224 lines
7.8 KiB
Markdown
224 lines
7.8 KiB
Markdown
-----
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isHidden: false
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menupriority: 1
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kind: article
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created_at: 2011-10-20T11:39:36+02:00
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title: Increase the power of deficient languages.
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subtitle: Fractals with SVG and m4
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author_name: Yann Esposito
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author_uri: yannesposito.com
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tags:
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- m4
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- SVG
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- XSLT
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- XML
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- design
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- programming
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- fractal
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macros:
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svg: '<span class="sc">svg</span>'
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xml: '<span class="sc">xml</span>'
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xslt: '<span class="sc">xslt</span>'
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json: '<span class="sc">json</span>'
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-----
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blogimage("main.png","Yesod logo made in SVG and m4")
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begindiv(intro)
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<%= tldr %> How to use m4 to increase the power of deficient languages. Two examples: improve %xslt syntax and make fractal with %svg.
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enddiv
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%xml was a very nice idea about structuring data.
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Some people where so enthusiastic about %xml they saw it everywhere.
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The idea was: the future is %xml.
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Then some believed it would be a good idea to invent many %xml compatible format and even programming languages with %xml syntax.
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Happy! Happy! Joy! Joy!
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Unfortunately, %xml was made to transfert structured data.
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Not a format a human should see or edit directly.
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The sad reality is %xml syntax is simply verbose and ugly.
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Most of the time it shouldn't be a problem, as nobody should see it.
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In a perfect nice world, we should never deal directly with %xml but only use software which deal with it for us.
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Guess what?
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Our world isn't perfect. Too sad, a bunch of developer have to deal directly with this ugly %xml.
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Unfortunately %xml isn't the only case of misused format I know.
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You have many format for which it would be very nice to add variables, loops, functions...
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If like me you hate with passion %xslt or writing %xml,
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I will show you how you could deal with this bad format
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or language.
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## The %xslt Example
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Let's start by the worst case of misused %xml I know: %xslt.
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Any developer who had to deal with %xslt know how horrible it is.
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In order to reduce the verbosity of such a bad languages, there is a way.
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**`m4`**. Yes, the preprocessor you use when you program in `C` and `C++`.
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Here are some example:
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- Variable, instead of writing the natural `myvar = value`, here is the <sc>xslt</sc> way of doing this:
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<code class="xml">
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<xsl:variable name="myvar" select="value"/>
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</code>
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- Printing something. Instead of `print "Hello world!"` here is the <sc>xslt</sc> equivalent:
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<code class="xml">
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<xsl:text
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disable-output-escaping="yes"><![CDATA[Hello world!
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]]></xsl:text>
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</code>
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- printing the value of a variable, instead of `print myvar` the <sc>xslt</sc> is:
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<code class="xml">
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<xslt:value-of select="myvar"/>
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</code>
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- Just try to imagine how verbose it is to declare a function with this language.
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## The cure (m4 to the rescue)
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<code class="xml">
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<?xml version="1.0" standalone="yes"?> <!-- YES its %xml -->
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<!-- ← start a comment, then write some m4 directives:
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define(`ydef',`<xsl:variable name="$1" select="$2"/>')
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define(`yprint',`<xsl:text disable-output-escaping="yes"><![CDATA[$1]]></xsl:text>')
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define(`yshow',`<xsl:value-of select="$1"/>')
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-->
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<!-- Yes, %xml sucks to be read -->
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<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
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<!-- And it sucks even more to edit -->
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<xsl:template match="/">
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ydef(myvar,value)
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yprint(Hello world!)
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yshow(myvar)
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</xsl:template>
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</code>
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Now just compile this file:
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<code class="zsh">
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m4 myfile.m4 > myfile.xslt
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</code>
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Profit! Now <sc>xslt</sc> is more readable and easier to edit!
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## The cool part: Fractals!
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%svg is an %xml format used to represent vector graphics, it even support animations.
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At its beginning some people believed it would be the new Flash. Apparently, it will be more canvas + js.
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Let me show you the result:
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<a href="blogimagedirmain.svg">
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blogimage("main.png","Yesod logo made in SVG and m4")
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Click to view directly the %svg. It might slow down your computers if you have an old one.
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</a>
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The positionning of the "esod" text with regards to the reversed "λ" was done by changing position in firebug. I didn't had to manually regenerate to test.
