Better handling of calling a non-function

src/babashka/interpreter.clj

@@ -160,6 +160,10 @@
 
 (define-lookup)
 
+(defmacro one-of [x elements]
+  `(let [x# ~x]
+     (case x# (~@elements) x# nil)))
+
 (defn resolve-symbol [expr]
   (let [n (name expr)]
     (if (str/starts-with? n "'")
@@ -180,6 +184,8 @@
       (into (empty expr) (map i expr))
       (seq? expr)
       (if-let [f (first expr)]
+        (let [f (or (one-of f [if when and or -> ->>])
+                    (interpret f in))]
           (if-let [v (var-lookup f)]
             (apply-fn v i (rest expr))
             (case f
@@ -204,7 +210,7 @@
                     (apply-fn (resolve-symbol f) i (rest expr))
                     (ifn? f)
                     (apply-fn f i (rest expr))
-                  :else nil)))
+                    :else (throw (Exception. (format "Cannot call %s as a function." (pr-str f))))))))
         expr)
       ;; read fn passed as higher order fn, still needs input
       (-> expr meta ::fn)