Replace with-decorator with decorator lists in defn and defclass

[Kodiologist]

• Closes Decorators are ugly #952
• Closes we should have better documentation and error message for with-decorator #1624
• Closes Decorating anonymous functions is inconsistent #2271

I haven't updated the documentation yet.

[Kodiologist]

A possible extension would to make the brackets optional for the common case of only one decorator. However, (defn foo bar [] …) arguably looks like you're defining a function named foo, anyway.

[allison-casey]

Neat!! I'll take a look after work tonight. I do think we should keep the explicit brackets for single decorators. the ambiguity of which is the fn name doesn't seem worth the bracket saving two characters on the brackets.

What is the evaluation order of multiple decorators using the new syntax? Python is right to left/bottom up. Is this the same way?

[Kodiologist]

It should be the same as Python's. I'll tweak a test to make it sensitive to the order in which decorators are called.

[Kodiologist]

And yes, the decorator expressions themselves are evaluated outer-first whereas the functions obtained by this evaluation are called inner-first, in both Python and this Hy implementation. Thus both of these programs print 1 through 4 in order:

def d(n):
   return lambda f: [print(n), f][1]

@[print(1), d(4)][1]
@[print(2), d(3)][1]
def f():
    pass

(defn d [n]
  (fn [f] (print n) f))

(defn
  [(do (print 1) (d 4)) (do (print 2) (d 3))]
  g [])

[allison-casey]

Looks good! just needs documentation updated

[Kodiologist]

Done.