Recursive clojure.spec doesn't work

[Johan Jonasson]

I might have stumbled upon a bug in clojure.spec, while trying to define a spec. This doesn't compile:

(s/def :html/element

  (s/cat

   :tag keyword?

   :attrs map?

   :children (s/* (s/alt :element (s/spec :html/element)

                         :string  string?))))

The exception says: "Unable to resolve spec: :html/element".

Is it a bug, or is there another way to define this?

[Alex Miller]

s/spec is going to try to resolve that keyword during the definition. Does this do what you want?

(s/def :html/element

  (s/spec (s/cat

                 :tag keyword?

                 :attrs map?

                 :children (s/* (s/alt :element :html/element 

                                               :string string?)))))

[Johan Jonasson]

It works! Thanks! 

Seems like I have to learn more about s/spec.

[Aaron]

I was playing around with something similar to the OP and encountered this same problem using s/spec recursively. Yes, I get it that there are work-arounds, but it seems like this is a legitimate issue. s/spec as you say resolves at definition time, but the rest of the combinators (s/alt, s/and, s/keys, etc.) as far as I can tell are late binding. What's the rationale for s/spec behaving differently? If specs happen to get redefined later this could further complicate matters as everything defined with s/spec will reference the older spec. Why not just make s/spec late binding too and then there would be no such issue with recursive specs?

[Alex Miller]

Can you share a specific case?

[Aaron]

Well I'm referring to the OP's original example:

(s/def :html/element

  (s/cat

   :tag keyword?

   :attrs map?

   :children (s/* (s/alt :element (s/spec :html/element)

                         :string  string?))))

The exception says: "Unable to resolve spec: :html/element".

[Yehonathan Sharvit]

This recursive definition also works - the difference is that the inner :html/element is not wrapped in s/spec:

(s/def :html/element

  (s/cat

    :tag keyword?

    :attrs map?

    :children (s/* (s/alt :element :html/element

                          :string  string?))))

I'm a bit confused about when recursion works and when it doesn't