ALE also provides an XEmacs-based source-level debugger. This can only be used for parsing or definite clause resolution, and only with SICStus 3.7 or higher, and XEmacs 19.15 or higher. In future releases, a debugger with a more restricted functionality will be made available for users of SWI Prolog.
The ALE source-level debugger is implemented on top of the SICStus source-level debugger, and an earlier third-party source-level debugger written by Per Mildner. The debugger provided with ALE has the complete functionality of the SICStus source-level debugger with ordinary Prolog programs; so you only need this one if you will need to debug both. SICStus debugger commands that are not explicitly mentioned in this section are not supported in ALE debugging.
ALE source code must occur in a single file in order to be debugged. To debug Prolog source code, please refer to the SICStus documentation. For both ALE and Prolog debugging, the prolog flag, source_info, needs to be turned on.
When a Prolog hook is encountered while debugging an ALE grammar, the SICStus debugger is automatically invoked. The hook will be embedded in a Prolog call/1 statement. If the leap option of the SICStus debugger is used, the leap ends at the end of the hook -- ALE will creep when it resumes control.
To install the ALE source-level debugger, follow the directions in the distribution file, debugger/INSTALL.