• Maude backend has been discontinued. Please try to convert your definition to the Java backend. If you run into trouble and a particular feature is not supported, please report the feature to us so we can fix it. Limited support for K 3.5 will continue until the release of K 4.0. We will backport bug fixes if necessary. K 4.0 will be released when the Java backend is deemed a suitable complete replacement for maude.
• Removed the K_NAILGUN environment variable: K now uses nailgun whenever it is able to connect to a K server.
• Added an option -w2e to convert all warnings that are not suppressed by the current warning level into errors.
• K_OPTS environment variable now overrides default JVM settings instead of replacing them.
• Many other bugfixes too numerous to list exhaustively. Refer to pull requests on GitHub or contact a K developer for more specific details.

• Users may now use both "requires" and "require", and both "imports" and "import".
• Non-anonymous variables may now contain underscore characters.
• Added an "initial" cell attribute whose effect is to ensure that a multiplicity ? or * cell is part of the initial configuration even if it contains no configuration variables.

• The --directory option now defaults to a value equal to the directory containing the main definition file, rather than the current working directory.

• krun --output raw has been removed. If you are interested in disabling pretty-printing, it is recommended that you try krun --output kast.
• KRun is now much faster. For a complete list of updates, refer to closed pull requests on GitHub.
• Added the --exit-code flag, which specifies a pattern that is matched once rewriting terminates in order to determine a value to return as the exit code of KRun. For more details on how this works, refer to the manual.
• Modified the behavior of --output pretty so that several of the more computation-intensive tasks were not performed. Users interested in the old behavior may now use the new --output sound.

• Added maxValueFloat and minValueFloat functions returning the highest and lowest-magnitude floats for a particular precision and exponent range.
• Added an isInfinite function which returns whether a particular float represents one of the infinities.
• Added a #configuration function which returns the current subject configuration being rewritten.
• Fixed random number generation function.
• Added a 2-argument Float2String method that takes a MPFR printf format string to use to format the floating point number.

• The KRunResult class has been removed. It contained two fields, statistics and rawResult. If you are developing a feature that cannot work effectively without one or both of these fields, please file an issue so that we can evaluate your case and attempt to come up with a new API.
• The kompileOptions() and krunOptions() methods of AbstractKModule now take a class literal instead of an object. The object is constructed from the class by dependency injection (i.e. via a 0-args or @Inject-annotated constructor)
• The LTL model checker interface (currently in use by a third-party plugin) now accepts LTL formulas in the form of a string and is expected to parse them internally using a plugin-specific format.
• External parsers are now expected to output abstract syntax using the new KORE syntax found in k-distribution/include/builtin/kast.k

• Removed --pattern-matching flag and made this behavior the default. Added --symbolic-execution flag, preserving old behavior.
• Added the --audit-step flag. Users may specify a step of execution in the java backend with --audit-step and a rule with --audit-line and --audit-file. The rewriter will then output information indicating whether the rule at that location was executed successfully at that step and if not, why not.
• --statistics on now prints information on the time spent executing the top 10 most expensive-to-compute functions.
• Many improvements made to the K verifier. K verifier is now capable of verifying C programs using the C semantics.

• Discontinued compatibility with Java 7.
• Added an API for users to extend the K framework by means of extending the interface KModule or the abstract class AbstractKModule. Support for:
  • Adding a new backend to Kompile.
  • Adding a new backend to KDoc (see section "Kompile" below).
  • Adding new options to kompile.
  • Adding new options to krun.
  • Adding new hooks to the Java backend.
• Added commands "kserver" and "stop-kserver" to create a local server to run K commands on, implemented using Nailgun. The server is automatically enabled whenever kompile, krun, ktest, kast, or kdoc is run when the K_NAILGUN environment variable is set to a nonempty string. Running applications with nailgun is an experimental feature, subject to certain bugs, but it can be used to increase the speed of executing K programs by a factor of 3-7x.
• Migrated build system from Ant to Maven. For information on building K, refer to the developer README.
• Removed the --backend symbolic option from the distribution. UAIC in Iasi intends to support this functionality using the generic K plugin interface (see "General" above).
• Removed the kagreg tool from the distribution.
• Removed the --debug-gui KRun option from the distribution.

