NEWS

This file contains a summary of important user-visible changes.

Changes since 1.7
=================

New Features:
* New C++ and Python API: CVC4 has a new, more streamlined API. We plan to
  make CVC4 1.8 the last version that ships with the legacy API.
* Strings: Full support of the new SMT-LIB standard for the theory of strings,
  including:
  * Support for `str.replace_re`, `str.replace_re_all`, `str.is_digit`,
    `str.from_code`, `re.diff`, and `re.comp`
  * Support for new operator names (e.g. `str.in_re` instead of `str.in.re`),
    new escape sequences. The new syntax is enabled by default for smt2 files.
* Support for syntax-guided synthesis (SyGuS) problems in the new API. C++
  examples of the SyGuS API can be found in `./examples/api/sygus_*.cpp`.
* Support for higher-order constraints. This includes treating function sorts
  (constructible by `->`) as first-class sorts and handling partially applied
  function symbols. Support for higher-order constraints can be enabled by
  the option `--uf-ho`.
* Support for set comprehension binders `comprehension`.
* Eager bit-blasting: Support for SAT solver Kissat.

Improvements:
* API: Function definitions can now be requested to be global. If the `global`
  parameter is set to true, they persist after popping the user context.
* Java/Python bindings: The bindings now allow users to catch exceptions
* Arithmetic: Performance improvements
  * Linear solver: New lemmas inspired by unit-cube tests
  * Non-linear solver: Expanded set of axioms
* Ackermannization: The Ackermannization preprocessing pass now supports
  uninterpreted sorts and as a result all QF_UFBV problems are supported in
  combination with eager bit blasting.

Changes:
* CVC language: Models printed in the CVC language now include an explicit end
  marker to facilitate the communication over pipes with CVC4.
* API change: `SmtEngine::query()` has been renamed to
  `SmtEngine::checkEntailed()` and `Result::Validity` has been renamed to
  `Result::Entailment` along with corresponding changes to the enum values.
* Java API change: The name of CVC4's package is now `edu.stanford.CVC4`
  instead of `edu.nyu.acsys.CVC4`.
* The default output language is changed from CVC to SMT-LIB 2.6. The
  default output language is used when the problem language cannot be
  easily inferred (for example when CVC4 is used from the API).
* Printing of BV constants: previously CVC4 would print BV constant
  values as indexed symbols by default and in binary notation with the
  option --bv-print-consts-in-binary. To be SMT-LIB compliant the
  default behavior is now to print BV constant values in binary
  notation and as indexed symbols with the new option
  --bv-print-consts-as-indexed-symbols. The option
  --bv-print-consts-in-binary has been removed.
* Updated to SyGuS language version 2.0 by default. This is the last release
  that will support the SyGuS language version 1.0 (`--lang=sygus1`). A
  script is provided to convert version 1.0 files to version 2.0, see
  `./contrib/sygus-v1-to-v2.sh`.
* Support for user-provided rewrite rule quantifiers have been removed.
* Support for certain option aliases have been removed.
* Support for parallel portfolio builds has been removed.

Changes since 1.6
=================

New Features:
* Proofs:
  * Support for bit-vector proofs with eager bitblasting (older versions only
    supported proofs with lazy bitblasting).
* Strings:
  * Support for `str.replaceall` operator.
  * New option `--re-elim` to reduce regular expressions to extended string
    operators, resulting in better performance on regular expression benchmarks
    (enabled by default).
* SyGuS:
  * Support for abduction (`--sygus-abduct`). Given a formula, this option uses
    CVC4's SyGuS solver to find a sufficient condition such that the
    conjunction of the condition and the formula is unsatisfiable.
  * Support for two new term enumerator strategies: variable agnostic
    (`--sygus-active-gen=var-agnostic`) and fast (`--sygus-active-gen=enum`).
    By default, CVC4 tries to choose the best term enumerator strategy
    automatically based on the input (`--sygus-active-gen=auto`).
  * Support for streaming solutions of increasingly smaller size when using the
    PBE solver (`--sygus-stream --sygus-pbe`). After the first solution is found
    and printed, the solver will continue to look for new solutions and print
    those, if any, that are smaller than previously printed solutions.
  * Support for unification-based techniques in non-separable specifications
    (`--sygus-unif`). For solving invariant problems a dedicate mode
    (`--sygus-unif-boolean-heuristic-dt`) is available that builds candidate
    solutions using heuristic decision tree learning.

