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Chapter 5  Reference Manuals for the Why3 Tools

This chapter details the usage of each of the command-line tools provided by the Why3 environment. The main command is why3; it acts as an entry-point to all the features of Why3. It is invoked as such

why3 [general options...] <command> [specific options...]

The following commands are available:

manages the user’s configuration, including the detection of installed provers.
produces HTML versions of Why3 source codes.
performs a symbolic execution of WhyML input files.
generates an OCaml program corresponding to WhyML input files.
provides a graphical interface to display goals and to run provers and transformations on them.
reads WhyML input files and calls provers, on the command-line.
generates interactive proof skeletons for Why3 input files.
replays the proofs stored in a session, for regression test purposes.
dumps various informations from a proof session, and possibly modifies the session.
gives some token statistics about WhyML source files.

All these commands are also available as standalone executable files, if needed.

The commands accept a common subset of command-line options. In particular, option --help displays the usage and options.

-L <dir>
adds <dir> in the load path, to search for theories.
--library <dir>
is the same as -L.
-C <file>
reads the configuration from the given file.
--config <file>
is the same as -C.
--extra-config <file>
reads additional configuration from the given file.
list known debug flags.
list known transformations.
list known printers.
list known provers
list known input formats
list known metas
sets all debug flags (except flags which change the behavior).
--debug <flag>
sets a specific debug flag.
displays the usage and the exact list of options for the given tool.

5.1  The config Command

Why3 must be configured to access external provers. Typically, this is done by running the config command. This must be done each time a new prover is installed.

The provers that Why3 attempts to detect are described in the readable configuration file provers-detection-data.conf of the Why3 data directory (e.g. /usr/local/share/why3). Advanced users may try to modify this file to add support for detection of other provers. (In that case, please consider submitting a new prover configuration on the bug tracking system.)

The result of provers detection is stored in the user’s configuration file (~/.why3.conf or, in the case of local installation, why3.conf in Why3 sources top directory). This file is also human-readable, and advanced users may modify it in order to experiment with different ways of calling provers, e.g. different versions of the same prover, or with different options.

The config command also detects the plugins installed in the Why3 plugins directory (e.g. /usr/local/lib/why3/plugins). A plugin must register itself as a parser, a transformation or a printer, as explained in the corresponding section.

If the user’s configuration file is already present, config will only reset unset variables to default value, but will not try to detect provers. The option --detect-provers should be used to force Why3 to detect again the available provers and to replace them in the configuration file. The option --detect-plugins will do the same for plugins.

If a supported prover is installed under a name that is not automatically recognized by why3config, the option --add-prover will add a specified binary to the configuration. For example, an Alt-Ergo executable /home/me/bin/alt-ergo-trunk can be added as follows:

why3 config --add-prover alt-ergo alt-ergo-trunk /home/me/bin/alt-ergo-trunk

As the first argument, one should put a prover family identification string. The list of known prover families can be obtained by the option --list-prover-families.

5.2  The prove Command

Why3 is primarily used to call provers on goals contained in an input file. By default, such a file must be written in WhyML language (extension .mlw). However, a dynamically loaded plugin can register a parser for some other format of logical problems, e.g. TPTP or SMT-LIB.

The prove command executes the following steps:

  1. Parse the command line and report errors if needed.
  2. Read the configuration file using the priority defined in Section 9.3.
  3. Load the plugins mentioned in the configuration. It will not stop if some plugin fails to load.
  4. Parse and typecheck the given files using the correct parser in order to obtain a set of Why3 theories for each file. It uses the filename extension or the --format option to choose among the available parsers. why3 --list-formats lists the registered parsers. WhyML modules are turned into theories containing verification conditions as goals.
  5. Extract the selected goals inside each of the selected theories into tasks. The goals and theories are selected using options -G/--goal and -T/--theory. Option -T/--theory applies to the previous file appearing on the command line. Option -G/--goal applies to the previous theory appearing on the command line. If no theories are selected in a file, then every theory is considered as selected. If no goals are selected in a theory, then every goal is considered as selected.
  6. Apply the transformations requested with -a/--apply-transform in their order of appearance on the command line. why3 --list-transforms lists the known transformations; plugins can add more of them.
  7. Apply the driver selected with the -D/--driver option, or the driver of the prover selected with the -P/--prover option. why3 --list-provers lists the known provers, i.e. the ones that appear in the configuration file.
  8. If option -P/--prover is given, call the selected prover on each generated task and print the results. If option -D/--driver is given, print each generated task using the format specified in the selected driver.

