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<TITLE>CLHS: Issue ASSERT-ERROR-TYPE Writeup</TITLE>
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<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/iss015_w.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="../Issues/iss016.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="../Issues/iss017_w.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<H2>Issue ASSERT-ERROR-TYPE Writeup</H2>
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<PRE><B>Status:</B> Proposal <A REL=DEFINITION HREF="../Body/a_error.htm#error"><B>ERROR</B></A> accepted 12/91<P>
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<B>Issue:</B> <A HREF="iss016.htm">ASSERT-ERROR-TYPE</A><P>
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<B>Forum:</B> Cleanup<P>
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<B>References:</B> <A REL=DEFINITION HREF="../Body/m_assert.htm#assert"><B>ASSERT</B></A> (Condition System, Revision #18, p27)<P>
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<B>Category:</B> CHANGE<P>
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<B>Edit history:</B> 15-Mar-91, 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 condition system proposal says that <A REL=DEFINITION HREF="../Body/m_assert.htm#assert"><B>ASSERT</B></A> signals <A REL=DEFINITION HREF="../Body/e_smp_er.htm#simple-error"><B>SIMPLE-ERROR</B></A><P>
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if the datum is omitted. This unnecessarily restricts an <P>
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implementation's options.<P>
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<P>
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<B>Proposal (ASSERT-ERROR-TYPE:ERROR):<P>
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</B><P>
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Define that if the datum is omitted, <A REL=DEFINITION HREF="../Body/m_assert.htm#assert"><B>ASSERT</B></A> signals <A REL=DEFINITION HREF="../Body/a_error.htm#error"><B>ERROR</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_hand_1.htm#handler-case"><B>HANDLER-CASE</B></A> (<A REL=DEFINITION HREF="../Body/m_hand_1.htm#handler-case"><B>HANDLER-CASE</B></A> (<A REL=DEFINITION HREF="../Body/m_assert.htm#assert"><B>ASSERT</B></A> <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A>) (<A REL=DEFINITION HREF="../Body/e_smp_er.htm#simple-error"><B>SIMPLE-ERROR</B></A> 1)) (<A REL=DEFINITION HREF="../Body/a_error.htm#error"><B>ERROR</B></A> 2))<P>
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<P>
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Under Conditions System revision #18, this must return 1.<P>
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Under proposal <A HREF="iss016.htm">ASSERT-ERROR-TYPE:ERROR</A>, this might return either 1 or 2.<P>
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<P>
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<B>Rationale:<P>
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</B><P>
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This leaves an implementation free to experiment with error types <P>
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specific to assertions. Since the user is free to specify whatever<P>
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type he needs, he can always work around any implementation-specific<P>
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type in any way he wants.<P>
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<P>
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<B>Current Practice:<P>
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</B><P>
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In Symbolics Genera 8.1, the test case returns 1.<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. (Since <A REL=DEFINITION HREF="../Body/e_smp_er.htm#simple-error"><B>SIMPLE-ERROR</B></A> is a subtype of <A REL=DEFINITION HREF="../Body/a_error.htm#error"><B>ERROR</B></A>, no change is forced.<P>
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This just adds flexibility to implementations which want to do this <P>
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differently.<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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Little or none. There are probably very few people who are <P>
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specifically doing <A REL=DEFINITION HREF="../Body/m_hand_1.htm#handler-case"><B>HANDLER-CASE</B></A> for <A REL=DEFINITION HREF="../Body/e_smp_er.htm#simple-error"><B>SIMPLE-ERROR</B></A> with the intent<P>
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of specifically catching <A REL=DEFINITION HREF="../Body/m_assert.htm#assert"><B>ASSERT</B></A>.<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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Implementations have their hands tied unnecessarily.<P>
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<P>
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<B>Benefits:<P>
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</B><P>
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Aesthetics. Implementation flexibility.<P>
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<P>
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<B>Aesthetics:<P>
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</B><P>
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Makes language more consistent in that this was the only place where<P>
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<A REL=DEFINITION HREF="../Body/e_smp_er.htm#simple-error"><B>SIMPLE-ERROR</B></A> was forced in a situation where the user wasn't supplying<P>
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a format string.<P>
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<P>
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<B>Discussion:<P>
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</B><P>
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This issue was raised by Barrett several meetings ago, but was never<P>
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formally written up.<P>
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<P>
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Pitman supports this.<P>
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<P>
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</PRE>
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