How to reproduce:
broz@macmicro:~$ grep try ~/.lein/profiles.clj
broz@macmicro:~$ lein try org.clojure/core.typed
nREPL server started on port 56675 on host 127.0.0.1 - nrepl://127.0.0.1:56675
REPL-y 0.3.5, nREPL 0.2.6
Java HotSpot(TM) 64-Bit Server VM 1.8.0_40-b26
Docs: (doc function-name-here)
Source: (source function-name-here)
Javadoc: (javadoc java-object-or-class-here)
Exit: Control+D or (exit) or (quit)
Results: Stored in vars *1, *2, *3, an exception in *e
user=> (require ['clojure.core.typed :as 't])
user=> (t/cf (t/defn repro-core-typed-9 [m :- (t/Seqable String)] (group-by identity m)))
Initializing core.typed ...
Building core.typed base environments ...
Finished building base environments
"Elapsed time: 10484.613659 msecs"
DEPRECATED SYNTAX (NO_SOURCE_PATH): All syntax is deprecated, use clojure.core.typed/All
DEPRECATED SYNTAX (NO_SOURCE_PATH): U syntax is deprecated, use clojure.core.typed/U
Type Error (NO_SOURCE_PATH:1:60) Internal Error (NO_SOURCE_PATH:1:60) Cannot resolve type: Seqable
Hint: Is Seqable in scope?
Hint: Has Seqable's annotation been found via check-ns, cf or typed-deps?
Should not give an internal error.
core.typed rules! I'm finding it very useful for my project and has found many bugs before they hit production--it's a great tool to have access to.