A question that a Stack Overflow user emailed to me:
I have the below function:
(defn partial-or-fill-at-test? [price] (if (partial-or-fill-at? price) true (do (println "WRONG PRICE") false)))I get the below error when I use it:
java.lang.ClassCastException: java.lang.Boolean cannot be cast to clojure.lang.IFnI want to it to print something when the result of that predicate is false. Any help will do.
The problem is somewhere in your definition of partial-or-fill-at?. If I try a simple definition of partial-or-fill-at? as as function, everything works:
(defn partial-or-fill-at? [price] (> price 100))
(defn partial-or-fill-at-test? [price]
(if (partial-or-fill-at? price) true (do (println "WRONG PRICE") false)))
user=> (partial-or-fill-at-test? 200)
true
user=> (partial-or-fill-at-test? 50)
WRONG PRICE
false
The error message java.lang.Boolean cannot be cast to clojure.lang.IFn means that somewhere, you have a Boolean (true or false) that is trying to used as an IFn (Clojure’s name for a function).
The true and false literals in your code are being used as values, not functions, so that is not the problem. The only place where a boolean could be used like a function is partial-or-fill-at?. If you defined it with a boolean value, using def instead of defn, you would get this error. For example, perhaps you accidentally wrote this:
; earlier in the code
(def price 500)
; …
(def partial-or-fill-at? (> price 100))
when you meant this:
(defn partial-or-fill-at? [price] (> price 100))
Inspect your definition of partial-or-fill-at? – also making sure that all parentheses balance and that the definition covers the section of code you expect it to – and figure out how to change its value from a boolean to a function.
partial-or-fill-at? Otherwise it's impossible to know what's wrong.partial-or-fill-at?, then please edit this question to include the code for that function.