In Rob's post, he uses some sample code that calculates batting averages and standings for baseball teams. His Clojure code begins with the namespace directive "(ns one)", which tells the Clojure compiler into which namespace to register these functions. When testing out his code, I created a project named Baseball, which creates a file called baseball.clj:
When I tried to build and run his code, I got the following error:
And got this:
Not very helpful. But when I clicked View Detail, I was presented with both an error message and, more usefully, a stacktrace:
Here is the stacktrace in full:
at
clojure/core$fn__13329$throw_if__13331.__invokeHelper_2v(clojure/core$fn__13329$throw_if__13331_base
this, Object pred, Object fmt, Object args) in core.clj:line 4684
at clojure/core$fn__13329$throw_if__13331.doInvoke(Object , Object , Object )
at clojure/core$fn__13368$load_one__13370.__invokeHelper_3(clojure/core$fn__13368$load_one__13370_base this, Object lib, Object need_ns, Object require) in core.clj:line 4732
at clojure/core$fn__13368$load_one__13370.invoke(Object , Object , Object )
at clojure/core$fn__13461$compile__13463.__invokeHelper_1(clojure/core$fn__13461$compile__13463_base this, Object lib) in core.clj:line 4916
at clojure/core$fn__13461$compile__13463.invoke(Object )
at clojure.lang.Var.invoke(Object arg1)
at BootstrapCompile.Compile.Main(String[] args)
at clojure/core$fn__13329$throw_if__13331.doInvoke(Object , Object , Object )
at clojure/core$fn__13368$load_one__13370.__invokeHelper_3(clojure/core$fn__13368$load_one__13370_base this, Object lib, Object need_ns, Object require) in core.clj:line 4732
at clojure/core$fn__13368$load_one__13370.invoke(Object , Object , Object )
at clojure/core$fn__13461$compile__13463.__invokeHelper_1(clojure/core$fn__13461$compile__13463_base this, Object lib) in core.clj:line 4916
at clojure/core$fn__13461$compile__13463.invoke(Object )
at clojure.lang.Var.invoke(Object arg1)
at BootstrapCompile.Compile.Main(String[] args)
Now I was getting somewhere: The highlighted lines were the call just before the error was thrown, so by looking there I should be able to get some idea of what went wrong. So I re-ran the program and this time chose to open a new instance of Visual Studio. I was asked to supply the source code for the lines I was debugging. Fortunately, the Find Source dialog started me out just one folder away from the source by default, in C:\Users\daniel_cotter\AppData\Local\Microsoft\VisualStudio\10.0\Extensions\jmis\vsClojure\1.1.0\Runtimes\1.2.0:
I chose clj-source and was presented with this much more helpful view (I've skipped to line 4732, where the error was thrown:
Summary
The lesson I'm taking from all this? Be careful with your namespaces. For those of us accustomed to .NET's liberal namespacing conventions (basically, a namespace block is all you need, and it doesn't have to the filename), Java's conventions are much stricter, and Clojure seems to follow suit, even when in a .NET environment. Personally, I have long found namespacing issues one of the more confusing parts of Clojure, probably because I am not well-versed in Java.
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