I’m unclear on how conformers are intended to be used.

I’ve seen cases like: - converting a string into a seq so spec regex operators can validate a string - converting a string into an int - converting a string into a UUID

But from my understanding of https://dev.clojure.org/jira/browse/CLJ-2116, conformers aren’t intended to be used for transformation

Are the above cases unintended uses of conformers? What would be an intended use case? I ask because I’m trying to figure out how to include support for conformers in Expound

to give you information about what you are validating for reuse "later", this makes more sense in the context of validating/destructuring data passed to a macro such as defn

Do you happen to have an example? My main source of examples of macros specs is https://github.com/clojure/core.specs.alpha, but I don’t see any conformers there

my bad I read conforming and I got carried away

I am guilty of using it for transformation, not sure my example is clean but here you go: we have a dsl a bit like sql for a rule engine, we validate the syntax with spec and use a conformer to spill the ast (parsed form)

@mpenet Hm, that is interesting. Is the DSL originally a string then? Do you use spec to parse the string?

also guilty of using it do to json transforms, "old" stuff

yes

the spec is basically a conformer that wraps the parse fn

Right

in reality it s a lot hairier because we have custom explain and whatnot but that s the idea

I see, thanks for the example. One reason it’s hard to add support for conformers is that a) I’m unclear on the intended use and b) in practice, it seems like they are often uses for transformation. I’m not sure if it’s practical to not support a common use case.

Right

it s made for transformations, I guess their validity depends on the context

This is the part I don’t fully understand: conformers do transform values, but what are examples of recommended transformations? @alexmiller said: “I don’t think we are interested in turning spec into a transformation engine via conformers”, but I’m not sure what that includes/excludes

it's a good question indeed

neither the guide or rationale pages mention it

@mpenet In any case, I appreciate you explaining how you use them in practice. This is very helpful for my research, since I may end up wanting to support different use cases

you're welcome. love expound. thanks for that

the guide page intentionally does not mention conformers as we consider them to be primarily useful for writing new custom composite spec types (not for general data transformation)

I think having a tool for transforming data informed by specs would be awesome. I don’t think conformers are that tool.

I'm trying to use spec to document a map that contains a :key-fn that returns a collection i.e. on this data {:aliases #{:bob :robert}}, {:key-fn :aliases} would be suitable. However this happens

(s/def ::key-fn
  (s/fspec :args (s/cat :item any?)
           :ret (s/coll-of any?)))

(s/def ::my-map (s/keys :req [::key-fn]))

(s/valid? ::my-map {::key-fn :aliases}) ;;false
(s/valid? ::key-fn :aliases) ;; false

Is there a way to write a spec that checks properties of pairs of elements in a sequence? E.g. in [{:a 1 :b 2} {:a 2 :b 3} {:a 3 :b 4}] I’d like to check that :b is equal to :a for each pair of items from the sequence.

I can do this as a function on the sequence.

But then on failure explain returns the entire sequence as the value causing the problem.

erm, let me fix that

you can do it but not as a function on the sequence, but each element of it

unless I understand you wrong

Do you mean there is some relationship between adjacent maps? or within individual maps?

I mean that for {:a 1 :b 2} and {:a 2 :b 3} :b of the first and :a of the second must match, and then for {:a 2 :b 3} and {:a 3 :b 4}, we have the same check and so on

gotcha

you have a tradeoff here

You can individually check pairs by running (map #(s/valid? ....) (partition 2 1 collection))

iff you want more targeted error messages

otherwise you can continue to check the whole collection and get errors at the collection level

depends on what you want

ok, thanks, that’s what I thought but wanted to make sure there wasn’t some other way 🙂

I don't believe that (at this time) there is a have-your-cake-and-eat-it-too...