These are just two functions that wrap and unwrap a string. Your "type" doesn't generate a compile-time error when constructed with the wrong data. This doesn't even handle the simplest use case:
putStrLn (toString (fromString "something."))Not to mention that to be truly useful a static type would need some sort of literal that would emit a compile-time error if the supplied init data was wrong.
In short, examples above do not demonstrate Haskell's ability to statically enforce rules like "string needs to end with a dot".
Now, you could make a type that always prepends a dot when asked for a string representation, which happens to enforce this specific constraint, but you cannot use a trick like this for most constraints (such as the second example of "only alpha characters").