This may sound (and probably is) quite superficial, but I am immediately put off by any language that uses syntax like this: foldr' (+) :: Num t1 => t1 -> [t1] -> t1
Why? Because of things like => and -> are just a pain to write all the time and make you chase all over the keyboard, even more so on non-english keyboards. Just my very personal preference of course, but still...
It is quite superficial. Code being easy to read is much more important than code being easy to write. I'm not saying it's a bad idea to have both, but look at Java or C# that are a pain to write without a very smart IDE (just because of the amount of boilerplate). Even they have been saved by tooling.
Also, modern popular languages tend to use arrows (Java, C#, ES6). Not to say that popularity matters, but people are used to it nowadays.
