<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=""><br class=""><div><blockquote type="cite" class=""><div class="">On Feb 2, 2016, at 11:12 AM, Austin Zheng <<a href="mailto:austinzheng@gmail.com" class="">austinzheng@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html charset=us-ascii" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Hmm...the rationale that Joe provided makes a lot of sense.</div></div></blockquote><div><br class=""></div><div>If it wasn’t clear, that rationale is from the core team discussion of SE-0021. </div><div><br class=""></div><div>I’m very strongly -1 on this.</div><div><br class=""></div><span class="Apple-tab-span" style="white-space:pre"> </span>- Doug</div><div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">One question - is the explicit closure syntax amenable to multiple levels of currying? In particular, what are the scoping rules for the placeholders $<i class="">n </i>- are they limited to the immediate closure within which they appear, or can they be used within further-nested closures?</div><div class=""><br class=""></div><div class="">Best,</div><div class="">Austin<br class=""><div class=""><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Feb 2, 2016, at 11:01 AM, Douglas Gregor via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html charset=us-ascii" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Feb 2, 2016, at 9:33 AM, Erica Sadun via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html charset=us-ascii" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">First draft. Let's go Scala!<div class=""><br class=""></div><div class="">-- E</div><div class=""><br class=""></div><div class=""><h1 style="box-sizing: border-box; font-size: 2.25em; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.2; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class="">Automating Partial Application via Wildcards</h1><ul style="box-sizing: border-box; padding: 0px 0px 0px 2em; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);" class=""><li style="box-sizing: border-box;" class="">Proposal: TBD</li><li style="box-sizing: border-box;" class="">Author(s): <a href="http://github.com/erica" style="box-sizing: border-box; background-color: transparent; color: rgb(64, 120, 192); text-decoration: none;" class="">Erica Sadun</a>, <a href="http://github.com/DeFrenZ" style="box-sizing: border-box; background-color: transparent; color: rgb(64, 120, 192); text-decoration: none;" class="">Davide De Franceschi</a></li><li style="box-sizing: border-box;" class="">Status: TBD</li><li style="box-sizing: border-box;" class="">Review manager: TBD</li></ul><h2 style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.225; font-size: 1.75em; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a id="user-content-introduction" class="anchor" href="https://gist.github.com/erica/6327981d42eb9be6b4d2#introduction" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; color: rgb(64, 120, 192); text-decoration: none; display: inline-block; padding-right: 2px; margin-left: -18px; line-height: 1;"><svg aria-hidden="true" class="octicon octicon-link" height="16" role="img" version="1.1" viewBox="0 0 16 16" width="16"><path d="M4 9h1v1h-1c-1.5 0-3-1.69-3-3.5s1.55-3.5 3-3.5h4c1.45 0 3 1.69 3 3.5 0 1.41-0.91 2.72-2 3.25v-1.16c0.58-0.45 1-1.27 1-2.09 0-1.28-1.02-2.5-2-2.5H4c-0.98 0-2 1.22-2 2.5s1 2.5 2 2.5z m9-3h-1v1h1c1 0 2 1.22 2 2.5s-1.02 2.5-2 2.5H9c-0.98 0-2-1.22-2-2.5 0-0.83 0.42-1.64 1-2.09v-1.16c-1.09 0.53-2 1.84-2 3.25 0 1.81 1.55 3.5 3 3.5h4c1.45 0 3-1.69 3-3.5s-1.5-3.5-3-3.5z"></path></svg></a>Introduction</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);" class=""><a href="https://github.com/apple/swift-evolution/blob/master/proposals/0002-remove-currying.md" style="box-sizing: border-box; background-color: transparent; color: rgb(64, 120, 192); text-decoration: none;" class="">SE-0002</a> has been accepted for Swift 3.0. That proposal removes currying func declaration syntax from Swift. It reasons that currying introduces unnecessary language and implementation complexity and is easily replaced with chained function return types. </p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);" class="">Because of SE-0002, this curried example:</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><pre style="box-sizing: border-box; overflow: auto; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; padding: 16px; background-color: rgb(247, 247, 247); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-wrap: normal; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">public</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">projectFunctionToCoordinateSystem</span>(function <span class="pl-smi" style="box-sizing: border-box;">f</span>: FunctionType)(p0: CGPoint, p1: CGPoint)(x: CGFloat) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> CGPoint</pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);" class="">becomes</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><pre style="box-sizing: border-box; overflow: auto; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; padding: 16px; background-color: rgb(247, 247, 247); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-wrap: normal; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">public</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">projectFunctionToCoordinateSystem</span>(function <span class="pl-smi" style="box-sizing: border-box;">f</span>: FunctionType) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> (p0: CGPoint, p1: CGPoint) -> (x: CGFloat) -> CGPoint </pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);" class="">in Swift 3.</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);" class="">It's mechanically simple to re-introduce partial application but the current solution adds unnecessary nesting and complicated closure declarations, as you see in the following Swift 3 version of this projection function.</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><pre style="box-sizing: border-box; overflow: auto; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; padding: 16px; background-color: rgb(247, 247, 247); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-wrap: normal; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">public</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">projectFunctionToCoordinateSystem</span>(function <span class="pl-smi" style="box-sizing: border-box;">f</span>: FunctionType) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> (p0: CGPoint, p1: CGPoint) -> (x: CGFloat) -> CGPoint {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> { p0, p1 <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">in</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> { x <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">in</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> (dx, dy) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> (p1<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>x <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-</span> p0<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>x, p1<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>y <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-</span> p0<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>y)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> (magnitude, theta) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> (hypot(dy, dx), atan2(dy, dx)) <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">// Thanks loooop</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> outPoint <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> CGPoint(x: x <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">*</span> magnitude, y: f(x) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">*</span> magnitude)
