`main` is the entry point of the program. Its type is `IO ()`. It is a warning to omit a type signature in a top level definition, so in a normal program you wo

`main` is the entry point of the program. Its type is `IO ()`. It is a warning to omit a type signature in a top level definition, so in a normal program you would have a `main :: IO ()` type definition. The `IO` allows any kind of effect.