<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div><blockquote type="cite" class=""><div class="">On Apr 14, 2016, at 2:03 PM, Milos Rankovic <<a href="mailto:milos@milos-and-slavica.net" class="">milos@milos-and-slavica.net</a>> wrote:</div><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><blockquote type="cite" class=""><div class="">On 14 Apr 2016, at 21:36, John McCall <<a href="mailto:rjmccall@apple.com" class="">rjmccall@apple.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><span style="font-family: -webkit-standard; font-size: inherit; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">No, you just need Tree to conform to both ArrayLiteralConvertible and IntegerLiteralConvertible, and it implements the latter by building a Value out of it.</span></div></blockquote></div><br class=""><div class="">You mean this:</div><div class=""><br class=""></div><div class=""><div style="margin: 0px; line-height: normal;" class=""><font face="Menlo" size="2" class=""><span style="font-variant-ligatures: no-common-ligatures; color: rgb(200, 172, 229);" class="">public</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(200, 172, 229);" class="">enum</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> IntTree {</span></font></div><div style="margin: 0px; line-height: normal;" class=""><font face="Menlo" size="2" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><span class="Apple-tab-span" style="white-space:pre"> </span></span><span style="font-variant-ligatures: no-common-ligatures; color: #c8ace5" class="">case</span><span style="font-variant-ligatures: no-common-ligatures" class=""> Leaf(</span><span style="font-variant-ligatures: no-common-ligatures; color: #49a2d2" class="">Int</span><span style="font-variant-ligatures: no-common-ligatures" class="">)</span></font></div><div style="margin: 0px; line-height: normal;" class=""><font face="Menlo" size="2" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><span class="Apple-tab-span" style="white-space:pre"> </span></span><span style="font-variant-ligatures: no-common-ligatures; color: #c8ace5" class="">case</span><span style="font-variant-ligatures: no-common-ligatures" class=""> Branches([</span><span style="font-variant-ligatures: no-common-ligatures; color: #49a2d2" class="">IntTree</span><span style="font-variant-ligatures: no-common-ligatures" class="">])</span></font></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><font face="Menlo" size="2" class="">}</font></span></div><div style="margin: 0px; line-height: normal; min-height: 15px;" class=""><font face="Menlo" size="2" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></font></div><div style="margin: 0px; line-height: normal; color: rgb(73, 162, 210);" class=""><font face="Menlo" size="2" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #c8ace5" class="">extension</span><span style="" class=""> </span><span style="font-variant-ligatures: no-common-ligatures" class="">IntTree</span><span style="" class=""> : </span><span style="font-variant-ligatures: no-common-ligatures" class="">ArrayLiteralConvertible</span><span style="" class=""> {</span></font></div><div style="margin: 0px; line-height: normal;" class=""><font face="Menlo" size="2" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><span class="Apple-tab-span" style="white-space:pre"> </span></span><span style="font-variant-ligatures: no-common-ligatures; color: #c8ace5" class="">public</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #c8ace5" class="">init</span><span style="font-variant-ligatures: no-common-ligatures" class="">(arrayLiteral elements: </span><span style="font-variant-ligatures: no-common-ligatures; color: #49a2d2" class="">IntTree</span><span style="font-variant-ligatures: no-common-ligatures" class="">...) {</span></font></div><div style="margin: 0px; line-height: normal;" class=""><font face="Menlo" size="2" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><span class="Apple-tab-span" style="white-space:pre"> </span></span><span style="font-variant-ligatures: no-common-ligatures; color: #c8ace5" class="">self</span><span style="font-variant-ligatures: no-common-ligatures" class=""> = .