On Fri, 2014-07-11 at 00:50 -0300, Fede wrote about the C64:
machine code monitor
In the beginning I used an assembler, it comes with a similar drawback
as a monitor, but at least there wasn't the need to type the numbers of
the Opcode, it was possible to use the 3 letter abbreviations. Later
there was a macro assembler available, so I used it.