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Languages with a slow edit/compile/link/test development loop tend to require sophisticated tracing/stepping debuggers to facilate debugging.
A much better (faster) way in fast-compiling languages is to add printing code at well-selected places, let the program run, look at the output, see where things went wrong, add more printing code, etc., until the bug is found.
The simple debugging aids provided in debugs.fs are meant to support this style of debugging.
The word ~~ prints debugging information (by default the source
location and the stack contents). It is easy to insert. If you use Emacs
it is also easy to remove (C-x ~ in the Emacs Forth mode to
query-replace them with nothing). The deferred words
printdebugdata and .debugline control the output of
~~. The default source location output format works well with
Emacs' compilation mode, so you can step through the program at the
source level using C-x ` (the advantage over a stepping debugger
is that you can step in any direction and you know where the crash has
happened or where the strange data has occurred).
~~ – gforth “tilde-tilde”
Prints the source code location of the ~~ and the stack
contents with .debugline.
printdebugdata – gforth “print-debug-data”
.debugline nfile nline – gforth “print-debug-line”
Print the source code location indicated by nfile nline, and
additional debugging information; the default .debugline
prints the additional information with printdebugdata.
~~ (and assertions) will usually print the wrong file name if a
marker is executed in the same file after their occurance. They will
print `*somewhere*' as file name if a marker is executed in the
same file before their occurance.