</span><span style="font-variant-ligatures: no-common-ligatures; color: #49a2d2" class="">Branches</span><span style="font-variant-ligatures: no-common-ligatures" class="">(elements)</span></font></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><font face="Menlo" size="2" class=""><span class="Apple-tab-span" style="white-space:pre"> </span>}</font></span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><font face="Menlo" size="2" class="">}</font></span></div><div style="margin: 0px; line-height: normal; min-height: 15px;" class=""><font face="Menlo" size="2" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></font></div><div style="margin: 0px; line-height: normal; color: rgb(73, 162, 210);" class=""><font face="Menlo" size="2" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #c8ace5" class="">extension</span><span style="" class=""> </span><span style="font-variant-ligatures: no-common-ligatures" class="">IntTree</span><span style="" class=""> : </span><span style="font-variant-ligatures: no-common-ligatures" class="">IntegerLiteralConvertible</span><span style="" class=""> {</span></font></div><div style="margin: 0px; line-height: normal;" class=""><font face="Menlo" size="2" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><span class="Apple-tab-span" style="white-space:pre"> </span></span><span style="font-variant-ligatures: no-common-ligatures; color: #c8ace5" class="">public</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #c8ace5" class="">init</span><span style="font-variant-ligatures: no-common-ligatures" class="">(integerLiteral value: </span><span style="font-variant-ligatures: no-common-ligatures; color: #49a2d2" class="">IntegerLiteralType</span><span style="font-variant-ligatures: no-common-ligatures" class="">) {</span></font></div><div style="margin: 0px; line-height: normal;" class=""><font face="Menlo" size="2" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><span class="Apple-tab-span" style="white-space:pre"> </span></span><span style="font-variant-ligatures: no-common-ligatures; color: #c8ace5" class="">self</span><span style="font-variant-ligatures: no-common-ligatures" class=""> = .</span><span style="font-variant-ligatures: no-common-ligatures; color: #49a2d2" class="">Leaf</span><span style="font-variant-ligatures: no-common-ligatures" class="">(value)</span></font></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><font face="Menlo" size="2" class=""><span class="Apple-tab-span" style="white-space:pre"> </span>}</font></span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><font face="Menlo" size="2" class="">}</font></span></div><div style="margin: 0px; line-height: normal; min-height: 15px;" class=""><font face="Menlo" size="2" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></font></div><div style="margin: 0px; line-height: normal;" class=""><font face="Menlo" size="2" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #c8ace5" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> tree: </span><span style="font-variant-ligatures: no-common-ligatures; color: #49a2d2" class="">IntTree</span><span style="font-variant-ligatures: no-common-ligatures" class=""> = [[], </span><span style="font-variant-ligatures: no-common-ligatures; color: #ff2600" class="">1</span><span style="font-variant-ligatures: no-common-ligatures" class="">, [</span><span style="font-variant-ligatures: no-common-ligatures; color: #ff2600" class="">2</span><span style="font-variant-ligatures: no-common-ligatures" class="">, </span><span style="font-variant-ligatures: no-common-ligatures; color: #ff2600" class="">3</span><span style="font-variant-ligatures: no-common-ligatures" class="">], [[</span><span style="font-variant-ligatures: no-common-ligatures; color: #ff2600" class="">4</span><span style="font-variant-ligatures: no-common-ligatures" class="">, </span><span style="font-variant-ligatures: no-common-ligatures; color: #ff2600" class="">5</span><span style="font-variant-ligatures: no-common-ligatures" class="">], [</span><span style="font-variant-ligatures: no-common-ligatures; color: #ff2600" class="">6</span><span style="font-variant-ligatures: no-common-ligatures" class="">, </span><span style="font-variant-ligatures: no-common-ligatures; color: #ff2600" class="">7</span><span style="font-variant-ligatures: no-common-ligatures" class="">], [</span><span style="font-variant-ligatures: no-common-ligatures; color: #ff2600" class="">8</span><span style="font-variant-ligatures: no-common-ligatures" class="">, </span><span style="font-variant-ligatures: no-common-ligatures; color: #ff2600" class="">9</span><span style="font-variant-ligatures: no-common-ligatures" class="">]]]</span></font></div></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div><div class=""><blockquote type="cite" class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class="">you'll simply have to make your Tree less generic</div></div></blockquote></div><div class=""><br class=""></div><div class="">Yep, that’s the rub… With generic trees you can express yourself freely, whether you feel like:</div><div class=""><br class=""></div><div