5.2.1  Prover Results

The provers can give the following output:

The goal is proved in the given context.
The prover has stopped its search.
The prover has reached the time limit.
An error has occurred.
The prover knows the goal cannot be proved.

5.2.2  Additional Options

--extra-expl-prefix <s>
specifies s as an additional prefix for labels that denotes VC explanations. The option can be used several times to specify several prefixes.

5.2.3  Getting Potential Counterexamples

That feature is presented in details in Section 5.3.7, that should be read first.

Counterexamples are also displayed by the why3 prove command when one selects a prover with the counterexamples alternative. The output is currently done in a JSON syntax (this may change in the future).

5.3  The ide Command

The basic usage of the GUI is described by the tutorial of Section 1.2. The command-line options are the common options detailed in introduction to this chapter, plus the specific option already described for the command prove in Section 5.2.2.

--extra-expl-prefix <s>

At least one anonymous argument must be specified on the command line. More precisely, the first anonymous argument must be the directory of the session. If the directory does not exist, it is created. The other arguments should be existing files that are going to be added to the session. For convenience, if there is only one anonymous argument, it can be an existing file and in this case the session directory is obtained by removing the extension from the file name.

We describe the actions of the various menus and buttons of the interface.

5.3.1  Session

Why3 stores in a session the way you achieve to prove goals that come from a file (.why), from weakest-precondition (.mlw) or by other means. A session stores which file you prove, by applying which transformations, by using which prover. A proof attempt records the complete name of a prover (name, version, optional attribute), the time limit and memory limit given, and the result of the prover. The result of the prover is the same as when you run the prove command. It contains the time taken and the state of the proof:

The task is valid according to the prover. The goal is considered proved.
The task is invalid.
the prover exceeded the time limit.
The prover exceeded the memory limit.
The prover cannot determine if the task is valid. Some additional information can be provided.
The prover reported a failure.
An error occurred while trying to call the prover, or the prover answer was not understood.

Additionally, a proof attempt can have the following attributes:

The prover associated to that proof attempt has not been run on the current task, but on an earlier version of that task. You need to replay the proof attempt, i.e. run the prover with the current task of the proof attempt, in order to update the answer of the prover and remove this attribute.
The proof attempt is not associated to a proof task anymore. The reason might be that a proof goal disappeared, or that there is a syntax or typing error in the current file, that makes all nodes temporarily detached until the parsing error is fixed. Detached nodes of the session tree are kept until they are explicitly removed, either using a remove command or the clean command. They can be reused, as any other nodes, using the copy/paste operation.

Generally, proof attempts are marked obsolete just after the start of the user interface. Indeed, when you load a session in order to modify it (not with why3session info for instance), Why3 rebuilds the goals to prove by using the information provided in the session. If you modify the original file (.mlw) or if the transformations have changed (new version of Why3), Why3 will detect that. Since the provers might answer differently on these new proof obligations, the corresponding proof attempts are marked obsolete.

5.3.2  Context Menu

The left toolbar that was present in former versions of Why3 is now replaced by a context menu activited by clicking the right mouse button, while cursor is on a given row of the proof session tree.

The detected provers are listed. Note that you can hide some provers of that list using the preferences, tab Provers.
the set of known strategies is listed
starts an editor on the selected task.
Replay valid obsolete proofs
all proof nodes below the selected nodes that are obsolete but whose former status was Valid are replayed.
Replay all obsolete proofs
all proof nodes below the selected nodes that are obsolete are replayed.
removes a proof attempt or a transformation.
removes any unsuccessful proof attempt for which there is another successful proof attempt for the same goal
cancels all the proof attempts currently scheduled or running.

