Because Trylon programs are compiled using an intermediate C step, you can use GDB on them. (I recommend CGDB, a nice Curses-based front-end to GDB.) The C code will be a little ugly, but it should be fairly easy to read. (As of this writing, the "-g" flag is automatically passed to the C compiler, so you don't have to add a 'c-flags += "-g"' line to your build-settings.) You'll likely want to put a breakpoint on the SendMessageNotUnderstood_() function in Trylon_.c.

In addition, you should put a "debugging = true" line in your build-settings.local file. This will allow you to use the showObj_() function to inspect objects. For instance:

When stepping into a call, you'll notice that you'll end in the Dispatch_() function. Don't forget about GDB's "f" command, which will get you out of it quickly. In CGDB, you'll quickly become accustomed to the "sfs" idiom.

The compiler will warn you about messages that are sent but never defined. Often this indicates a typo.

There are a couple of types of errors, related to autodeclaration, that are fairly rare, but can be hard to find when they do occur. One is thinking you're auto-declaring a local variable, when you're actually accessing a variable in an outer scope.

(Hopefully it's obvious that "MyPackage" is a directory, and "main" and "MyClass" are files, with their contents shown indented.) In this example, it's likely that the author of "bar:" meant for "name" to be a local variable, but instead "MyPackage name" is being accessed and set. (Older versions of Trylon used "foo := bar" as a syntax for explicitly declaring a local variable. In the early days of the language, it didn't have auto-declaration. The compiler still accepts this, but it's not considered idiomatic Trylon anymore.)

Another, even subtler, error, occurs when you make a typo on the send of a function with one argument. Consider "foo = bar". The compiler turns this into "foo: bar", looks up "foo:", and autodeclares a local named "foo" if "foo:" doesn't exist in the current scope. So suppose you meant to call "print-line:", but instead wrote this:

The compiler wouldn't generate a warning about the use of an undeclared function called "print-lin:". Instead, it's as if you wrote: