Clojure PN (java.lang.ClassCastException)

Question

I'm using Clojure for a code golf challenge, in which the aim is to write a function that evaluates and returns the value from a Polish Notation expression. Below is my code.

(require '[clojure.string :as s])
(defn p[e](
    (load-string (reduce (fn[x c] 
        (s/replace x #"([\+\-\*\/] (\(.*\) \d+|\d+ \d+))" "($0)")
    ) e (subvec (s/split e #"\d") 1)))))

Remember this is golfed code (not meant to be readable).

In short, the function takes a string, the string is then split into a vector. Reduce iterates over the vector and applies the expression for the n-1 elements in the vector. What comes out is a string that Clojure should be able to evaluate with load-string.

If I declare a var called e with the value "+ 3 5" then run just the reduce from the function, "(+ 3 5)" is expected as returned. But when I call the function as (p "+ 3 5") I get the following error.

java.lang.ClassCastException: java.lang.String cannot be cast to clojure.lang.IFn (NO_SOURCE_FILE:0)

No idea what's going on here.

Answer 1

You are using extra parentheses after defn args vector. It should be:

(defn r[e]
  (load-string 
    (reduce 
      (fn[x c] 
        (s/replace x #"([\+\-\*\/] (\(.*\) \d+|\d+ \d+))" "($0)")) 
      e 
      (subvec (s/split e #"\d") 1))))

user=> (r "+ 3 5")
8