modelsim compiling error:external function 'xxxxx' may not be used in a constant expr

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You still have typos. This works for me after replacing end with endinterface.

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Thank you for your patiently replying, At last I found the reason why it didn't work in my design is:

one of the functions in the package had declared a local variable without "static" or "automatic" prefix word. But the error message is suppressable for modelsim and is not reported with red color. So this key error message is covered by the following less important red color messages and ignored by me.

Now After add a "automatic" prefix for that local variable, the problem has been solved. Thank you for your patient replying again!