Tue Sep 23 20:20:46 EDT 2014

COS 109 Toy Machine Simulator

(You must have Javascript enabled.) Type your program in the left window. Labels must start in the first column and operators like GET or ADD must start anywhere but the first column, i.e., there must be a space or tab before them. The simulator does not distinguish upper case from lower case, and is generally not robust, so be sure to spell instructions correctly and format code carefully.

Push RUN to run your program. A dialog box will appear when a GET is executed, and output from PRINT will appear in the right window. The simulator will stop if you Cancel a GET or don't enter anything.



Syntax reminder

     get       get a number from keyboard into accumulator
     print     print contents of accumulator
     load Val  load accumulator with Val (Val unchanged)
     store M   store contents of accumulator into memory location called M (accumulator unchanged)
     add Val   add Val to contents of accumulator (Val unchanged)
     sub Val   subtract Val from contents of accumulator (Val unchanged)
     goto L    go to instruction labeled L
     ifpos L   go to instruction labeled L if accumulator is >= zero
     ifzero L  go to instruction labeled L if accumulator is zero
     stop      stop running
   M Num       before program runs, set this memory location (called M) to numeric value Num
If Val is a name like Sum, it refers to a labeled memory location. If Val is a number like 17, that value is used directly. So add Sum means to add the contents of the memory location named Sum to the accumulator value (leaving Sum's contents unchanged), while add 1 means to add 1 to the accumulator value.

If you want to see how the simulator works, Tools / Web Developer / Page Source in Firefox, Customize / Tools / View source in Chrome, or Developer / View Source in Safari.

This version has a limit of 1000 instructions by default, to make it easier to prevent infinite loops. The single-step version has no limit.