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

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This worked for me going back a number of releases. You have a few typos. Make sure what you posed is exactly what you are compiling.

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Hi, Mr.dave_59.

thanks for replying. I'm sorry that I had not made enough tests. After testing the code I found it worked in module, but not in an interface:

package pkg;
function bit bitgen(int bit1idx);
    automatic bit res = '0;
    if (bit1idx >= 0 && bit1idx < 16)
        res = 1'b1;
    return res;
endfunction
function bit bit2test(bit bits2test);
    if ((bits2test&bitgen(2)) != 0)
        return 1'b1;
    return 1'b0;
endfunction
endpackage
interface iftest# (
    parameter para2test = 15
);
    import pkg::*;
    localparam bit2set_flag = bit2test(para2test);   // modelsim reports compiling error here!
    initial begin
        if (bit2set_flag == 0)
            $error("bit2 of para2test is not set!");
    end
end
module mod2test# (
    parameter para2test = 15
);
   import pkg::*;
    localparam bit2set_flag = bit2test(para2test);   // the code here passed modelsim's compiling
    initial begin
        if (bit2set_flag == 0)
            $error("bit2 of para2test is not set!");
    end
endmodule

can I get it work in interface?