What does t0,t1,t2 and a0 mean in Haskell?

Question

I have been coding in Haskell for couple of weeks now and I keep on seeing errors with t0,t1,t2 and a0. I'm wondering, do they have any in particular meaning or they are just variables? I am asking because I would like to understand better the errors that the compiler spits at me.

Answer 1

No, they do not have any particular meaning. They're just variables denoting arbitrary type, as you have noticed. The numbering of these variables (t0, t1, t2 etc.) is related to typechecking process internals and also does not mean anything in particular, as far as I know.