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<H2>Issue DEFSTRUCT-SLOTS-CONSTRAINTS-NUMBER Writeup</H2>
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<PRE><B>Issue:</B> <A HREF="iss120.htm">DEFSTRUCT-SLOTS-CONSTRAINTS-NUMBER</A><P>
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<B>References:</B> CLtL p.307 & 86-003 p.4<P>
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<B>Category:</B> CHANGE<P>
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<B>Edit history:</B> Revision 1 by Skona Brittain 05/13/88<P>
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<P>
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<B>Problem Description:<P>
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</B><P>
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Structures defined by <A REL=DEFINITION HREF="../Body/m_defstr.htm#defstruct"><B>defstruct</B></A> currently are required to have at least<P>
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one slot. This seems to have been a mistake in the design of the language.<P>
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<P>
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<B>Proposal (DEFSTRUCT-SLOTS-CONSTRAINTS-NUMBER:ALLOW-ZERO):<P>
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</B><P>
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Allow a call to <A REL=DEFINITION HREF="../Body/m_defstr.htm#defstruct"><B>defstruct</B></A> to have zero slot-descriptions.<P>
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i.e. change the + to a * in the syntax of calls to <A REL=DEFINITION HREF="../Body/m_defstr.htm#defstruct"><B>defstruct</B></A> <P>
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given at the bottom of page 307 of CLtL.<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/m_defstr.htm#defstruct"><B>defstruct</B></A> s), which is not allowed according to CLtL, would be allowed.<P>
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<P>
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<B>Rationale:<P>
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</B><P>
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The current restriction is in marked contrast to the generality allowed <P>
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elsewhere in the language. And removing it slightly increases the <P>
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usefulness of <A REL=DEFINITION HREF="../Body/m_defstr.htm#defstruct"><B>defstruct</B></A> - by allowing the zero slot case when it may be <P>
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deemed useful and by not requiring a check for it when it doesn't matter.<P>
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<P>
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<B>Current Practice:<P>
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</B><P>
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KCL allows zero slots. <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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None for implementations that currently allow zero slots.<P>
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Very slight for others.<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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None.<P>
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<P>
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<B>Benefits:<P>
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</B><P>
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Slightly increases the usefulness of <A REL=DEFINITION HREF="../Body/m_defstr.htm#defstruct"><B>defstruct</B></A> and is aesthetic.<P>
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<P>
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<B>Aesthetics:<P>
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</B><P>
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In general, it is more aesthetic to allow for generality rather than to<P>
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specifically prohibit a particular case. And the generality in this case <P>
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is consistent with that of many other features of the language, such as <P>
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that arrays can be empty, functions like + and list can take zero arguments, <P>
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etc.<P>
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<P>
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<B>Discussion: <P>
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</B><P>
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Although this issue was mentioned in Guy's original issues file, it has<P>
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not been officially discussed since.<P>
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</PRE>
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