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89 lines
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<H2>Issue COMPILE-ARGUMENT-PROBLEMS-AGAIN Writeup</H2>
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<PRE><B>Issue:</B> <A HREF="iss058.htm">COMPILE-ARGUMENT-PROBLEMS-AGAIN</A><P>
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<B>References:</B> COMPILE-ARGUMENT-PROBLEMS, draft 10.156 p.3-52<P>
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<B>Category:</B> CHANGE<P>
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<B>Edit History:</B> 9-Dec-91, Version 1, by Moon<P>
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<B>Status:</B> Passed 10-Dec-91; 11-0 on part 1, 9-1-1 on part 2<P>
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<P>
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<B>Problem Description:<P>
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</B><P>
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Cleanup COMPILE-ARGUMENT-PROBLEMS:CLARIFY created a couple of problems:<P>
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<P>
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(1) It says "The consequences of calling <A REL=DEFINITION HREF="../Body/f_cmp.htm#compile"><B>COMPILE</B></A> on a function that is already<P>
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compiled are unspecified" but the spec doesn't <A REL=DEFINITION HREF="../Body/f_provid.htm#provide"><B>provide</B></A> any way to create a<P>
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function that is guaranteed not to be compiled already. In fact the example<P>
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at the top of page 3-52 is invalid because of this.<P>
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<P>
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(2) It says the consequences are undefined "if the function to be compiled was<P>
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defined interpretively in a non-null lexical environment", but a non-null<P>
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lexical environment doesn't imply a closure. It might just have declarations in<P>
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it. The original motivation was "Many implementations cannot correctly compile<P>
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functions that are defined interpretively in a non-null lexical environment,<P>
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because the compiler and interpreter use different representations for<P>
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closures."<P>
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<P>
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<B>Proposal (COMPILE-ARGUMENT-PROBLEMS-AGAIN:FIX):<P>
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</B><P>
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(1) Remove the quoted text and specify that <A REL=DEFINITION HREF="../Body/f_cmp.htm#compile"><B>COMPILE</B></A> either returns the function<P>
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it is given or returns an equivalent function, but in any case returns a<P>
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<A REL=DEFINITION HREF="../Body/t_cmpd_f.htm#compiled-function"><B>COMPILED-FUNCTION</B></A>.<P>
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<P>
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(2) Replace the quoted text with "if the lexical environment surrounding the<P>
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function to be compiled contains any bindings other than macros, symbol macros,<P>
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or declarations".<P>
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<P>
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<B>Rationale:<P>
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</B><P>
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(1) Given a function that is already compiled, <A REL=DEFINITION HREF="../Body/f_cmp.htm#compile"><B>COMPILE</B></A> can simply return it.<P>
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<P>
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(2) Bindings that minimal compilation would remove shouldn't prevent <A REL=DEFINITION HREF="../Body/f_cmp.htm#compile"><B>COMPILE</B></A><P>
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from working, since no closure would be required.<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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(1) Trivial.<P>
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(2) Might <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>require</B></A> some work, depending on what the interpreter does with<P>
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macros in the lexical environment of an interpreted function.<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. This is an upward-compatible change.<P>
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<P>
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<B>Benefits:<P>
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</B><P>
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(1) Users don't have to insert extra <A REL=DEFINITION HREF="../Body/f_cmpd_f.htm#compiled-function-p"><B>COMPILED-FUNCTION-P</B></A> checks.<P>
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(2) Make the language less restrictive.<P>
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<P>
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<B>Discussion:<P>
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</B><P>
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Parts 1 and 2 should be voted separately.<P>
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</PRE>
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