How can I do 'if..else' inside a for-comprehension?

Question

I am asking a very basic question which confused me recently. I want to write a Scala For expression to do something like the following:

for (i <- expr1)         


        

Answer 1

import scalaz._; import Scalaz._

val lhs = (_ : List[X]) collect { case j if j.methodJ => doSomething(j) } 
val rhs = (_ : List[X]) map doSomethingElse
lhs <-: (expr1 partition methodI) :-> rhs