[Inkscape-devel] function plotter broken

Help requested from Python extension developers -

in SVN, the function plotter dialog is broken:

File "/usr/local/share/inkscape/extensions/funcplot.py", line 115, in drawfunction dy0 = (y1 - y0)/ds TypeError: unsupported operand type(s) for -: 'str' and 'str'

I have no idea what is wrong and why it worked before.