If you are curious about the types inferred by ClojureScript, it is easy to get some insight using a macro:
(defmacro inferred-type [form]
`'~(cljs.analyzer/infer-tag &env
(cljs.analyzer/no-warn (cljs.analyzer/analyze &env form))))This is the kind of dev-time macro you could refer using the new user.cljs feature.
This gist sets this macro up along with a REPL, running in a branch of ClojureScript containing all of the in-flight type inference revisions:
clj -Srepro -Sdeps '{:deps {github-mfikes/gist-3837f510aad3e8ff766eb9071ef66b2b {:git/url "https://gist.github.com/mfikes/3837f510aad3e8ff766eb9071ef66b2b" :sha "ee58ef464e20e482aec4ef0928f4e61a9ddc77de"}}}' -m cljs.main -co @compile-opts.edn -re node -r
Here is an example of using it:
cljs.user=> (inferred-type 1)
number
cljs.user=> (inferred-type "a")
string
cljs.user=> (inferred-type (if x 1 "a"))
#{number string}
Checking an inferred type inside an expression:
cljs.user=> (let [x (+ 2 3)]
(inferred-type x))
number
You can even see the new function return type inference in action:
cljs.user=> (defn foo [x]
(cond
(pos? x) "a"
(neg? x) 3
:else true))
#'cljs.user/foo
cljs.user=> (inferred-type (foo 1))
#{boolean number string}
Inferred types for if expressions
cljs.user=> (inferred-type (if "a" 1 :kw))
number
and the implications for and / or:
cljs.user=> (inferred-type (or nil 1 "a"))
number