALIGN=Bottom></A><A REL=INDEX HREF="../Front/X_Symbol.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Symbols]" SRC="../Graphics/Symbols.gif" ALIGN=Bottom></A><A REL=GLOSSARY HREF="../Body/26_a.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Glossary]" SRC="../Graphics/Glossary.gif" ALIGN=Bottom></A><A HREF="../Front/X3J13Iss.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Issues]" SRC="../Graphics/Issues.gif" ALIGN=Bottom></A><BR>
|
|
|
|
<A REL=COPYRIGHT HREF="../Front/Help.htm#Legal"><I>Copyright 1996-2005, LispWorks Ltd. All rights reserved.</I></A><P>
|
|
</BODY>
|
|
</HTML>
|