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93 lines
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<H2>Issue DEFVAR-DOCUMENTATION Writeup</H2>
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<PRE><B>Issue:</B> <A HREF="iss123.htm">DEFVAR-DOCUMENTATION</A><P>
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<B>References:</B> <A REL=DEFINITION HREF="../Body/m_defpar.htm#defvar"><B>DEFVAR</B></A>, <A REL=DEFINITION HREF="../Body/m_defpar.htm#defparameter"><B>DEFPARAMETER</B></A>, <A REL=DEFINITION HREF="../Body/m_defcon.htm#defconstant"><B>DEFCONSTANT</B></A> (pp68-9)<P>
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<B>Category:</B> CLARIFICATION<P>
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<B>Edit history:</B> 30-Jun-87, Version 1 by Pitman<P>
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23-Nov-87, Version 2 by Masinter<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 is not explicit about whether the documentation part of <A REL=DEFINITION HREF="../Body/m_defpar.htm#defvar"><B>DEFVAR</B></A>,<P>
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<A REL=DEFINITION HREF="../Body/m_defpar.htm#defparameter"><B>DEFPARAMETER</B></A>, and <A REL=DEFINITION HREF="../Body/m_defcon.htm#defconstant"><B>DEFCONSTANT</B></A> special forms is evaluated.<P>
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<P>
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<B>Proposal (DEFVAR-DOCUMENTATION:UNEVALUATED):<P>
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</B><P>
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Clarify that the documentation part of <A REL=DEFINITION HREF="../Body/m_defpar.htm#defvar"><B>DEFVAR</B></A>, <A REL=DEFINITION HREF="../Body/m_defpar.htm#defparameter"><B>DEFPARAMETER</B></A>, and <A REL=DEFINITION HREF="../Body/m_defcon.htm#defconstant"><B>DEFCONSTANT</B></A><P>
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special forms is not evaluated. That is, it must be a literal string, not a form<P>
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which evaluates to a string.<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/m_defpar.htm#defvar"><B>DEFVAR</B></A> *MY-VARIABLE* (CONSTRUCT-INITIAL-VALUE) "A <A REL=DEFINITION HREF="../Body/f_docume.htm#documentation"><B>documentation</B></A> string") ; OK<P>
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(<A REL=DEFINITION HREF="../Body/m_defpar.htm#defvar"><B>DEFVAR</B></A> *MY-VARIABLE* (CONSTRUCT-INITIAL-VALUE) GENERIC-DOCUMENTATION-STRING) ;<P>
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would be an error<P>
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<P>
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<B>Rationale:<P>
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</B><P>
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To ensure portability, implementations must agree on whether or not this<P>
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position is evaluated. Specifying that the position is unevaluated is the<P>
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conservative thing to suggest, and consistent with the (unevaluated)<P>
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documentation strings in <A REL=DEFINITION HREF="../Body/m_defun.htm#defun"><B>DEFUN</B></A>, <A REL=DEFINITION HREF="../Body/m_defstr.htm#defstruct"><B>DEFSTRUCT</B></A>.<P>
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<P>
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<B>Current Practice:<P>
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</B><P>
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Some implementations evaluate this position. Others do not. <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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Implementations that did not already check might usefully add a check in the<P>
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macro expansion for <A REL=DEFINITION HREF="../Body/m_defpar.htm#defvar"><B>DEFVAR</B></A>, <A REL=DEFINITION HREF="../Body/m_defpar.htm#defparameter"><B>DEFPARAMETER</B></A> and <A REL=DEFINITION HREF="../Body/m_defcon.htm#defconstant"><B>DEFCONSTANT</B></A> to assert that the<P>
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<A REL=DEFINITION HREF="../Body/f_docume.htm#documentation"><B>DOCUMENTATION</B></A>, if supplied, was a string. The change is likely 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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Code which uses other than a literal string is not portable, so no portable<P>
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programs will be broken. Some non-portable programs which rely on a particular<P>
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vendor's interpretation would have to be rewritten. Automatic tools to detect<P>
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most offending cases could trivially be constructed. (We know of no current<P>
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uses.)<P>
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<P>
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<B>Benefits:<P>
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</B><P>
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Code portability would be improved. Some programming environment tools might<P>
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assume that documentation strings were determinable without evaluation.<P>
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<P>
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<B>Aesthetics:<P>
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</B><P>
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Slight improvement; this implies consistent treatment for documentation strings<P>
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in all defining forms.<P>
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<P>
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<B>Discussion:<P>
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</B><P>
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We think this is a good idea.<P>
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<P>
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</PRE>
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