Coding in the Debugger (2007)

Here's an anecdote I heard once about Minsky. He was showing a student how to use ITS to write a program. ITS was an unusual operating system in that the 'shell' was the DDT debugger. You ran programs by loading them into memory and jumping to the entry point. But you can also just start writing assembly code directly into memory from the DDT prompt. Minsky started with the null program. Obviously, it needs an entry point, so he defined a label for that. He then told the debugger to jump to that label. This immediately raised an error of there being no code at the jump target. So he wrote a few lines of code and restarted the jump instruction. This time it succeeded and the first few instructions were executed. When the debugger again halted, he looked at the register contents and wrote a few more lines. Again proceeding from where he left off he watched the program run the few more instructions. He developed the entire program by 'debugging' the null program.