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    <p>I have a hard time understanding what you're trying to achieve, and why you are using Trees everywhere. Trees are really low level, hard to use, tricky, and it is very difficult to understand what the code does. Quasiquotes (<a href="http://docs.scala-lang.org/overviews/macros/quasiquotes.html" rel="nofollow">http://docs.scala-lang.org/overviews/macros/quasiquotes.html</a>) are the way to go indeed and you can use them on scala 2.10.x production release thanks to the macro paradise plugin (<a href="http://docs.scala-lang.org/overviews/macros/paradise.html" rel="nofollow">http://docs.scala-lang.org/overviews/macros/paradise.html</a>). The you can simply write <code>q"(a: Int) =&gt; {val z = "toShort"; a.z}"</code> and you directly get the tree expression you just typed.</p> <p>To answer your question, the first point is to remember that macros are evaluated at compile time. They therefore can not generate code which depends on a runtime value. This is why the compiler is complaining about your <code>splice</code>. But if you pass a value which can be computed at compile time, typically a literal, then you can use eval to get its value within your macro code. Eval does suffer a bug though, as indicated in scaladoc. It should only be called on untyped trees. So the way to call eval on an <code>s: c.Expr[String]</code> expression would be <code>val s2 = c.eval(c.Expr[String](c.resetAllAttrs(c.tree.duplicate)))</code> which gives you a <code>String</code> you can then use normally in your code, for instance <code>q"(a: Int) =&gt; a.${newTermName(s2)}"</code>.</p> <p>To put it all together, let's imagine you to create a macro that'll output a string value from an object and one of its <code>String</code> field. It'll give something like</p> <pre><code>def attr[A](a: A, field: String): String = macro attrImpl[A] def attrImpl[A: c.WeakTypeTag](c: Context)(a: c.Expr[A], field: c.Expr[String]) = { import c.universe._ val s = c.eval(c.Expr[String](c.resetAllAttrs(field.tree.duplicate))) c.Expr[String](q"a.${newTermName(s)}") } </code></pre> <p>REPL session test:</p> <pre><code>scala&gt; object a { val field1 = "field1"; val field2 = "field2" } defined module a scala&gt; attr(a, "field1") res0: String = field1 scala&gt; attr(a, "field2") res1: String = field2 </code></pre> <p>To understand the difference between compile time and runtime, you can meditate about the following result in REPL ;-)</p> <pre><code>scala&gt; val s = "field1"; attr(a, s) error: exception during macro expansion: scala.tools.reflect.ToolBoxError: reflective compilation has failed: $iw is not an enclosing class at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal.throwIfErrors(ToolBoxFactory.scala:311) at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal.compile(ToolBoxFactory.scala:244) at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl.compile(ToolBoxFactory.scala:408) at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl.eval(ToolBoxFactory.scala:411) at scala.reflect.macros.runtime.Evals$class.eval(Evals.scala:16) at scala.reflect.macros.runtime.Context.eval(Context.scala:6) at .attrImpl(&lt;console&gt;:14) scala&gt; val s = "field1" s: String = field1 scala&gt; attr(a, s) res3: String = field1 </code></pre> <p>Hope it helps ;))</p>
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    1. COThanks for the answer! Probably quasiquotes is the way to go but it is available on scala 2.11 which is not official yet. I've put a.z with z being a value defined inside the function to be available at compile time avoiding runtime values. Could you extend your answer with a possible solution of this example? `c.eval(c.Expr[String](Select(Ident(newTermName("z")))))` does not work :\. Take a look to the gist at line 197.
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    2. COYou can use macro paradise plugin, which includes quasiquotes, on 2.10.x production release as described in http://docs.scala-lang.org/overviews/macros/paradise.html
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    3. COThanks again, I thought that they are available just in 2.11... Do you known why `c.Expr[Unit](q"""println("hello world!")""")` just works and `c.Expr[Int => Short](q"""(a: Int) => a.toShort""")` does not? This error was thrown :\ (`scala: Unable to read an event from: rO0ABXNyADlvcmcuamV0YnJhaW5zLmpwcy5pbmNyZW1lbnRhbC... Error: Unknown source file: embeddedFile--QuasiquoteCompat.scala@36a12aaa83f74d5b8ce323d542d159c0 java.lang.RuntimeException: Unknown source file: embeddedFile--QuasiquoteCompat.scala@36a12aaa83f74d5b8ce323d542d159c0`
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