code: func ValueBinder(f func(value string, typ reflect.Type) reflect.Value) func(*Params, string, reflect.Type) reflect.Value {
  	return func(params *Params, name string, typ reflect.Type) reflect.Value {
  		vals, ok := params.Values[name]
  		if !ok || len(vals) == 0 {
  			return reflect.Zero(typ)
  		}
  		return f(vals[0], typ)
  	}
  }
docs: // ValueBinder is adapter for easily making one-key-value binders.