query params to Default/Named params, reflection

Trying to find a good approach to map query string params to builder functions using default/named params as in:

def builder = new {
    def apply(
      a:Int = 0,
      b:Int = 0,
      c:Int = 0):String = {
       "a="+a+", b="+b+", c="+c
      }
}

Here is a really clean python example using reflection, see https://gist.github.com/1214994

import inspect 
def call(fun, **myArgs):  names, _, _, values = inspect.getargspec(builder)  defaults = zip(names, values)  valuesToCallWith = dict(defaults + myArgs.items())  return fun(**valuesToCallWith)  
def builder(a = 0, b = 2, c = 3):  return a + b + c
print call(builder, a = 3)           # prints 8print call(builder, b = 9, c = 1)    # prints 10 print call(builder, c = 11)          # prints 13

But without Scala reflection, I may have to pass in a map of values (yuck):

def eval[A](pmap:Map[String,A], pname:String, pdefault:A):A = 
  pmap.get(pname).getOrElse(pdefault)

def builder = new {
    def apply(p:Map[String,Any]):String = {
       "a="+eval(p,"a",0)+
       ", b="+eval(p,"b",2*5)+
       ", c="+eval(p,"c",0)
      }
} 

val abc = Map("a" -> 1, "b" -> 2.3, "c" -> 3)
val ac = Map("a" -> 1, "c" -> 3)
val cFunc = () => 2+5
val af = Map("a" -> 1, "c" -> cFunc())

builder(abc)
builder(ac)
builder(af) 

Any other ideas on how to approach this issue? Thanks!