Improvements:
* Strings:
  * Significantly better performance on string benchmarks over the core theory
    and those with extended string functions like substring, contains, and
    replace.

Changes:
* API change: Expr::iffExpr() is renamed to Expr::eqExpr() to reflect its
              actual behavior.
* Compiling the language bindings now requires SWIG 3 instead of SWIG 2.
* The CVC3 compatibility layer has been removed.
* The build system now uses CMake instead of Autotools. Please refer to
  [INSTALL.md](https://github.com/CVC4/CVC4/blob/master/INSTALL.md) for
  up-to-date instructions on how to build CVC4.

Changes since 1.5
=================

New Features:
* A new theory of floating points.
* Novel approach for solving quantified bit-vectors (BV).
* Eager bit-blasting: Support for SAT solver CaDiCaL.
* A new Gaussian Elimination preprocessing pass for the theory of bit-vectors.
* Support for transcendental functions (sin, cos, exp). In SMT2 input, this
  can be enabled by adding T to the logic (e.g., QF_NRAT).
* Support for new operators in strings, including string inequality (str.<=)
  and string code (str.code).
* Support for automated rewrite rule generation from sygus (*.sy) inputs using
  syntax-guided enumeration (option --sygus-rr).

Improvements:
* Incremental unsat core support.
* Further development of rewrite rules for the theory of strings and regular
  expressions.
* Many optimizations for syntax-guided synthesis, including improved symmetry
  breaking for enumerative search and specialized algorithms for
  programming-by-examples conjectures.

Changes:
* Eager bit-blasting: Removed support for SAT solver CryptoMinisat 4, added
  support for CryptoMinisat 5.
* The LFSC proof checker now resides in its own repository on GitHub at
  https://github.com/CVC4/LFSC. It is not distributed with CVC4 anymore.

Changes since 1.4
=================

* Improved heuristics for reasoning about non-linear arithmetic.
* Native support for syntax-guided synthesis (sygus).
* Support for many new heuristics for reasoning with quantifiers, including
  finite model finding.
* Support for proofs for uninterpreted functions, arrays, bitvectors, and
  their combinations.
* Performance improvements to existing theories.
* A new theory of sets with cardinality and relations.
* A new theory of strings.
* Support for unsat cores.
* Support for separation logic constraints.
* Simplification mode "incremental" no longer supported.
* Support for array constants in constraints.
* Syntax for array models has changed in some language front-ends.
* New input/output languages supported: "smt2.0" and "smtlib2.0" to
  force SMT-LIB v2.0; "smt2.5" and "smtlib2.5" to force SMT-LIB v2.5;
  "smt2.6" and "smtlib2.6" to force SMT-LIB v2.6;
  "smt", "smtlib", "smt2", and "smtlib2" all refer to the current standard
  version 2.6.  If an :smt-lib-version is set in the input, that overrides
  the command line.
* Abstract values in SMT-LIB models are now ascribed types (with "as").
* In SMT-LIB model output, real-sorted but integer-valued constants are
  now printed in accordance with the standard (e.g. "1.0").

