Comments on: Scala: 99 problems

By: My Software Development journey: Year 3-4 at Mark Needham

My Software Development journey: Year 3-4 at Mark Needham — Mon, 05 Oct 2009 08:54:09 +0000

[...] recently Liz and I have been playing around with Scala and from trying out some of these exercises I am seeing that when writing recursive functions my [...]

By: Mark Needham

Mark Needham — Thu, 01 Oct 2009 08:09:48 +0000

@Raphael – man I always spot the tail recursion but I missed this one! Good point.

@Charlie – that solution reads quite well. I think it’s possible to do a solution using the built in function ‘flatMap’ which would make it even more concise.

By: Charlie Knudsen

Charlie Knudsen — Thu, 01 Oct 2009 02:02:38 +0000

I am still trying to wrap my head around functional programming in general. I find the below solution to make the most sense to me:

def flatten[A](list : List[A]) : List[A] = {
list.foldRight(Nil:List[A])((elem, start:List[A]) => {
elem match {
case x:List[A] => flatten(x) ::: start
case _ => elem :: start
}
}
)
}

By: Raphael Speyer

Raphael Speyer — Wed, 30 Sep 2009 22:59:09 +0000

FWIW the second option is tail recursive, so it can deal with indefinitely long lists, whereas the third option will stack overflow given a long enough input.

By: Mark Needham

Mark Needham — Wed, 30 Sep 2009 20:07:31 +0000

@Hector – yeh that’s a good point. I think that’s probably a hang over from the fact that in the previous problems ‘A’ could be a specific type but you’re right for this problem it’s irrelevant.

@Oli – looking at the Prolog problems reminds me of university days!

By: Oli

Oli — Wed, 30 Sep 2009 16:46:43 +0000

Hehe “not quite intuitive” that’s the word,
“the solution is cleaner and easier to read” that’s the message.

I never thought I would dig up my old Prolog assignments and fundamental scripts (#07) from https://prof.ti.bfh.ch/hew1/informatik3/prolog/p-99/

Thank you for keeping me hooked on Scala!

By: Hector Chu

Hector Chu — Wed, 30 Sep 2009 16:19:41 +0000

Is there any point in the type parameter A, as it will nearly always be deduced as type Any?