module fostr

imports
  
  Common

context-free start-symbols
  
  Start

context-free sorts

  Start LineSeq Line OptTermEx TermExLst TermEx Ex

context-free syntax
  
  Start.TopLevel   = LineSeq

  LineSeq          = Line
  LineSeq.Sequence = sq:Line+            {layout(align-list sq)}

  Line             = OptTermEx
  Line.ISequence   = TermExLst OptTermEx {layout(0.first.line == 1.first.line)}

  TermExLst.Prior  = TermEx+

  OptTermEx        = ex:Ex               {layout(offside ex)}
  OptTermEx        = te:TermEx           {layout(offside te)}

  TermEx.Terminate = <<Ex>;>

  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> .> Line+ = Line