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POCast Scala String to StringContext and virtually forward references
 

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    <p>In Scala 2.10.0-RC1 there's a wonderful feature, the <em><a href="http://docs.scala-lang.org/sips/pending/string-interpolation.html" rel="nofollow">String Interpolation</a></em>.</p> <p>This works like this:</p> <pre><code>scala&gt; val x = 1 x: Int = 1 scala&gt; val y = s"Interpolated String $x" y: String = Interpolated String 1 </code></pre> <p>But I'm building a internal DSL with Scala, and therefore I need to handle with a sort of <em>forward references</em>. That you have in mind, what the DSL looks like (it's for documentation generation):</p> <pre><code>object Main { § &gt; "Heading" § &gt;&gt; "Subheading" ++ txt """ Lorem ipsum Abb. ${Main.fig.number} dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. """ val fig = ++ figure( src="https://...", desc="example figure" ) } </code></pre> <p>But the problem looks semantically like this:</p> <pre><code>object X { val y = s"$x with reverse reference" val x = 3 } </code></pre> <p>And this doesn't work, because of the virtually forward reference. I can write <code>x</code> as <code>lazy val</code>, but the compiler moves <code>x</code> and makes it for <code>y</code> available. But for my DSL design the order of <code>y</code> and <code>x</code> <em>must</em> be preserved!</p> <p>So far my solution is a closure, like this:</p> <pre><code>object X { val y = () =&gt; s"$x with reverse reference" val x = 3 } </code></pre> <p>This allows me to invoke <code>X.y()</code> at the end, when <em>all</em> variables are available. But the disadvantage is, the <em>"ugliness"</em>, no domain-user will understand this kind of magic! The domain user must write something like this (but it works!):</p> <pre><code>++ txt (() =&gt; s""" Lorem ipsum Abb. ${Main.fig.number} dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. """) </code></pre> <p>So the idea is to move the closure magic into my DSL api, but therefore I need to pass <code>"$x with reverse reference"</code> as ordinary <code>String</code> and resolve this String at the end as <code>StringContext</code> (s"..."), which resolves the <code>$</code>-references. But so far I found nothing, how to cast this. In short how can I cast <code>"foo $x bar</code> to <code>s"foo $x bar"</code>?</p> <p>What I <a href="http://dcsobral.blogspot.co.uk/2012/01/string-interpolation-on-scala-210.html" rel="nofollow">found</a> is, how to individualize <code>StringContext</code>, but don't know how I can use this for my problem:</p> <pre><code>scala&gt; case class StringContext(parts: String*) { | def rr (args: Any*) = scala.StringContext(parts: _*).s(args: _*) | } defined class StringContext scala&gt; rr"hi" res3: String = hi scala&gt; rr"hi $s" res4: String = hi 1 </code></pre> <p>The other idea is a less "noisy" lambda notation, but how can I write something like (or similar) this:</p> <pre><code>++ txt =&gt; s"""... ${Main.fig.number} ...""" </code></pre> <p>Such a notation would be reasonable. I don't necessarily to write my own String parser with reference resolving. Anybody an sneaky idea?</p> <p>The DSL api is semantically built like this:</p> <pre><code>object ++ { def txt (s: String) = ... } </code></pre>
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    1. COwhat if you define `y` as lazy? `lazy val y = s"$x with reverse reference"`
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    2. CO"I can write x as lazy val, but the compiler moves x and makes it for y available. But for my DSL design the order of y and x must be preserved!"
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    3. COSorry, I didn't get that you meant ordering in the bytecode
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