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Making such a fractal is mostly:
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1. take a root element
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2. duplicate and transform it (scaling, translating, rotate)
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3. the result is a sub new element.
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4. repeat from 2 but by taking the sub new element as new root.
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5. Stop when recursion is deep enough.
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If I had to do this for each step, I had make a lot of copy/paste in my %svg, because the transformation is always the same, but I cannot say, use transformation named "titi". Then instead of manually copying some %xml, I used m4
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and here is the commented code:
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<code class="xml" file="yesodlogo.m4">
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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!--
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M4 Macros
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define(`YTRANSFORMONE', `scale(.43) translate(-120,-69) rotate(-10)')
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define(`YTRANSFORMTWO', `scale(.43) translate(-9,-67.5) rotate(10)')
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define(`YTRANSFORMTHREE', `scale(.43) translate(53,41) rotate(120)')
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define(`YGENTRANSFORM', `translate(364,274) scale(3)')
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define(`YTRANSCOMPLETE', `
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<g id="level_$1">
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<use style="opacity: .8" transform="YTRANSFORMONE" xlink:href="#level_$2" />
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<use style="opacity: .8" transform="YTRANSFORMTWO" xlink:href="#level_$2" />
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<use style="opacity: .8" transform="YTRANSFORMTHREE" xlink:href="#level_$2" />
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</g>
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<use transform="YGENTRANSFORM" xlink:href="#level_$1" />
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')
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-->
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<svg
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xmlns="http://www.w3.org/2000/svg"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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x="64" y="64" width="512" height="512" viewBox="64 64 512 512"
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id="svg2" version="1.1">
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<g id="level_0"> <!-- some group, if I want to add other elements -->
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<!-- the text "λ" -->
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<text id="lambda"
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fill="#333" style="font-family:Ubuntu; font-size: 100px"
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transform="rotate(180)">λ</text>
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</g>
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<!-- the text "esod" -->
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<text
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fill="#333"
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style="font-family:Ubuntu; font-size: 28px; letter-spacing: -0.10em"
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x="-17.3"
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y="69"
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transform="YGENTRANSFORM">esod</text>
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<!-- ROOT ELEMENT -->
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<use transform="YGENTRANSFORM" xlink:href="#level_0" />
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YTRANSCOMPLETE(1,0) <!-- First recursion -->
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YTRANSCOMPLETE(2,1) <!-- deeper -->
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YTRANSCOMPLETE(3,2) <!-- deeper -->
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YTRANSCOMPLETE(4,3) <!-- even deeper -->
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YTRANSCOMPLETE(5,4) <!-- Five level seems enough -->
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</svg>
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</code>
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and I compiled it to <sc>svg</sc> and then to <sc>png</sc> with:
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<code class="zsh">
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m4 yesodlogo.m4 > yesodlogo.svg && convert yesodlogo.svg yesodlogo.png
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</code>
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The main λ is duplicated 3 times. Each transformation is named by: `YTRANSFORMONE`, `YTRANSFORMTWO` and `YTRANSFORMTHREE`.
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Each transformation is just a similarity (translate + rotation + scale).
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Once fixed, we should now simply copy and repeat for each new level.
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Now it is time to talk about where the magic occurs: `YTRANSCOMPLETE`.
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This macro takes two arguments.
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The current depth and the preceding one.
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It duplicates using the three transformations the preceding level.
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- At level 0 there is only one λ,
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- at level 1 there is 3 λ,
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- at level 2 there is 9 λ
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- etc...
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At the final 5th level there is 3<sup>5</sup>=243 λ.
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All level combined have 3<sup>6</sup>-1 / 2 = 364 λ.
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I could preview the final result easily.
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Without the macro system, I would have to make 5 copy/paste + modifications for each try.
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## Conclusion
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It was fun to make a fractal in <sc>svg</sc>, but the interesting part is how to augment the power of a language using this preprocessor method.
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I used the <sc>xslt</sc> trick at work for example.
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I also used it to make include inside obscure format.
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If all you want is to generate a minimal static website withou using nanoc, jekyll or hakyll (ther are plenty other alternatives). You can consider using m4 to generate your <sc>html</sc> instead of copy/paste the menu and the footer, or using AJAX.
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Another usage I thouhgt about is to use m4
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to organize languages such as brainfuck.
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