when OO is wrong

[Alexy Khrabrov <deliverable@gmail.com>]

I liked the part of Yaron's Caml Trading talk where he says that OO is  
not always the right way to model things.  I wonder about other  
situations where OO is wrong and functional approach simplifies  
modeling?  And then, since UML is so OO-motivated, should we get a new  
UML, or all that OO Analysis/Design/Development is a heritage of non- 
programming bureaucracy?

I've done some Fortran coding recently for high-performance, numeric  
OpenMP app, and also noticed that just about everything fits into an  
array -- just like almost anything in FP fits into a list.  That's  
another case where a flat structure clears the mind.  I've found a  
graph library in Fortran 77 which, with its compact representation,  
was directly applicable to a rather complex social network modeling  
problem of today!  There's something similar to the "everything is  
array" simplification in FP, but it's hard to pin it down exactly.

What is it about FP which makes modeling simpler than OO, conceptually  
and technically?  How can folks summarize their "enlightenment"  
experiences in this regard?

Cheers,
Alexy