let's talk about qi

https://en.wikipedia.org/wiki/Qi_(programming_language)

Copy pasted example of defining a type for a sorted list.

(12+) (datatype ordering

if (number? X)
if (number? Y)
let Z (* X 2)
if (= Y Z)
__________________
[X Y] : ordering;)
ordering : unit

(13+) [2 3] : ordering
error: type failure

(14+) [2 4] : ordering
[2 4] : ordering

None of the implementations are any good. Once you get them to compile, errors manifest as exceptions in the host language, also everything is shit slow.