On Sun, Feb 27, 2011 at 2:10 PM, Ken Wesson <kwess...@gmail.com> wrote:
> On Sat, Feb 26, 2011 at 8:14 PM, Mark <markaddle...@gmail.com> wrote:
>> I get this:
>> #<CompilerException java.lang.IllegalArgumentException: Wrong number
>> of args (3) passed to: Symbol (C:\Users\addma03\workspace\test\src\main
>> \clojure:1)>
>>
>> A few suggestions:
>> 1) An improved line number
>> 2) I'd like to see the value of the Symbol
>> 3) I'd like to see the three args applies to the symbol and, if the
>> symbol resolves to a function, I'd like to see the arity of the
>> function.
>>
>> Something like:
>> Wrong number of args (3) passed to Symbol 'some-fn' which expects
>> arity 2
>
> This is interesting. I just checked with my copy of 1.2 and it seems
> you can indeed call a symbol as a function. It appears to try to look
> itself up in its first argument, the same as a keyword, and if not
> found or the first argument is not a map returns the (optional) second
> argument:
>
> user=> ('+ {'+ 3 '* 4} 42)
> 3
> user=> ('+ {'- 3 '* 4} 42)
> 42
>
> Of course this is rather icky to use because of the need to quote the symbols.
>
> So, the arity expected by a function like + ends up irrelevant. If you
> invoke something on '+ it wants either one or two arguments.
>
> If you're seeing this error you probably have a buggy macro that's not
> unquoting something as many times as it should be. Quoting-depth
> errors (other than forgetting to unquote something at all) seem to be
> most common when writing macros that emit other macros, and ending up
> with nested syntax-quoted expressions, doubled-up ~~@foo type
> unquotings, and things like `(quote ~foo) in helper functions.
>
> If the error points to a macro invocation I'd suggest inspecting the
> output of (macroexpand-1 '(the-problem-invocation)) and seeing what
> you get. If the output contains quoted symbols in operator position
> that clearly are meant to be just normal calls to functions then
> you've at least determined that the problem is caused by the macro.
> Though it could be the case that your arguments to the macro violate
> its preconditions. If it's not your own macro, check its
> documentation. If it is it has a bug since it's not doing what you
> want it to do and it's yours. If it's not it may or may not have a
> bug.
Addendum: the most likely macro *argument* error to cause this is
quoting a function name macro argument that you shouldn't be quoting,
e.g. (the-macro 'my-func ...) instead of (the-macro my-func ...). The
macro just plops (quote my-func) wherever it should put my-func and
boom!
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