Changes since 1.3
=================

* CVC4 now supports libc++ in addition to libstdc++ (this especially
  helps on Mac OS Mavericks).
* The LFSC proof checker has been incorporated into CVC4 sources.
* Theory of finite sets, handling the MLSS fragment (singleton, union,
  intersection, set subtraction, membership and subset).
* By default, CVC4 builds in "production" mode (optimized, with fewer
  internal checks on).  The common alternative is a "debug" build, which
  is much slower.  By default, CVC4 builds with no GPL'ed dependences.
  However, this is not the best-performing version; for that, you should
  configure with "--enable-gpl --best", which links against GPL'ed
  libraries that improve usability and performance.  For details on
  licensing and dependences, see the README file.
* Small API adjustments to Datatypes to even out the API and make it
  function better in Java.
* Timed statistics are now properly updated even on process abort.
* Better automatic handling of output language setting when using CVC4
  via API.  Previously, the "automatic" language setting was sometimes
  (though not always) defaulting to the internal "AST" language; it
  should now (correctly) default to the same as the input language
  (if the input language is supported as an output language), or the
  "CVC4" native output language if no input language setting is applied.
* The SmtEngine cannot be safely copied with the copy constructor.
  Previous versions inadvertently permitted clients to do this via the
  API.  This has been corrected, copy and assignment of the SmtEngine
  is no longer permitted.

Changes since 1.2
=================

New features:
* SMT-LIB-compliant support for abs, to_real, to_int, is_int, which were
  previously missing
* New bv2nat/int2bv operators for bitvector/integer inter-compatibility.
* Support in linear logics for /, div, and mod by constants (with the
  --rewrite-divk command line option).
* Parsing support for TPTP's TFF and TFA formats.
* A new theory of strings: word (dis-)equations, length constraints,
  regular expressions.
* Increased compliance to SMT-LIBv2, numerous bugs and usability issues
  resolved.
* New :command-verbosity SMT option to silence success and error messages
  on a per-command basis, and API changes to Command infrastructure to
  support this.

Behavioral changes:
* It is no longer permitted to request model or proof generation if there's
  been an intervening push/pop.
* User-defined symbols (define-funs) are no longer reported in the output
  of get-model commands.
* Exit codes are now more standard for UNIX command-line tools.  Exit code
  zero means no error---but the result could be sat, unsat, or unknown---and
  nonzero means error.

API changes:
* Expr::substitute() now capable of substituting operators (e.g.,
  function symbols under an APPLY_UF)
* Numerous improvements to the Java language bindings

Changes since 1.1
=================

* Real arithmetic now has three simplex solvers for exact precision linear
  arithmetic: the classical dual solver and two new solvers based on
  techniques for minimizing the sum of infeasibilities. GLPK can now be used
  as a heuristic backup to the exact precision solvers.  GLPK must be enabled
  at configure time. See --help for more information on enabling these solvers.
* added support for "bit0" and "bit1" bitvector constants in SMT-LIB v1.2
* support for theory "alternates": new ability to prototype new decision
  procedures that are selectable at runtime
* various bugfixes

Changes since 1.0
=================

* bit-vector solver now has a specialized decision procedure for unsigned bit-
  vector inequalities
* numerous important bug fixes, performance improvements, and usability
  improvements
* support for multiline input in interactive mode
* Win32-building support via mingw
* SMT-LIB get-model output now is easier to machine-parse: contains (model...)
* user patterns for quantifier instantiation are now supported in the
  SMT-LIBv1.2 parser
* --finite-model-find was incomplete when using --incremental, now fixed
* the E-matching procedure is slightly improved
* Boolean terms are now supported in datatypes
* tuple and record support have been added to the compatibility library
* driver verbosity change: for printing all commands as they're executed, you
  now need verbosity level >= 3 (e.g., -vvv) instead of level 1 (-v).  This
  allows tracing the solver's activities (with -v and -vv) without having too
  much output.
* to make CVC4 quieter in abnormal (e.g., "warning" conditions), you can
  use -q.  Previously, this would silence all output (including "sat" or
  "unsat") as well.  Now, single -q silences messages and warnings, and
  double -qq silences all output (except on exception or signal).