let vs def in clojure

Question

I want to make a local instance of a Java Scanner class in a clojure program. Why does this not work:

; gives me:  count not supported on this          


        

Answer 1

LET is not "make a lexical binding in the current scope", but "make a new lexical scope with the following bindings".

(let [s (foo whatever)]
  ;; s is bound here
  )
;; but not here

(def s (foo whatever))
;; s is bound here