class=""><div style="margin: 0px; line-height: normal;" class=""><font face="Menlo" size="2" class=""><span style="font-variant-ligatures: no-common-ligatures; color: rgb(200, 172, 229);" class="">import</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> SpriteKit</span></font></div><div style="margin: 0px; line-height: normal; min-height: 15px;" class=""><font face="Menlo" size="2" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></font></div><div style="margin: 0px; line-height: normal;" class=""><font face="Menlo" size="2" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #c8ace5" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> actionTree: </span><span style="font-variant-ligatures: no-common-ligatures; color: #49a2d2" class="">Tree</span><span style="font-variant-ligatures: no-common-ligatures" class=""><</span><span style="font-variant-ligatures: no-common-ligatures; color: #49a2d2" class="">SKAction</span><span style="font-variant-ligatures: no-common-ligatures" class="">> = [</span></font></div><div style="margin: 0px; line-height: normal; color: rgb(145, 84, 15);" class=""><font face="Menlo" size="2" class=""><span style="" class=""><span class="Apple-tab-span" style="white-space:pre"> </span></span><span style="font-variant-ligatures: no-common-ligatures" class="">◊</span><span style="" class="">.</span><span style="font-variant-ligatures: no-common-ligatures" class="">waitForDuration</span><span style="" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #ff2600" class="">1</span><span style="" class="">),</span></font></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><font face="Menlo" size="2" class=""><span class="Apple-tab-span" style="white-space:pre"> </span>[</font></span></div><div style="margin: 0px; line-height: normal; color: rgb(145, 84, 15);" class=""><font face="Menlo" size="2" class=""><span style="" class=""><span class="Apple-tab-span" style="white-space:pre"> </span></span><span style="font-variant-ligatures: no-common-ligatures" class="">◊</span><span style="" class="">.</span><span style="font-variant-ligatures: no-common-ligatures" class="">fadeInWithDuration</span><span style="" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #ff2600" class="">1</span><span style="" class="">),</span></font></div><div style="margin: 0px; line-height: normal;" class=""><font face="Menlo" size="2" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><span class="Apple-tab-span" style="white-space:pre"> </span></span><span style="font-variant-ligatures: no-common-ligatures; color: #91540f" class="">◊</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #91540f" class="">scaleTo</span><span style="font-variant-ligatures: no-common-ligatures" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #ff2600" class="">1</span><span style="font-variant-ligatures: no-common-ligatures" class="">, duration: </span><span style="font-variant-ligatures: no-common-ligatures; color: #ff2600" class="">1</span><span style="font-variant-ligatures: no-common-ligatures" class="">)</span></font></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><font face="Menlo" size="2" class=""><span class="Apple-tab-span" style="white-space:pre"> </span>],</font></span></div><div style="margin: 0px; line-height: normal;" class=""><font face="Menlo" size="2" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><span class="Apple-tab-span" style="white-space:pre"> </span></span><span style="font-variant-ligatures: no-common-ligatures; color: #91540f" class="">◊</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #91540f" class="">playSoundFileNamed</span><span style="font-variant-ligatures: no-common-ligatures" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #64961d" class="">"TaDa"</span><span style="font-variant-ligatures: no-common-ligatures" class="">, waitForCompletion: </span><span style="font-variant-ligatures: no-common-ligatures; color: #c8ace5" class="">false</span><span style="font-variant-ligatures: no-common-ligatures" class="">)</span></font></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><font face="Menlo" size="2" class="">]</font></span></div></div><div class=""><br class=""></div><div class="">… or:</div><div class=""><br class=""></div><div class=""><div style="margin: 0px; line-height: normal; color: rgb(73, 162, 210);" class=""><font face="Menlo" size="2" class=""><span style="font-variant-ligatures: no-common-ligatures; color: rgb(200, 172, 229);" class="">let</span><span style="" class=""> johnny: </span><span style="font-variant-ligatures: no-common-ligatures;" class="">DictionaryTree</span><span style="" class=""><</span><span