They are the arguments of the function, like in any other program (python def f(xs):). But sometimes it is possible to not write them, like here, if we can write the code in pure terms of functions combinations. It's hard to explain clearly (and I'm far from being comfortable in Haskell) but try to practice on easy katas and look at others solutions, try to reuse them... With Haskell installed on your computer you can run a very handy interpreter that allows to do tiny tests easily.

can someone explain this. Very new to haskell.
I am wondering why "xs" or any form of agruement is being used before the equal sign?

so cool!

Really cool approach. It's these kinds of code that made me learn haskell at first. Doing simple things the simple way

No, siempre hay una forma mas redusida jajaj

Elegant.

This seems to be one of, if not the, best soltuions here. Any chance you could write an explanation for us noobs?

Not anymore

Yeah! I was wondering if this could be done without having to destructure the pair... learning so much from everyone here :)

Very Good solution!!!

so Good!!!!!

Nice!

λ> groupCheck "([ab])"
False

this solution not works for there are some other chars in the string. as above.