code: func newInvocation(name string, def ast.Node, fn Symbol, args []Symbol) *Invocation {
  	return &Invocation{
  		symbol: symbol{
  			name: name,
  			def:  def,
  		},
  		fn:   fn,
  		args: args,
  	}
  }
docs: // newInvocation returns a new Invocation symbol.