5.3.3  Global Menus

Menu File
Add File to session
adds a file in the current proof session.
opens a window for modifying preferred configuration parameters, see details below.
Save session
saves current session state on disk. The policy to decide when to save the session is configurable, as described in the preferences below.
Save files
saves edited soruce files on disk.
Save session and files
saves both current session state and edited files on disk.
Save all and Refresh session
save session and edited files, and refresh the current session tree.
exits the GUI.
Menu Tools
section provides a set of actions that are performed on the selected goal(s):
Split VC
splits the current goal into subgoals.
Auto level 0
is a basic proof search strategy that applies a few provers on the goal with a short time limit.
Auto level 1
is a strategy that first applies a few provers on the goal with a short time limit, then splits the goal and tries again on the subgoals
Auto level 2
is a strategy more elaborate than level 1, that attempts to apply a few transformations that are typically useful. It also tries the provers with a larger time limit.
A more detailed description of strategies is given in Section 9.6, as well as a description on how to design strategies of your own.
provide a menu item for each detected prover. Clicking on such an item starts the corresponding prover on the selected goal(s). To start a prover with a different time limit, you may either change the default time limit in the Preferences, or using the text command field and type the prover name followed by the time limit.
gives access to all the known transformations.
starts an editor on the selected task.

For automatic provers, this allows to see the file sent to the prover.

For interactive provers, this also allows to add or modify the corresponding proof script. The modifications are saved, and can be retrieved later even if the goal was modified.

Replay valid obsolete proofs
replays all the obsolete proofs below the current node whose former state was Valid.
Replay all obsolete proofs
replays all the obsolete proofs below the current node.
removes any unsuccessful proof attempt for which there is another successful proof attempt for the same goal
removes a proof attempt or a transformation.
Mark obsolete
marks all the proof as obsolete. This allows to replay every proof.
cancels all the proof attempts currently scheduled or running.
performs a reduction of the context for the the current selected proof attempt, which must be a Valid one.
focus the tree session view to the current node
undoes the Focus action
Marks of proof sub-tree for copy/past action
Paste the previously selected sub-tree under the current node
Menu View
Enlarge font
selects a large font
Reduce font
selects a smaller font
Collapse proved goals
closes all the rows of the tree view that are proved.
Expand All
expands all the rows of the tree view.
Collapse under node
closes all the rows of the tree view under the given node that are proved.
Expand below node
expands the children below the current node
Expand all below node
expands the whole subtree of the current node
Go to parent node
move to the parent of the current node
Go to first child
mode to the first child of the current node
Select next unproven goal
go to the next unproven goal after the current node
Menu Help
Explanations of the meaning of the various icons
some information about this software.

5.3.4  Command-line interface

Between the top-right zone containing source files and task, and the bottom-right zone containing various messages, a text input field allows the user to invoke commands using a textual interface (see Figure 1.1). The ’help’ command displays a basic list of available commands. All commands available in the menus are also available as a textual command. However the textual interface allows for much more possibilities, including the ability to invoke transformations with arguments.

5.3.5  Key shortcuts

5.3.6  Preferences Dialog

The preferences dialog allows you to customize various settings. They are grouped together under several tabs.

Note that there are to different buttons to close that dialog. The “Close” button will make modifications of any of these settings effective only for the current run of the GUI. The “Save&Close” button will save the modified settings in Why3 configuration file, to make them permanent.

General Settings tab
allows one to set various general settings.
Appearance settings tab
  Finally, it is possible to choose an alternative icon set, provided, one is installed first.
Editors tab
allows one to customize the use of external editors for proof scripts.
Provers tab
allows to select which of the installed provers one wants to see in the context menu.
Uninstalled Provers tab
presents all the decision previously taken for missing provers, as described in Section 4.2.2. You can remove any recorded decision by clicking on it.

5.3.7  Displaying Counterexamples

Why3 provides some support for extracting a potential counterexample from failing proof attempts, for provers that are able to produce a counter-model of the proof task. Why3 attempts to turn this counter-model into values for the free variables of the original Why3 input. Currently, this is supported for CVC4 prover version at least 1.5, and Z3 prover version at least 4.4.0.

