The Minimal Asteroid Debugger is a source code debugger for the Asteroid programming language. It supports the following:
- Breakpoints
- Single stepping at the source level
- Stepping through function calls
- Examining contents of variables in the current scope
The commandline interface of the debugger is modeled after debuggers such as the GNU debugger gdb.
In order to invoke the debugger type, :: asteroid -d <FILENAME>
This will start a debugging session of the file <FILENAME>. Here is an example where <FILENAME> is list.ast, :: $ asteroid -d list.ast Minimal Asteroid Debugger -- Version 0.1 (c) University of Rhode Island type 'help' for additional information mad>
During a debugging session the user is able to step through a program and examine its state. The following is debugging session of a program that prints out a sequence of integer values, :: load system io.
- for i in 1 to 5 do
let x = i. io @println x.
end
We start the debugger as shown above. We then set a breakpoint at the first statement in the for loop then continue our computation until it hits the break point. We can then look at the contents of memory. Finally we clear all breakpoints and let the computation finish. Here we go, :: $ asteroid -d list.ast Minimal Asteroid Debugger -- Version 0.1 (c) University of Rhode Island type 'help' for additional information mad> list > 1 load system io. <<<< current line 2 3 for i in 1 to 5 do 4 let x = i. 5 io @println x. mad> set 4 <<<< setting a breakpoint mad> breakpoints breakpoints: list.ast:4 mad> continue <<<< continue execution reached breakpoint (list.ast:4) 1 load system io. 2 3 for i in 1 to 5 do > 4 let x = i. 5 io @println x. 6 end 7 8 [EOF] mad> print i <<<< examining the value of i i: 1 mad> continue 1 reached breakpoint (list.ast:4) 1 load system io. 2 3 for i in 1 to 5 do > 4 let x = i. 5 io @println x. 6 end 7 8 [EOF] mad> print i i: 2 mad> clear <<<< delete breakpoints mad> continue 2 3 4 5 stopping MAD mad> print i i: 5 mad> print x x: 5 mad> quit $
Here is a table of the available commands in the the debugger, :: breakpoints .................... show all breakpoints clear .......................... clear all breakpoints continue ....................... continue execution to next breakpoint down ........................... move down one stack frame frame .......................... display current stack frame number help ........................... display help list ........................... display source code next ........................... step execution across a nested scope print <name><line#> [<file>]] .. set a breakpoint step ........................... step to next executable statement trace .......................... display runtime stack up ............................. move up one stack frame where .......................... print current program line
The or bar | means different options as arguments to the commands. Anything between square brackets is optional. Anything appearing in angle brackets are actual values. For example, print <name> means we want to examine the value of an actual variable, e.g. :: print n
where n is a variable name.
Most commands are very much self-explanatory with the exception of perhaps next. The next command works just like the step command except that it will skip stepping into nested scopes such as function calls or the execution of module statements.