Scala Match Error during macro expansion - scala

Question

Hi I am trying to convert mathematical expressions into the Binary expressions.
e.g;
2 + x turns into BinOp("+",Number(2.0),Var(x))
I want to make those during the compile time so I used macros in scala. Here is my macro implementation;
class ExpressionImplicitsImpl(val c: Context) {
def expr(exprTree: c.Expr[AnyRef]) : c.Expr[Expression] = {
import c.universe._
exprTree.tree match {
case Ident(TermName(x)) => reify{Var(x.toString)}
case Literal(Constant(a)) => reify{Number(a.asInstanceOf[Double])}
case q"$a + $b" => reify{BinOp("+", expr(a.asInstanceOf).splice, expr(b.asInstanceOf).splice)}
case q"$a * $b" => reify{BinOp("*", expr(a.asInstanceOf).splice, expr(b.asInstanceOf).splice)}
}
}
}
BinOp, Var and Number classes are case classes and extends Expression class. But this is not so important in that case.
My actual class which uses this macro is
def main(args: Array[String]) {
import ExpressionImplicits._
val e1 = expr { (x: Double) => (x * 6) + (8.0 * x) }
println(e1) // I expect BinOp(+,BinOp(*,Var(x),Number(6.0)),BinOp(*,Number(8.0),Var(x)))
}
However, I get a matching error. I am kind of new pattern matching and this is my second macro trial. So if you could give me educative examples and simple explanations would be great.