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POScala Macros: Convert/parse a Tree to a Name
 

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  1. POScala Macros: Convert/parse a Tree to a Name
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    <p>This is a simplified example but the problem remains the same.</p> <p>I want to achieve this using macros (scala based pseudocode):</p> <pre><code>(a: Int) =&gt; { val z = "toShort" a.z } </code></pre> <p>If I reify it, I would obtain something similar to this:</p> <pre><code>Function( List( ValDef( Modifiers(Flag.PARAM), newTermName("a"), Ident(scala.Int), EmptyTree ) ), Block( List( ValDef( Modifiers(), newTermName("z"), TypeTree(), Literal(Constant("toShort")) ) ), Apply( Select( Ident(newTermName("a")), newTermName("toShort") ), List() ) ) ) </code></pre> <p>I dont know how to access to a value and then use it as a TermName.</p> <p>I tried replacing <code>newTermName("toShort")</code> with <code>newTermName(c.Expr[String](Select(Ident(newTermName("z")))).splice)</code> but the compiler doesn't seem to like:</p> <blockquote> <p>exception during macro expansion: java.lang.UnsupportedOperationException: the function you're calling has not been spliced by > the compiler. this means there is a cross-stage evaluation involved, and it needs to be invoked explicitly. if you're sure this is not an oversight, add scala-compiler.jar to the classpath, import <code>scala.tools.reflect.Eval</code> and call <code>&lt;your expr&gt;.eval</code> instead.</p> </blockquote> <p>I've also tried 'eval' as suggested by compiler: <code>newTermName(c.eval(c.Expr[String](...))</code> but neither worked.</p> <p>How could I convert a tree like <code>Select(Ident(newTermName("z")))</code> (which is a access to a value of a local val) to <strike>a Name</strike> a string which can be used as a parameter for <code>newTermName</code>? Is it possible?</p> <p><strong>UPDATE:</strong></p> <p>Here the real problem brought to you as a <a href="https://gist.github.com/glerchundi/b5c0fef88fb0bb222fde#file-validation-scala-L196" rel="nofollow">gist</a>!</p> <p>Thanks in advance,</p>
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    1. PO
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      1. PTAnswer
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    1. PTQuestion
    1. USGorka Lerchundi Osa
    1. USGorka Lerchundi Osa
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      1. POScala Macros: Convert/parse a Tree to a Name
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    1. CO`newTermName("z")` already returns a `Name`. I don't understand what is wrong with that one.
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      1. POScala Macros: Convert/parse a Tree to a Name
      1. USkiritsuku
    2. CODo you mean you want to extract it from an existing Tree? Like `val Select(Ident(name)) = tree`?
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      1. POScala Macros: Convert/parse a Tree to a Name
      1. USkiritsuku
    3. COI want to use the value of `val z` to be the param of `newTermName` method. `Select(Ident(newTermName("z")))` is the access to the value and then: `newTermName("<value of z>")`. So it would be possible to do: `a.toShort`.
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      1. POScala Macros: Convert/parse a Tree to a Name
      1. USGorka Lerchundi Osa
 

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