module desugar
imports libstrategolib signatures/-

rules
  /* ISequence() and Prior() are just noise for more expressions in sequence,
     put in to get the layout rules right. So we remove them and collapse
     all occurrence of them into one big Sequence() call on a list.
     
     This is slightly tricky because there might not be any Sequence() call
     at the top level, but yet an ISequence(). So we do it in two passes,
     first converting ISequence()s to Sequence()s, and then collapsing
     Sequence()s.
  */
  deISe:      ISequence(Prior(l),x) -> Sequence(<conc>(l, [x]))

  seqFlatten: Sequence(l) -> Sequence(<mapconcat(?Sequence(<id>) <+ ![<id>])>l)
  
  defStream:  DefGets(x)  -> Gets(Stream(), x)
  defStream:  DefTo(x)    -> To(x, Stream())
  defStream:  DefEmits()  -> Emits(Stream())

strategies

  desugar-fostr = bottomup(try(defStream <+ deISe <+ seqFlatten))