• Changed the KLabel for UserList terminators to '.List{"<KLabel>"} instead of '.List{"<Separator>"}. This allows for a broader range of syntaxes for user lists, as well as the possibility of custom KLabels.
• Changed the syntax of fresh variables from rule foo => N when fresh(N:Int) to rule foo => ?N:Int.
• Added a syntax for fresh constants: rule foo => !N:Int.
• Added a syntax for adding attributes to arbitrary terms: <Term>::Sort{attributes}
• KResult is now a subsort of KItem.

• Changed sorts List, Map, Set to be subsorts of KItem. The tool translates these K expressions into builtin lookups, updates, and selections on the underlying data structures.
• Changed the syntax of set inclusion: SetItem(1) in SetItem(1) no longer returns true. This is to distinguish between a set of elements and a set of sets.
• Removed operations ==Set, ==List, ==Map, =/=Set, =/=List, =/=Map. The correct syntax now is to use ==K for all of these.
• Changed the syntax of Map update from Map [ Value / Key ] to Map [ Key <- Value ].
• Added a new Map difference operator -Map.
• Renamed Map update operator updateMap.
• Separated implementation of Map, List, Set, and MInt sorts from their specification in separate -impl.k files.
• Added syntax predicates isPascalCaseId and isCamelCaseId to refer to Ids which begin with an uppercase or lowercase letter respectively.
• Added a new builtin function #system which operates like the system() syscall.

• Added a type interencer based on context for the sorts of variables.
• Correct the behavior of associativity on productions not of the form syntax Sort ::= Sort1 "op" Sort2
• Added a new syntax for case insensitive terminals: syntax Sort ::= 'terminal'
• Added new attribute "noAutoReject" in order to allow users to provide an infinite set of tokens not to reject.
• Removed the "cons" attribute which was an artifact of the SDF implementation.
• Added the --java-parser and --java-parser-rules options to test the experimental new parser written in Java.
• Added the K function #parseInModule which allows the user to parse input in the syntax of a particular K module.
• Added a friendly error message when the SDF parser crashes.

• Added code which indents Map/List/Set elements from their parent collections.

• Added a new option --legacy-kast which preserves the old behavior of several pieces of functionality which were specific to the Maude implementation.
• kompile --backend [pdf|latex|html|unparse|unflatten|doc] has been moved to a new tool, kdoc --format [pdf|latex|html|unparse|unflatten|doc]
• Modules are required to import or declare constructors for sorts that they use. In the event of a circularity, a forward reference can be introduced using the syntax syntax Sort without any declared productions.
• Added prototype of --backend coq.
• Removed deprecated experimental options --kore, --lib, --loud, --non-symbolic-rules, --symbolic-rules, --rule-index, --test-gen.

• The default output of kast when the --legacy-kast flag is not set on kompile is now the new KORE syntax which will be utilized by K 4.0. This allows users to write external parsers that output this syntax in the Java rewrite engine, a previously unsupported feature. For information about the new syntax, refer to the syntax of KORE. Currently only the KSEQ module is supported by the parser.

• Using JCommander to parse KRun options. See notes for version 3.4 under "Kompile" for details.
• Added option --coverage-file to tell KRun to output rule coverage information.
• Added code to normalize the values of semantic variables in the output of KRun.
• Added support for greater configuration of KRun output modes, including using --output combined with --debugger and others.
• Added new output mode "kast" to represent un-concretized KAST terms.
• Changed syntax for setting a command line parser from --config-var-parser <parser> -cPGM=<term> to -pPGM=<parser> -cPGM=<term>.
• Removed option --backend. Backend is now specified in kompile and read from the compiled definition.
• Removed deprecated options --main-module and --syntax-module. These values are now read from the compiled definition.
• Renamed option --debug-info to --debug for consistency with other tools. Previous --debug for the debugger was renamed to --debugger.
• Changed option --ltlmc to accept only formulas. A file may be specified with the --ltlmc-file option.
• Removed deprecated experimental options --index, --indexing-stats, --generate-tests, --load-cfg.

