Parentheses are not allowed when sub is called.

The prompt"TestRun cannot continue due to a syntax error "parentheses cannot be used when calling sub.

Solution: Call

Generally, this error occurs when no return value is returned during the call process. It should be said that the call parameter value assignment is incorrect. This error can be solved by calling.

A process call that does not return a value cannot be enclosed in parentheses. Therefore, you should write treesort cat_id and childcount.
If you are not used to it, you can add call to call treesort (cat_id, childcount)
That is to say, parentheses are added when there is a call, and no parentheses are used when there is no call. In addition, a space is required between the function name and parameter.

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However, the call is not required in reference materials, but an error occurs when calling the call without parentheses (invalid characters are prompted). Why?