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adding test function to a variable
Function documentation is internally set like the above: <i>defn</i> is a macro that defines a function and puts the second argument as the doc string of the variable that points to the function body (among many other things).
<h4>Adding a test function to a variable</h4>
We first declare the variable, and then define it with a metadata map that includes a test function:
<source lang="lisp">
(declare a)
(def
#^{:test #(if (< a 10) (throw (Exception. "Value under 10!")))}
a 6)
</source>
... which we then test, by invoking the function <i>test</i> not on the value of the variable <i>a</i> (which could have its own metadata map), but on the variable <i>a</i> itself, referred to with the <i>#'a</i>:
<source lang="lisp">
(test #'a)
</source>
The test results, in this case, in an exception being thrown:
java.lang.Exception: Value under 10!
Otherwise, it would just return the <i>:ok</i> keyword.
<h3>A fibonacci sequence: lazy and infinite sequences</h3>