module fostr

imports
  
  Common

context-free start-symbols
  
  Start

context-free sorts

  Start LineSeq Line Ex

context-free syntax
  
  Start.TopLevel   = LineSeq

  LineSeq          = <<ln:Ex>> {layout(offside ln)}
  LineSeq.Sequence = sq:Ex+    {layout(align-list sq)}

  Ex+         = Ex+ ln:Ex {layout(offside ln)}

  Ex.Int      = INT
  Ex.Stream   = <stream>
  Ex.Sum      = [[Ex] +  [Ex]] {left}
  Ex.Gets     = [[Ex] << [Ex]] {left}
  Ex.To       = [[Ex] >> [Ex]] {left}

  Ex          = <(<Ex>)> {bracket}

context-free priorities

  Ex.To
  > Ex.Sum
  > Ex.Gets,

  // prevent cycle: no singletons
  LineSeq.Sequence <0> .> Ex+       = Ex,

  // flat: No LineSeq immediately in LineSeq
  Ex+ = Ex <0>     .> LineSeq.Sequence,
  Ex+ = Ex+ Ex <1> .> LineSeq.Sequence