Guard composition

test.shn

function conjoin(a, b)
   meta = { }
   repr = nil
   function meta::__tostring()
      if not repr then
         repr = "%{a} * %{b}"
      end
      return repr
   end

   function meta.__is(v)
      return v is a and v is b
   end
   return meta as meta
end

function disjoin(a, b)
   meta = { }
   repr = nil
   function meta::__tostring()
      if not repr then
         repr = "%{a} + %{b}"
      end
      return repr
   end

   function meta.__is(v)
      return v is a or v is b
   end
end

function ge(n)
   meta = { }
   repr = nil
   function meta::__tostring()
      if not repr then
         repr = "ge %{n}"
      end
      return repr
   end
   function meta::__mul(a, b)
      return conjoin(a, b)
   end
   function meta::__add(a, b)
      return disjoin(a, b)
   end
   function meta.__is(b)
      return b >= n
   end
   return meta as meta
end

function lt(n)
   meta = { }
   repr = nil
   function meta::__tostring()
      if not repr then
         repr = "lt %{n}"
      end
      return repr
   end
   function meta::__mul(a, b)
      return conjoin(a, b)
   end
   function meta::__add(a, b)
      return disjoin(a, b)
   end
   function meta.__is(b)
      return b < n
   end
   return meta as meta
end


x is Number * ge(3) * lt(100) = 5
x = 2