nextSlide :: S.State DocLR0 Slide
nextSlide =
  do doc@DocLR0{slide} <- get
     let newSlide = slide + 1
     put doc{slide = newSlide}
     return newSlide
nextSlide :: S.State DocLR0 Slide
nextSlide =
  do doc@DocLR0{slide} <- get
     let newSlide = slide + 1
     put doc{slide = newSlide}
     return newSlide
nextSlide =
  do doc@DocLR0{slide} <- get
     let newSlide = slide + 1
     put doc{slide = newSlide}
     return newSlide