debussy is an excellent waveform viewer. One of the great features of debussy is that you can trace the drivers of signals/registers/etc..
Unfortunately when you are looking at a function and you try to trace the driver of the function return value (which is, admittedly, a somewhat silly thing to do), debussy crashes, which is not so silly.
The function needs to have more than one driver, so you can't do this with a one-line function, but here's a small example:
module top; function joe; begin joe = 1; // Double-click on "joe" in this line joe = 0; end endfunction endmodulefixed in 5.1v2