• Improved the output of KTest to display a message for each running process only when that process is actually run.
• Add a "Running" message to KTest for compilation and pdf generation stages.
• Fixed a minor display issue when using ktest --dry.
• Using JCommander to parse KTest options. See notes for version 3.4 under "Kompile" for details.
• Improved parallelism of KTest by using a common task queue for all processes to be run.
• Changed ordering of KTest execution to execute programs for each definition immediately following compiling that definition.
• ktest --debug now propagates --debug to the kompile, kdoc, and krun processes it generates.

• Significant improvements to the performance and stability of the rewriter.
• Support for rules tagged "anywhere" as long as they rewrite a KItem to a KItem.
• Added support for nested cells of multiplicity * in unification-based rewriter.
• Added support for --superheat and --supercool.
• Added support for rules tagged function which do not have a rewrite at the top.
• Added support for a --trace flag in the matching-based rewriter which prints a list of applied rules.
• Added increased error logging when the rewriter fails with an error.
• --search now respects --transition.

• Updated Z3 API to 4.3.2 beta build bb56885147e4.
• Added substantial additional support for verifying static specifications of programs using the --prove option, which takes a K file containing reachability rules to verify. Features include:
  • SMTLib support for various operations on bit vectors, integers, lists, floats, and booleans.
  • An "smt-lemma" attribute which translates a particular rule into an SMTLib lemma to be used during sat-solving.
  • A "lemma" attribute which treats a rule as a lemma during proving to be additionally verified.
  • Conversion from functions with an "smtlib" attribute to uninterpreted functions in SMTLib.
  • Support for arbitrary bit width of bit vectors variables using "bitwidth" attribute and the new term attribute syntax.
  • Support for arbitrary precision and exponent range of floating point variables using "exponent" and "significand" attributes and the new term attribute syntax.
  • A "pattern" attribute which specifies an associative-commutative-aware configuration abstraction, such as a list or list segment data structure in a heap.
  • A --smt_prelude option to KRun which specifies a prelude to be prepended to SMT queries.
  • A --z3-executable flag to use a separate process for SMT when z3 crashes due to a bug.
  • A "trusted" attribute which specifies that a particular reachability rule should be assumed sound instead of being proven.
  • Options --z3-cnstr-timeout and --z3-impl-timeout to set the Z3 timeout for checking constraints and implications, respectively.
• Removed support for gappa: z3 now handles all the same functionality.

• Added a friendly error message when the tool throws an uncaught exception: Uncaught exception thrown of type ... If you see this error message, please file a bug so that we can either add a better error message, or fix the functionality that caused the error.
  • Also added a flag --debug which provides developers with the original stack trace.
• Changed the name of the K temp directory to .<ToolName>-<Date>-<UUID>.
• Improved error logging in cases where exceptions are caught by K code.
• Converted the K tutorial to use the Java backend for execution instead of Maude.
• Removed a number of unused files from the repository.
• Moved the editor-support folder to the separate repository k-editor-support.

• Fixed Github issues #543, #720, #738, #780, #781, #789, #800, #825, #850, #873, #902, #909, #924, #938, #941, #976, #985, #990, #995, #997, #1047, #1059, #1073, #1088, #1090, #1126, #1153, among many other fixes.

This version is a major release.

• Discontinued compatibility with Java 6.
• New folder structure:
  • Moved editor-support to the top level;
  • Renamed examples to samples
  • Improved and completely reorganized the tutorial
• Removed cink from examples. Cink is a separate repository now.
• The documentation/to-be-processed.txt file contains more information about new features.