The generation of counterexamples is fully integrated in Why3 IDE. The recommended usage is to first start a prover normally, as shown in Figure 5.1) and then click on the status icon for the corresponding proof attempt in the tree. Alternatively, one can use the key shortcut “G” or type get-ce in the command entry. The result can be seen on Figure 5.2: the same prover but with the alternative counterexamples is run. The resulting counterexample is displayed in two different ways. First, it is displayed in the Task tab of the top-right window, at the end of the text of the task, under the form of a list of pairs “variable = value”, ordered by the line number of the source code in which that variable takes that value. Second, it is displayed in the Counterexample tab of the bottom right window, this time interleaved with the code, as shown in Figure 5.2.

Figure 5.1: Failing execution of CVC4

Figure 5.2: Counterexamples display for CVC4

Notes on format of displayed values

The counterexamples can contain values of various types.

To detail the display of map values, consider the following code with a trivially false postcondition:

use int.Int use ref.Ref use map.Map let ghost test_map (ghost x : ref (map int int)) : unit ensures { !x[0] <> !x[1] } = x := Map.set !x 0 3

Executing CVC4 with the “counterexamples” alternative on goal will trigger counterexamples:

use int.Int use ref.Ref use map.Map let ghost test_map (ghost x : ref (map int int)) : unit (* x = (1 => 3,others => 0) *) ensures { !x[0] <> !x[1] } (* x = (0 => 3,1 => 3,others => 0) *) = x := Map.set !x 0 3 (* x = (0 => 3,1 => 3,others => 0) *)

The notation for map is to be understood with indices on left of the arrows and values on the right “(index => value)”. The meaning of the keyword others is the value for all indices that were not mentioned yet. This shows that setting the parameter x to a map that has value 3 for index 1 and zero for all other indices is a counterexample. We can check that this negates the Why3ensures clause.

Known limitations

The counterexamples are known not to work on the following non-exhaustive list (which is undergoing active development):

More information on the implementation of counterexamples in Why3 can be found in [7] and in [5]. For the producing counterexamples using the Why3 API, see Section 3.10.

5.4  The replay Command

The replay command is meant to execute the proofs stored in a Why3 session file, as produced by the IDE. Its main purpose is to play non-regression tests. For instance, examples/ is a script that runs regression tests on all the examples.

The tool is invoked in a terminal or a script using

why3 replay [options] <project directory>

The session file why3session.xml stored in the given directory is loaded and all the proofs it contains are rerun. Then, all the differences between the information stored in the session file and the new run are shown.

Nothing is shown when there is no change in the results, whether the considered goal is proved or not. When all the proof are done, a summary of what is proved or not is displayed using a tree-shape pretty print, similar to the IDE tree view after doing “Collapse proved goals”. In other words, when a goal, a theory, or a file is fully proved, the subtree is not shown.

Obsolete proofs

When some proof attempts stored in the session file are obsolete, the replay is run anyway, as with the replay button in the IDE. Then, the session file will be updated if both

In other cases, you can use the IDE to update the session, or use the option --force described below.

Exit code and options

The exit code is 0 if no difference was detected, 1 if there was. Other exit codes mean some failure in running the replay.

Options are:

suppresses the output of the final tree view.
runs quietly (no progress info).
enforces saving the session, if all proof attempts replayed correctly, even if some goals are not proved.
replays the proofs only if the session contains obsolete proof attempts.
--smoke-detector {none|top|deep}
tries to detect if the context is self-contradicting.
--prover <prover>
restricts the replay to the selected provers only.
Smoke detector

The smoke detector tries to detect if the context is self-contradicting and, thus, that anything can be proved in this context. The smoke detector can’t be run on an outdated session and does not modify the session. It has three possible configurations:

Do not run the smoke detector.
The negation of each proved goal is sent with the same timeout to the prover that proved the original goal.
  Goal G : forall x:int. q x -> (p1 x \/ p2 x)
  Goal G : ~ (forall x:int. q x -> (p1 x \/ p2 x))
In other words, if the smoke detector is triggered, it means that the context of the goal G is self-contradicting.
This is the same technique as top but the negation is pushed under the universal quantification (without changing them) and under the implication. The previous example becomes
  Goal G : forall x:int. q x /\ ~ (p1 x \/ p2 x)
In other words, the premises of goal G are pushed in the context, so that if the smoke detector is triggered, it means that the context of the goal G and its premises are self-contradicting. It should be clear that detecting smoke in that case does not necessarily means that there is a mistake: for example, this could occur in the WP of a program with an unfeasible path.

