I have studied Haskell in college, and it was certainly different. I actually had no understanding of what map
was doing in Perl until I saw some Haskell. The line between theoretical and practical knowledge is not one that I could draw.
I think Perl is more similar to Ruby than it is to Haskell in some ways, but I think the difference between Perl and Ruby is still significant. The idioms, the philosophy, the approach to solving problems, those things are significantly different in Perl and Ruby. You could say there's little difference between the syntax of C and Perl, but even though I can write Perl that looks very much like C, I certainly don't. I don't think Ruby people write Ruby that looks like Perl either.
I'd say learning Ruby if you already know Perl is like learning German if you already know English. Learning Haskell when you know Perl is like learning Japanese when you know English. (The analogy likely doesn't make sense unless you've studied all three of those, but anyways...) There can be benefit in both.
It's something to think about. I will consider diving into Haskell again. (I still have nightmares from last time though.)