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

You could think of let as syntactic sugar for creating a new lexical scope with fn then applying it immediately:

(let [a 3 b 7] (* a b))  ; 21
; vs.
((fn [a b] (* a b)) 3 7) ; 21

So you could implement let with a simple macro and fn:

(defmacro fnlet [bindings & body]
  ((fn [pairs]
    `((fn [~@(map first pairs)] ~@body) ~@(map last pairs)))
   (partition 2 bindings)))

(fnlet [a 3 b 7] (* a b)) ; 21