(wx:get-single-choice-index message caption choices parent x y center? width height) -> small integer
message : string
caption : string
choices : list of strings
parent = null : wx:window object or null
x = -1 : small integer
y = -1 : small integer
center? = #t : boolean
width = 150 : small integer
height = 200 : small integer
Like
wx:get-single-choice, but the return value is the position of the selected item instead of
the name. If the user presses ``Cancel'', the return value is
-1. The choices are numbered starting from 0.
