[R] calculating IRR (accounting) in R

[paul sorenson]

I am trying to replace a spreadsheet model of a project justification 
with an R script.

I can't seem to track down R functions to calculate Internal Rate of 
Return and NPV?  Am I missing something?  NPV doesn't seem so difficult 
to calculate (at least for a regular series) but I am struggling to 
identify how to solve for IRR in R.

It would be sufficient if it worked for a regular series but really 
useful if there was something that worked with irregular time series.

cheers