Loading Files from a Directory in Haskell
The loadData function looks just fine to me. I don't see a way it could be any more elegant given what it's doing. I do actually like the way you have separated reading the file and parsing it. That's the way to go. 

Your concern about "avoiding the IO monad" shouldn't be a concern. On the contrary, that's actually a "best practice", known as "pushing I/O to the boundary". It means that the majority of your program should be pure, and only a thin shell should deal with external world. This way you can easily test and debug the majority of your program.

The only thing I might do is make the last three lines one expression:

traverse readFile prefixed
  &lt;&amp;&gt; map parseTsv
  &lt;&amp;&gt; zip filtered


I find this a bit more readable, but that's just a matter of personal taste.



But the parseLine function could sure use some improvement.

First, the control flow. Look what it's doing: compute a Maybe value, then if it's Just, compute another Maybe value from its contents. That's exactly what "bind" does! This means it can be nicely represented as a do block.

Second, read is a partial function. This means it can fail at runtime if there is a non-number in the file. I understand this probably Should Never Happen™, but you'd be surprised how many things that "should never happen" do, in fact, happen all the time. :-)

But since you're already in the Maybe context, it would be easy to use readMaybe instead, and skip the malformed numbers.

Applying both points:

parseLine line = do
    i &lt;- elemIndex '\t' line
    let (word, strCount) = splitAt i line
    count &lt;- readMaybe strCount
    return (word, count)