procedure replace(s1, s2, s3)		#: string replacement
   local result, i

   result := ""
   i := *s2
   if i = 0 then fail			# would loop on empty string

   s1 ? {
      while result ||:= tab(find(s2)) do {
         result ||:= s3
         move(i)
         }
      return result || tab(0)
      }

end