At the end of the replay, the name of the goals that triggered the smoke detector are printed:

  goal 'G', prover 'Alt-Ergo 0.93.1': Smoke detected!!!

Moreover Smoke detected (exit code 1) is printed at the end if the smoke detector has been triggered, or No smoke detected (exit code 0) otherwise.

5.5  The session Command

The session command makes it possible to extract information from proof sessions on the command line, or even modify them to some extent. The invocation of this program is done under the form

why3 session <subcommand> [options] <session directories>

The available subcommands are as follows:

prints informations and statistics about sessions.
outputs session contents in LaTeX format.
outputs session contents in HTML format.
update session contents.

The first three commands do not modify the sessions, whereas the last modify them.

5.5.1  Command info

The command why3 session info reports various informations about the session, depending on the following specific options.

prints the provers that appear inside the session, one by line.
prints all the files that appear in the session as edited proofs.
prints various proofs statistics, as detailed below.
separates the results of the options provers and --edited-files by the character number 0 instead of end of line \n. That allows you to safely use (even if the filename contains space or carriage return) the result with other commands. For example you can count the number of proof line in all the coq edited files in a session with:
why3 session info --edited-files vstte12_bfs --print0 | xargs -0 coqwc
or you can add all the edited files in your favorite repository with:
why3 session info --edited-files --print0 vstte12_bfs.mlw | \
    xargs -0 git add
Session Statistics

The proof statistics given by option --stats are as follows:

For example, here are the session statistics produced on the “hello proof” example of Section 1.

== Number of root goals ==
  total: 3  proved: 2

== Number of sub goals ==
  total: 2  proved: 1

== Goals not proved ==
  +-- file ../hello_proof.why
    +-- theory HelloProof
      +-- goal G2
        +-- transformation split_goal_right
          +-- goal G2.0

== Goals proved by only one prover ==
  +-- file ../hello_proof.why
    +-- theory HelloProof
      +-- goal G1: Alt-Ergo 0.99.1
      +-- goal G2
        +-- transformation split_goal_right
          +-- goal G2.1: Alt-Ergo 0.99.1
      +-- goal G3: Alt-Ergo 0.99.1

== Statistics per prover: number of proofs, time (minimum/maximum/average) in seconds ==
  Alt-Ergo 0.99.1     :   3   0.00   0.00   0.00

5.5.2  Command latex

Command latex produces a summary of the replay under the form of a tabular environment in LaTeX, one tabular for each theory, one per file.

The specific options are

-style <n>
sets output style (1 or 2, default 1) Option -style 2 produces an alternate version of LaTeX output, with a different layout of the tables.
-o <dir>
indicates where to produce LaTeX files (default: the session directory).
uses the ‘longtable’ environment instead of ‘tabular’.
-e <elem>
produces a table for the given element, which is either a file, a theory or a root goal. The element must be specified using its path in dot notation, e.g. file.theory.goal. The file produced is named accordingly, e.g. file.theory.goal.tex. This option can be given several times to produce several tables in one run. When this option is given at least once, the default behavior that is to produce one table per theory is disabled.
Customizing LaTeX output

The generated LaTeX files contain some macros that must be defined externally. Various definitions can be given to them to customize the output.

macro with one parameter, a prover name
macro with one parameter, used where the corresponding prover answers that the goal is valid. The parameter is the time in seconds.
macro without parameter, used where no result exists for the corresponding prover
macro without parameter, used where the corresponding prover reached the time limit
macro with one parameter, the goal name or its explanation

\usepackage{xcolor} \usepackage{colortbl} \usepackage{rotating} \newcommand{\provername}[1]{\cellcolor{yellow!25} \begin{sideways}\textbf{#1}~~\end{sideways}} \newcommand{\explanation}[1]{\cellcolor{yellow!13}lemma \texttt{#1}} \newcommand{\transformation}[1]{\cellcolor{yellow!13}transformation \texttt{#1}} \newcommand{\subgoal}[2]{\cellcolor{yellow!13}subgoal #2} \newcommand{\valid}[1]{\cellcolor{green!13}#1} \newcommand{\unknown}[1]{\cellcolor{red!20}#1} \newcommand{\invalid}[1]{\cellcolor{red!50}#1} \newcommand{\timeout}[1]{\cellcolor{red!20}(#1)} \newcommand{\outofmemory}[1]{\cellcolor{red!20}(#1)} \newcommand{\noresult}{\multicolumn{1}{>{\columncolor[gray]{0.8}}c|}{~}} \newcommand{\failure}{\cellcolor{red!20}failure} \newcommand{\highfailure}{\cellcolor{red!50}FAILURE}
Figure 5.3: Sample macros for the LaTeX command

