New to Groovy - question on code in documentation

[Les Hartzman]

Hi,

As the subject says, I’ve just gotten started with learning Groovy and have 
been going through the documentation.

There is some code in the section on files that is not explained. If someone 
could clarify that, it would be great:

 doInTmpDir { b ->
                File file = null
                def tmpDir = b.tmp {
                    file = 'foo.tmp'('foo')
            }
What does ‘foo.tmp’(‘foo’) do?
I tried to put this into groovysh but it complained:  No signature of method: 
groovysh_evaluate.foo.tmp() is applicable for argument types: 
(java.lang.String) values: [foo]

Thanks in advance.
Les