gtk:text-buffer-place-cursor (buffer pos)

buffer -- a gtk:text-buffer object
pos -- a gtk:text-iter iterator where to put the cursor

This function moves the "insert" and "selection_bound" marks simultaneously. If you move them to the same place in two steps with the gtk:text-buffer-move-mark function, you will temporarily select a region in between their old and new locations, which can be pretty inefficient since the temporarily selected region will force stuff to be recalculated. This function moves them as a unit, which can be optimized.