Clojure wat

wat.clj

user=> (def bs '[a 1 b 2])
#'user/bs
user=> (type bs)
clojure.lang.PersistentVector
user=> (vector? bs)
true
user=> (let bs (+ a b))
java.lang.IllegalArgumentException: let requires a vector for its binding (NO_SOURCE_FILE:0)

I know you're clear on what's going on here, but I think it's interesting how many different meanings bs has here.

(def <a var with name the symbol bs> '[a 1 b 2])

(type <the value bound to the var named by the symbol bs>)

(vector? <the value bound to the var named by the symbol bs>)

(let <the symbol bs> (+ a b))

and the error would be a lot clearer if it said:

let requires a vector literal as its first argument, found a symbol: bs

Yeah, and for someone "in the know" it is trivial to demonstrate what happened:

user=> (defmacro foo [thingy] (type thingy))
#'user/foo
user=> (foo bs)
clojure.lang.Symbol

But this sort of thing can be so bewildering to fresh clojure programmers, and the error is effectively telling you to do exactly what you did, as far as a naive inspection might discover.

It makes me feel bad for the newbies :)