Prolog Coding Guidelines

General Guidelines

Please ensure that there are no compilation errors or warnings when checking in. Also, try to ensure that there are no errors when loading the files in Spider (Eclipse). Ideally, try to get rid of warnings as well.

Have a look at the paper by [Covington et al.] on Prolog coding guidelines.

Concerning naming of identifiers: try to use names for constants, functors and predicates that are unique and not a prefix of other names. This ensures that one can quickly find all uses/definitions with grep or BBEdit.

Module Information

Every module should be annotated with module information. This is used by our coverage analysis tool.

:- module(MYMODULE, [  exported_predicate/arity, ... ]).

:- use_module(tools).

:- module_info(group,kernel).
:- module_info(description,'This module does wonderful things').

Unit Tests

Unit tests should be setup using the self_check module.

:- use_module(self_check).

Afterwards you can use the following to add new unit tests:

:- assert_must_succeed((bsets_clp:empty_sequence([]))).
:- assert_must_fail((bsets_clp:empty_sequence([int(1)]))).

These tests can be run manually from the ProB Tcl/Tk version, from the command-line using the -self_check command. They will also be automatically run on our jenkins server after committing.


Errors should be raised using one of the add_error predicates in the error_manager module. This will ensure that the errors are brought to the attention of the user in an appropriate way, depending on whether the Rodin, the Tcl/Tk, the command-line version is run and also depending on whether the tool is in testing and/or batch mode.

Note: for internal errors that should never occur use the add_internal_error predicate. This ensures that the coverage information is shown accordingly (in blue rather than red in the highlighting and this also affects coverage statistics).


Preferences should be declared in the preferences module. Each preference must have a default value, a textual description, a type and category. Optionally, a short string for setting the preference from the command-line can be given (using the -p PREF VALUE switch).


  • before committing ensure that probcli can be built (make prob); otherwise git bisect gets annoying to use (one can use git bisect skip to some extent, but it is annoying)
  • run integration tests before pushing your changes (ideally also before committing to avoid later issues with git bisect); ideally you should run as many tests as possible, but at least those affecting the parts you have changed. See alias below to start the test REPL. The command "test" then starts the ProB Test REPL. Type something like "tickets" to run all non-regression tests related to tickets.
  • as a rule of thumb: use rebase before pushing your changes to gitlab, especially when you only have one real commit.
  • avoid merge bombs with many changed files: a Git merge can hide unintended changes, e.g., accidentally reverting previous commits because of editor issues (editor out of sync with file system).
  • provide good commit messages. If a commit is related to a JIRA/Gitlab/Github ticket reference the identifier of the ticket in the commit message. This web page provides the following seven rules:
  • Separate subject from body with a blank line
  • Limit the subject line to 50 characters
  • Capitalize the subject line
  • Do not end the subject line with a period
  • Use the imperative mood in the subject line
  • Wrap the body at 72 characters
  • Use the body to explain what and why vs. how

Useful Bash Aliases

To run probcli from sources:

alias probsli='rlwrap sicstus -l $PROB_SOURCE_DIR/ --goal "go_cli." -a'

To run probcli with the REPL from sources:

alias seval='rlwrap sicstus -l $PROB_SOURCE_DIR/ --goal "go_cli." -a -repl -init -p WARN_WHEN_EXPANDING_INFINITE_CLOSURES 0 -p CLPFD TRUE'

To run ProB Tcl/Tk from sources:

alias prob='unlimit; sics -Dprob_profile=true -l $PROB_SOURCE_DIR/ --goal "go."'

To run the ProB Test REPL from sources:

alias test='cd $PROB_SOURCE_DIR/..; rlwrap sicstus -Dprob_safe_mode=true -l $PROB_SOURCE_DIR/ --goal "test_repl."'