• Use of when deprecated; using instead requires (and ensures for proof post-conditions).
• Replaced (deprecated) List{K} by KList (Issue #200).
• Generalized strictness.
• Supporting reject patterns as tags.
• Extending cast functionality with :, ::, <:, :>, <:>.
• Moving the Int, Float, and #String declarations from SDF into K.
• Updated syntax K ::= into syntax KItem ::=.
• Renamed ==MInt and =/=MInt to eqMInt and neMInt.
• Improved the K-defined substitution to deal with arbitrary computations including .K and ~> sequences.

• Added a new plugin for working with K definitions into IntelliJ Idea.

• Using JCommander to handle command line options:
  • breaks code which attempts to access "--" options with only one "-";
  • breaks code which attempts to specify arguments to a parameter with an "=" (except -cFOO=bar)
  • renames experimental options to begin with an X
  • some of the options were renamed. Please check usage.
• kcheck tool was removed
• Added --no-prelude option which skips the auto inclusion of predefined files/modules.
• Implemented support for environment variable K_OPTS to specify additional Java virtual machine arguments (Issue #91).
• Changed kompile to use unique temp files.
• Added a new backend (doc) for documentation generation (experimental).
• Checking tags specified by options like --transition are actually used in rules (Issue #207).
• Improved reporting of running times in the verbose output mode (Issue #169).
• Parsing:
  • block attributes now propagate to individual productions (Issue #186);
  • improved reporting of ambiguities (Issue #182);
  • improved handling of ? variables (Issue #153);
  • improving location information for rules (Issues #73, #108);
  • Anonymous variables are not allowed on the RHS of rewrites;
  • Improved caching of rules to speedup re-compilation if no syntax changes.

• Changed option --output-mode to --output with short-name -o.
• Improved reporting of running times in the verbose output mode (Issue #169).
• --search now accepts more then one token in the input stream (Issue #159).
• Allowing syntactic sorts in --search patterns (Issue #114)
• Search graph is computed by Maude and parsed by krun only if one of the arguments --graph, --debug, or --debug-gui is set (Issue #37).
• Colors: Improved color matching algorithm for terminals. Now more cells should be colored. Added a new krun option: --terminal-color, to specify the background color of the terminal.
• Fixed LTL model checking for negative results (Issue #481).
• Graphical Debugger:
  • save/load configuration;
  • export graph as PNG;
  • improved diff frame;
  • improved duplicate detection for the step-all command.

• Using JCommander to handle kast options
  • breaks code which attempts to access "--" options with only one "-";
  • some of the options were renamed. Please check usage.

• Failing when pdf generation fails (Issue #683).
• Printing tested output file in case of match failure (Issue #689).
• Fixed error messages to contain an executable command (Issue #518).
• Fixed exception reporting (Issues #407, #485).
• Removing redundant messages for skipped steps (Issue #375).
• Fixed color output for non-ANSI terminals (Issue #368).
• Fixed exception thrown by --timeout option (Issue #223).
• Made directory, programs and results arguments absolute paths (Issue #202).
• Show more precise timing information in ktest (Issue #193).
• Generate and update results automatically (Issue #133). New options: --update-out, --generate-out, --dry-run.
• Added --threads parameter.
• Added support for using environment variables in configuration files.
• Changed default value of programs and results options (Issue #99, #93).
• Added --ignore-white-spaces option.
• Support new feature: options more-programs, more-results (Issue #134).
• Multiple program and results directories supported (Issue #96).

• Implementation for builtin string operations.
• Added tag interface for data structure update operations.
• Added option --pattern-matching to krun.
• Adding special autoinclude-java.k for the Java backend.
• Support for maps as cells.
• Added support for proving properties related to floats (using the gappa prover).
• Partial Z3 model integration.

• Option --test-gen added to kompile (experimental)