[R] extract R code from Sweave file

[Aimin Yan]

I want to extract all chunk codes from file" 557_project.Rnw". why this is 
not ok?

thanks,

Aimin

 > Rtangle("557_project.Rnw",output="557_project")
Error in Rtangle("557_project.Rnw", output = "557_project") :
         unused argument(s) ("557_project.Rnw", output = "557_project")