Question

I have two somewhat related problems, shown by the following:

user=> (if (symbol? 5) (meta (var 5)) 5)
CompilerException java.lang.ClassCastException: java.lang.Long cannot be cast to clojure.lang.Symbol, compiling:(NO_SOURCE_PATH:6) 
user=> (defn dometa [x] (if (symbol? x) (meta (var x)) x))
CompilerException java.lang.RuntimeException: Unable to resolve var: x in this context, compiling:(NO_SOURCE_PATH:7) 
user=> 

In the first case, since 5 is not a symbol I would not expect (meta (var 5)) to be evaluated, but it is (or at least that’s the way it seems to me).

In the second case, if I want to place the first expression in a function, and parameterize the value being tested, the (var …) function no longer works.

Answer 1

The Var object is looked up at compile time. For the behaviour I’m inferring from your examples, you should use find-var.

user=> (if (symbol? 5) (meta (find-var 5)) 5)
5
user=> (defn dometa [x] (if (symbol? x) (meta (find-var x)) x))
#'user/dometa