Figure 5.4: LaTeX table produced for the HelloProof example (style 1)

Figure 5.5: LaTeX table produced for the HelloProof example (style 2)

Figure 5.3 suggests some definitions for these macros, while Figures 5.4 and 5.5 show the tables obtained from the HelloProof example of Section 1, respectively with style 1 and 2.

5.5.3  Command html

This command produces a summary of the proof session in HTML syntax. There are two styles of output: ‘table’ and ‘simpletree’. The default is ‘table’.

The file generated is named why3session.html and is written in the session directory by default (see option -o to override this default).

Why3 Proof Results for Project "hello_proof"

Theory "hello_proof.HelloProof": not fully verified

ObligationsAlt-Ergo 0.99.1Coq 8.7.1
Figure 5.6: HTML table produced for the HelloProof example

The style ‘table’ outputs the contents of the session as a table, similar to the LaTeX output above. Figure 5.6 is the HTML table produced for the ‘HelloProof’ example, as typically shown in a Web browser. The gray cells filled with --- just mean that the prover was not run on the corresponding goal. Green background means the result was “Valid”, other cases are in orange background. The red background for a goal means that the goal was not proved.

The style ‘simpletree’ displays the contents of the session under the form of tree, similar to the tree view in the IDE. It uses only basic HTML tags such as <ul> and <li>.

Specific options for this command are as follows.

--style <style>
sets the style to use, among simpletree and table; defaults to table.
-o <dir>
sets the directory where to output the produced files (‘-’ for stdout). The default is to output in the same directory as the session itself.
adds context around the generated code in order to allow direct visualization (header, css, ...). It also adds in the output directory all the needed external files. It can’t be set with stdout output.
--add_pp <suffix> <cmd> <out_suffix>
sets a specific pretty-printer for files with the given suffix. Produced files use <out_suffix> as suffix. <cmd> must contain ‘%i’ which will be replaced by the input file and ‘%o’ which will be replaced by the output file.
uses the coqdoc command to display Coq proof scripts. This is equivalent to --add_pp .v "coqdoc --no-index --html -o %o %i" .html

5.5.4  Command update

The command why3 session update permits to modify the session contents, depending on the following specific options.

-rename-file <src> <dst>
renames the file <src> to <dst> in the session. The file <src> itself is also renamed to <dst> in your filesystem.

5.6  The doc Command

This tool can produce HTML pages from Why3 source code. Why3 code for theories or modules is output in preformatted HTML code. Comments are interpreted in three different ways.

Additionally, all the Why3 identifiers are typeset with links so that one can navigate through the HTML documentation, going from some identifier use to its definition.

-o <dir>
defines the directory where to output the HTML files.
--output <dir>
is the same as -o.
generates an index file index.html. This is the default behavior if more than one file is passed on the command line.
prevents the generation of an index file.
--title <title>
sets title of the index page.
--stdlib-url <url>
sets a URL for files found in load path, so that links to definitions can be added.
Typesetting textual comments

Some constructs are interpreted:

A CSS file style.css suitable for rendering is generated in the same directory as output files. This CSS style can be modified manually, since regenerating the HTML documentation will not overwrite an existing style.css file.

5.7  The execute Command

Why3 can symbolically execute programs written using the WhyML language (extension .mlw). See also Section 7.1.

5.8  The extract Command

Why3 can extract programs written using the WhyML language (extension .mlw) to OCaml. See also Section 7.2.

5.9  The realize Command

Why3 can produce skeleton files for proof assistants that, once filled, realize the given theories. See also Section 8.2.

5.10  The wc Command

Why3 can give some token statistics about WhyML source files.

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