text: create lua set script
  SET_RETURNS(x double, y double)
  returns double as
  function run(ctx)
  local acc = 0.0
  repeat
  acc = acc + ctx.x + ctx.y
  until not ctx.next()
          return acc
  end
  /
  
  
  
  create lua set script
  SET_EMITS(x double, y double)
  emits (x double, y double) as
  function run(ctx)
  repeat
                  ctx.emit(ctx.y, ctx.x)
                  until not ctx.next()
  end
  /
  
  
  
  create lua scalar script
  SCALAR_RETURNS(x double, y double)
  returns double as
  function run(ctx)
       return ctx.x + ctx.y
  end
  /
  
  
  create lua scalar script
  SCALAR_EMITS(x double, y double)
  emits (x double, y double) as
  function run(ctx)
           for i = ctx.x, ctx.y do
               ctx.emit(i, i * i)
           end
  end
  /
  