WIP: :->

[frenchy64]

Introduce a flat syntax for function arguments.

[:-> :any] ; [:=> :cat :any]
[:-> :int :any] ; [:=> [:cat :int] :any]
[:-> [:cat :int] :any]  ; [:=> [:cat [:cat :int]] :any]
[:-> a b c d :any] ; [:=> [:cat a b c d] :any]

;; guard property
[:-> {:fn (fn [[[arg] ret]] ...)}
 :arg :ret]
; [:=> [:cat :arg] :ret [:fn (fn [[[arg] ret]] ...)]]

• disallow :-> without children, looks like an infix op [:=> :a :-> :b].
• test :fn property
• add generators for :ifn :->

[ikitommi]

Thanks! I also too a stab at this earlier. Looking at my stash, the idea was:

• move the malli.util/-util-schema as malli.core/-proxy-schema
• implement :-> using that (you can m/deref to get the underlaying :=> of this)
• there are few places where one needs to check "if the schema is a function schema". There could be a new FunctionSchema protocol or some other & simpler way to tag both variants as valid.
• I just listed both e.g. in :function schema (oh, the crappy name of that!)

-        (when-not (every? #(= :=> (type %)) children)
+        (when-not (every? #(= #{:=> :->} (type %)) children)

the actual :-> impl was:

(defn -->-schema []
  (-proxy-schema {:type :->
                  :fn (fn [p c o] (let [c (map #(schema % o) c), cc [(into [:cat] (butlast c)) (last c)]]
                                    [c (map -form c) (into-schema :=> p cc o)]))}))

not sure if that worked in all possible places, was a quick test, see https://clojurians.slack.com/archives/CLDK6MFMK/p1706446416126059

I think having a new Schema would be simpler here. WDYT?

[ikitommi]

this should be changed too

[ikitommi]

keys with ? in the end should be predicate functions, so flat-arrow would suffice here. https://github.com/bbatsov/clojure-style-guide?tab=readme-ov-file#naming-predicates

[frenchy64]

@ikitommi I took your idea and ran with it. Since you were unhappy with :function, I added a new proxy schema :ifn. LMK what you think.

[:function [:=> [:cat] :int] [:=> [:cat :int] :int]]
==
[:ifn [:-> :int] [:-> :int :int]]