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104 lines
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<H2>Issue DEFSTRUCT-INCLUDE-DEFTYPE Writeup</H2>
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<PRE><B>Issue:</B> <A HREF="iss115.htm">DEFSTRUCT-INCLUDE-DEFTYPE</A><P>
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<B>Forum:</B> Editorial<P>
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<B>References:</B> <A REL=DEFINITION HREF="../Body/m_defstr.htm#defstruct"><B>DEFSTRUCT</B></A>'s :INCLUDE option (pp312-314)<P>
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<B>Category:</B> CLARIFICATION<P>
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<B>Edit history:</B> 01-Mar-91, Version 1 by Pitman<P>
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<B>Status:</B> For X3J13 consideration<P>
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<P>
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<B>Problem Description:<P>
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</B><P>
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From time to time, people ask whether they can specify in a :INCLUDE<P>
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to <A REL=DEFINITION HREF="../Body/m_defstr.htm#defstruct"><B>DEFSTRUCT</B></A> the name of a type which is defined by <A REL=DEFINITION HREF="../Body/m_deftp.htm#deftype"><B>DEFTYPE</B></A> to expand<P>
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into a type that was defined by <A REL=DEFINITION HREF="../Body/m_defstr.htm#defstruct"><B>DEFSTRUCT</B></A>.<P>
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<P>
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<B>Proposal (DEFSTRUCT-INCLUDE-DEFTYPE:EXPLICITLY-UNDEFINED):<P>
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</B><P>
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Clarify that the only names which are permissible as type names to<P>
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the :INCLUDE option of <A REL=DEFINITION HREF="../Body/m_defstr.htm#defstruct"><B>DEFSTRUCT</B></A> are actual names previously defined<P>
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by <A REL=DEFINITION HREF="../Body/m_defstr.htm#defstruct"><B>DEFSTRUCT</B></A>.<P>
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<P>
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Clarify that one implication of this is that the consequences are <P>
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undefined if a type given to <A REL=DEFINITION HREF="../Body/m_defstr.htm#defstruct"><B>DEFSTRUCT</B></A>'s :INCLUDE option is a type<P>
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defined by <A REL=DEFINITION HREF="../Body/m_deftp.htm#deftype"><B>DEFTYPE</B></A>, even if it expands into a type defined by <A REL=DEFINITION HREF="../Body/m_defstr.htm#defstruct"><B>DEFSTRUCT</B></A>.<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> FOO A B)<P>
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<P>
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(<A REL=DEFINITION HREF="../Body/m_deftp.htm#deftype"><B>DEFTYPE</B></A> FU () 'FOO)<P>
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<P>
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(<A REL=DEFINITION HREF="../Body/m_defstr.htm#defstruct"><B>DEFSTRUCT</B></A> (BAR (:INCLUDE FU)) C)<P>
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<P>
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<B>Rationale:<P>
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</B><P>
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Permitting DEFTYPE-defined types here might open the door to other<P>
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inconsistencies with DEFTYPE-defined types not being accepted in other<P>
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`reasonable' places.<P>
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<P>
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Most implementations probably don't allow this and a change would<P>
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be extra work for implementors.<P>
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<P>
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<B>Current Practice:<P>
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</B><P>
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Symbolics Genera signals an error if the :INCLUDE'd type was not<P>
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specifically defined by <A REL=DEFINITION HREF="../Body/m_defstr.htm#defstruct"><B>DEFSTRUCT</B></A>.<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. "The consequences are undefined" leaves implementations free to<P>
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do whatever they want.<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. Users de facto can't really rely on this now so portable<P>
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programs shouldn't be effected.<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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Some users will continue to be puzzled about whether the perceived-to-be <P>
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fascist behavior of some implementations is what was intended.<P>
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<P>
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<B>Benefits:<P>
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</B><P>
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Users will know what to expect.<P>
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<P>
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<B>Aesthetics:<P>
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</B><P>
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Doing the full job of making DEFTYPE-defined types acceptable in any<P>
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place might be aesthetic, but that's not what is proposed here, and making<P>
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a lot of little special case exceptions probably isn't so aesthetic.<P>
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<P>
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<B>Discussion:<P>
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</B><P>
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Pitman supports this proposal.<P>
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</PRE>
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