style="font-variant-ligatures: no-common-ligatures;" class="">String</span><span style="" class="">, </span><span style="font-variant-ligatures: no-common-ligatures;" class="">JSONValue</span><span style="" class="">> =</span></font></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><font face="Menlo" size="2" class="">[</font></span></div><div style="margin: 0px; line-height: normal; color: rgb(100, 150, 29);" class=""><font face="Menlo" size="2" class=""><span style="" class=""><span class="Apple-tab-span" style="white-space:pre"> </span></span><span style="font-variant-ligatures: no-common-ligatures" class="">"name"</span><span style="" class="">: </span><span style="font-variant-ligatures: no-common-ligatures; color: #91540f" class="">◊</span><span style="font-variant-ligatures: no-common-ligatures" class="">"Johnny Appleseed"</span><span style="" class="">,</span></font></div><div style="margin: 0px; line-height: normal; color: rgb(100, 150, 29);" class=""><font face="Menlo" size="2" class=""><span style="" class=""><span class="Apple-tab-span" style="white-space:pre"> </span></span><span style="font-variant-ligatures: no-common-ligatures" class="">"age"</span><span style="" class="">: </span><span style="font-variant-ligatures: no-common-ligatures; color: #91540f" class="">◊</span><span style="font-variant-ligatures: no-common-ligatures; color: #ff2600" class="">25</span><span style="" class="">,</span></font></div><div style="margin: 0px; line-height: normal; color: rgb(100, 150, 29);" class=""><font face="Menlo" size="2" class=""><span style="" class=""><span class="Apple-tab-span" style="white-space:pre"> </span></span><span style="font-variant-ligatures: no-common-ligatures" class="">"address"</span><span style="" class="">: [</span></font></div><div style="margin: 0px; line-height: normal; color: rgb(100, 150, 29);" class=""><font face="Menlo" size="2" class=""><span style="" class=""><span class="Apple-tab-span" style="white-space:pre"> </span></span><span style="font-variant-ligatures: no-common-ligatures" class="">"house_number"</span><span style="" class="">: </span><span style="font-variant-ligatures: no-common-ligatures; color: #91540f" class="">◊</span><span style="font-variant-ligatures: no-common-ligatures; color: #ff2600" class="">21</span><span style="" class="">,</span></font></div><div style="margin: 0px; line-height: normal; color: rgb(100, 150, 29);" class=""><font face="Menlo" size="2" class=""><span style="" class=""><span class="Apple-tab-span" style="white-space:pre"> </span></span><span style="font-variant-ligatures: no-common-ligatures" class="">"street"</span><span style="" class="">: </span><span style="font-variant-ligatures: no-common-ligatures; color: #91540f" class="">◊</span><span style="font-variant-ligatures: no-common-ligatures" class="">"2nd Street"</span><span style="" class="">,</span></font></div><div style="margin: 0px; line-height: normal; color: rgb(100, 150, 29);" class=""><font face="Menlo" size="2" class=""><span style="" class=""><span class="Apple-tab-span" style="white-space:pre"> </span></span><span style="font-variant-ligatures: no-common-ligatures" class="">"city"</span><span style="" class="">: </span><span style="font-variant-ligatures: no-common-ligatures; color: #91540f" class="">◊</span><span style="font-variant-ligatures: no-common-ligatures" class="">"New York"</span></font></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><font face="Menlo" size="2" class=""><span class="Apple-tab-span" style="white-space:pre"> </span>]</font></span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><font face="Menlo" size="2" class="">]</font></span></div></div><div class=""><br class=""></div><div class="">I’d just love to get rid of that prefix operator…</div></div></div></blockquote><div><br class=""></div></div>Note that all of your examples rely not just on recursion but on heterogeneous recursion, so the multiple-conformance idea doesn't work. Fundamentally, your trees have a payload type that needs to be constructible from different kinds of literal. It's appropriate to model that with conformance to multiple protocols. The ability to do that conditionally based on whether another type declares a conformance is called "conditional conformance", and it's already something we're strongly considering for the future; it's just not an easy feature to actually implement.<div class=""><div class=""><div class=""><div class=""><div class=""><div class=""><div class=""><div class=""><div class=""><div class=""><div class=""><br class=""></div><div class="">John.</div></div></div></div></div></div></div></div></div></div></div></body></html>