outPoint <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> CGPointApplyAffineTransform(outPoint, CGAffineTransformMakeRotation(theta))
outPoint <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> CGPointApplyAffineTransform(outPoint, CGAffineTransformMakeTranslation(p0<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>x, p0<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>y))
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> CGPoint(x: outPoint<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>x, y: outPoint<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>y)
}
}
}</pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);" class="">SE-0002 mentions the possibility of introducing Scala-style free-form partial implementation as a future step. This proposal requests that a Scala-style wildcard feature be adopted into Swift by introducing a form of automatic partial application.</p><h2 style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.225; font-size: 1.75em; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a id="user-content-detail-design" class="anchor" href="https://gist.github.com/erica/6327981d42eb9be6b4d2#detail-design" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; color: rgb(64, 120, 192); text-decoration: none; display: inline-block; padding-right: 2px; margin-left: -18px; line-height: 1;"><svg aria-hidden="true" class="octicon octicon-link" height="16" role="img" version="1.1" viewBox="0 0 16 16" width="16"><path d="M4 9h1v1h-1c-1.5 0-3-1.69-3-3.5s1.55-3.5 3-3.5h4c1.45 0 3 1.69 3 3.5 0 1.41-0.91 2.72-2 3.25v-1.16c0.58-0.45 1-1.27 1-2.09 0-1.28-1.02-2.5-2-2.5H4c-0.98 0-2 1.22-2 2.5s1 2.5 2 2.5z m9-3h-1v1h1c1 0 2 1.22 2 2.5s-1.02 2.5-2 2.5H9c-0.98 0-2-1.22-2-2.5 0-0.83 0.42-1.64 1-2.09v-1.16c-1.09 0.53-2 1.84-2 3.25 0 1.81 1.55 3.5 3 3.5h4c1.45 0 3-1.69 3-3.5s-1.5-3.5-3-3.5z"></path></svg></a>Detail Design</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);" class="">The proposed design replaces a Swift 3 curried signature like this: </p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><pre style="box-sizing: border-box; overflow: auto; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; padding: 16px; background-color: rgb(247, 247, 247); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-wrap: normal; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">public</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">projectFunctionToCoordinateSystem</span>(function <span class="pl-smi" style="box-sizing: border-box;">f</span>: FunctionType) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> (p0: CGPoint, p1: CGPoint) -> (x: CGFloat) -> CGPoint</pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);" class="">with a non-curried, fully qualified call like this:</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><pre style="box-sizing: border-box; overflow: auto; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; padding: 16px; background-color: rgb(247, 247, 247); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-wrap: normal; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">public</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">projectFunctionToCoordinateSystem</span>(function <span class="pl-smi" style="box-sizing: border-box;">f</span>: FunctionType, p0: CGPoint, p1: CGPoint, x: CGFloat) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> CGPoint</pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);" class="">When called with wildcard tokens, the function is partially applied using the supplied arguments. For example:</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><pre style="box-sizing: border-box; overflow: auto; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; padding: 16px; background-color: rgb(247, 247, 247); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-wrap: normal; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> partial1 <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> projectFunctionToCoordinateSystem(function: mySinFunction, p0: p0, p1: p1, x: _)
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">// partial1(x: xValue)</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> partial2 <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> projectFunctionToCoordinateSystem(function: mySinFunction, p0: <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>zero, p1: _, x: _)
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">// partial2(p1: p1Value, x: xValue) </span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">// or</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">// let partial3 = partial2(p1: p1Value, x: _); partial3(x: 0.25)</span></pre></div></div></div></div></blockquote>In the SE-0021 acceptance rationale at </div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span><a href="http://article.gmane.org/gmane.comp.lang.swift.evolution/3961/match=accepted+0021" class="">http://article.gmane.org/gmane.comp.lang.swift.evolution/3961/match=accepted+0021</a></div><div class=""><br class=""></div><div class="">Joe Groff sayeth:</div><div class=""><br class=""></div><blockquote style="margin: 0 0 0 40px; border: none; padding: 0px;" class=""><div class=""><span class=""><font face="HelveticaNeue" class="">A number of contributors proposed an alternative syntax, using a placeholder in the argument value position:</font></span></div><div class=""><div class=""><span class=""><font face="HelveticaNeue" class=""><br class=""></font></span></div></div><div class=""><blockquote class=""><div class=""><span class=""><font face="HelveticaNeue" class="">let x = Foo.bar(_, bas: _)</font></span></div></blockquote></div><div class=""><blockquote class=""><div class=""><span class=""><font face="HelveticaNeue" class=""><br class=""></font></span></div></blockquote></div><div class=""><span style="background-color: rgb(255, 255, 255);" class=""><font face="HelveticaNeue" class="">with the idea that this could potentially generalize to partial application syntax. We don't think this is a good direction for Swift for a couple of reasons. Swift already has fairly compact syntax for forming closures over partially applied functions, { Foo.bar($0, bas: $1) }. It may not be everyone's aesthetic cup of tea, but this notation has several important advantages. The braces unambiguously delineate the boundaries of the closure, which is a subtle problem with Scala-like approaches. The braces also provide a visual cue that capture is occurring. The $n placeholders are also more general since they allow for reordering of arguments. '_' in particular is also a poor choice of placeholder, since in other contexts where it's used, it's meant as a "black hole" for value binding in patterns rather than as a placeholder for a meaningful bound value.</font></span></div></blockquote><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- Doug</div><div class=""><br class=""></div><br class=""></div>_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br class=""></div></blockquote></div><br class=""></div></div></div></div></blockquote></div><br class=""></body></html>