Question

We have a simple function definition:

(defn calculate [d x y]
  ((if (and (== d 1) (== x 1) (== y 0))
     1
     0)))
(println (calculate 1 1 0))

But that results in this error:

Exception in thread "main" java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke    (DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:616)
    at jline.ConsoleRunner.main(ConsoleRunner.java:69)
Caused by: java.lang.ClassCastException: java.lang.Long cannot be cast to clojure.lang.IFn
    at user$calculate.invoke(main.clj:13)
    at user$eval5.invoke(main.clj:17)
    at clojure.lang.Compiler.eval(Compiler.java:6465)
    at clojure.lang.Compiler.load(Compiler.java:6902)
    at clojure.lang.Compiler.loadFile(Compiler.java:6863)
    at clojure.main$load_script.invoke(main.clj:282)
    at clojure.main$script_opt.invoke(main.clj:342)
    at clojure.main$main.doInvoke(main.clj:426)
    at clojure.lang.RestFn.invoke(RestFn.java:408)
    at clojure.lang.Var.invoke(Var.java:401)
    at clojure.lang.AFn.applyToHelper(AFn.java:161)
    at clojure.lang.Var.applyTo(Var.java:518)
    at clojure.main.main(main.java:37)
    ... 5 more

(BTW, line 13 is the line with if and and).

The same with vectors:

(defn calculate [vectorr]
  ((if (and (== (vectorr 0) 1) (== (vectorr 1) 1) (== (vectorr 2) 0))
     1
     0)))
(println (calculate [1 1 0]))

This results in:

Caused by: java.lang.ClassCastException: java.lang.Long cannot be cast to clojure.lang.IFn

… the same.

And with a map:

(defn calculate [mapp]
  ((if (and (== (mapp :d) 1) (== (mapp :x) 1) (== (mapp :y) 0))
     1
     0)))
(println (calculate {:d 1 :x 1 :y 0}))

Results in the same message:

Caused by: java.lang.ClassCastException: java.lang.Long cannot be cast to clojure.lang.IFn

We think is has something to do with if, or the comparisons. We have tried it with normal arguments, a vector as an argument and with a map as such and obviously, the error stays the same.

We’ve also tried many other variations without greater insights on the actual problem.

Answer 1

You have an extra pair of parentheses around your function body, which means you want to call the result of the if (which is either 1 or 0 — i.e. a long).

It should be:

(defn calculate [vectorr]
  (if (and (== (vectorr 0) 1) (== (vectorr 1) 1) (== (vectorr 2) 0))
     1
     0))