Because + is already taken. The way Haskell has done math operations, using + on strings would mean you'd also have to define - and * and a couple others. edit

Because + is already taken. The way Haskell has done math operations, using + on strings would mean you'd also have to define - and * and a couple others. edit: the confusion on that being a comment is likely due to linewrap issues in the site. That's not a Haskell thing, that's just this person's css.