<html><head><meta http-equiv="Content-Type" content="text/html charset=windows-1252"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On 22 Sep 2013, at 22:18, Scott McKay <<a href="mailto:swmckay@gmail.com">swmckay@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div dir="ltr">It's sad that this conses…</div></blockquote><div><br></div><div>True. I think I will use the single-value version for my own purposes. If this were to become part of a utilities library, it should probably best be split into a single-value ASSURE and a MULTIPLE-VALUE-ASSURE for multiple values, so you only pay for the overhead when you actually need it.</div><div><br></div><div>Pascal</div><br><blockquote type="cite"><div class="gmail_extra">On Sun, Sep 22, 2013 at 3:44 PM, Pascal Costanza <span dir="ltr"><<a href="mailto:pc@p-cos.net" target="_blank">pc@p-cos.net</a>></span> wrote:<br><div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word"><br><div><div>On 22 Sep 2013, at 20:45, Steve Haflich <<a href="mailto:shaflich@gmail.com" target="_blank">shaflich@gmail.com</a>> wrote:</div>
<br><blockquote type="cite"><p dir="ltr">No, it is generally possible to write portable setf expanders that work with multiple-value places provided the platform conforms to the ANS requirements. I have some extreme examples on another machine I may share to the list later.</p><p dir="ltr">I think to be portable transparent assure would need to collect and return multiple values, with the hope that the compiler would eliminate that stuff if the place were a single-value form like a variable or known function.<br>
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</blockquote></div><div>OK, it seems you mean something like this:</div><div><br></div><div><div>(defmacro assure (type form &environment env)</div><div class="im"><div> (multiple-value-bind</div><div> (vars vals store-vars writer reader)</div>
</div><div> (get-setf-expansion ,form env)</div><div> (declare (ignore store-vars writer))</div><div> `(let* ,(mapcar 'list vars vals)</div><div> (check-type ,reader ,type)</div><div> ,reader)))</div>
</div><div><br></div><div>However, this is not good enough. Something as simple as (assure integer (+ x y)) already doesn't work. The requirement that form is a generalized reference is an artifact that comes from check-type, but that shouldn't leak through.</div>
<div><br></div><div>I came up with another version. I believe this should work:</div><div><br></div><div><div>(defmacro assure (type form)</div><div class="im"><div> (let ((values (copy-symbol 'values)))</div><div> `(let ((,values (multiple-value-list ,form)))</div>
</div><div> (declare (dynamic-extent values))</div><div> (etypecase (values-list ,values)</div><div> (,type (values-list ,values))))))</div></div><div><br></div><div>…except that this also doesn't work in some Common Lisp implementations for multiple values, but I think it should and those implementations need to be fixed.</div>
<div class="im"><div><br></div><div><br></div><div>Pascal</div><br><div>
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--</div><div>Pascal Costanza</div><div>The views expressed in this email are my own, and not those of my employer.</div><div><br></div></span><br>
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<span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><div>--</div><div>Pascal Costanza</div><div>The views expressed in this email are my own, and not those of my employer.</div><div><br></div></span><br class="Apple-interchange-newline">
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