I noted the in first example in the linked into - Python:

    def square(n):
      return n * n

Pyret:

    fun square(n :: Number) -> Number:
      n * n
    end

there's extra stuff. It also kind of loses the elegance of Python reading close to normal language - if you don't know programing but can do math you'd figure the first was define a function that gives a square but be confused what (n :: Number) -> Number: was about.