Hello! I managed to do it with timeoutAdd: --code below is the onClicked function: drawProgram gui preprocPrg = do let drArea = (drawWin gui) drw <- widgetGetDrawWindow drArea -- let list = compileToList preprocPrg -- renderWithDrawable drw (drawFromList list) renderWithDrawable drw (myDraw 200 200) -- drawWindowProcessUpdates drw True timeoutAdd ((\_ -> do renderWithDrawable drw (myDraw2 200 200) return False) 5) 500 return () But "sometimes" it gives the following error: (<interactive>:23929): Gdk-WARNING **: Using Cairo rendering requires the drawable argument to have a specified colormap. All windows have a colormap, however, pixmaps only have colormap by default if they were created with a non-NULL window argument. Otherwise a colormap must be set on them with gdk_drawable_set_colormap (<interactive>:23929): Gdk-CRITICAL **: IA__gdk_cairo_region: assertion `region != NULL' failed <interactive>: user error (NULL pointer) <interactive>: interrupted <interactive>: warning: too many hs_exit()s What can cause this? I think the other parts of my program are correct, and I cant understand, how can ghci "randomly give" this error. (every 5. try) To be honest, my goal is to make a "turtle graphics" program, so I ll have to write a function, which draws a line on the GUI in slow motion: there will be even more problems with timing, because I ll have to draw the line pixel by pixel.