The following implementation is limited to a format string 2x64 = 128 characters long, and six subsequent arguments. %d becomes a decimal number, %e an English one; %c a character, %% a (single) percentage sign and %s a string.

Array printed_text table 64;
Array printf_vals --> 6;
[ Printf format p1 p2 p3 p4 p5 p6   pc j k;
  printf_vals-->0 = p1; printf_vals-->1 = p2; printf_vals-->2 = p3;
  printf_vals-->3 = p4; printf_vals-->4 = p5; printf_vals-->5 = p6;
  printed_text-->0 = 64; @output_stream 3 printed_text;
  print (string) format; @output_stream -3;
  j=printed_text-->0;
  for (k=2:k<j+2:k++)
  {   if (printed_text->k == '%')
      {   switch(printed_text->(++k))
          {   '%': print "%";
              'c': print (char) printf_vals-->pc++;
              'd': print printf_vals-->pc++;
              'e': print (number) printf_vals-->pc++;
              's': print (string) printf_vals-->pc++;
              default: print "<** Unknown printf escape **>";
          }
      }
      else print (char) printed_text->k;
  }
];