HISTORY

Prehistory
----------

We designed the Mercury execution algorithm in October 1993. We started
working on a Mercury compiler in December 1993. Semantic analysis
started working around May 1994. We started generating code around
August 1994; we started work on optimizations very soon after. The
compiler successfully compiled itself on 24 February 1995.


Mercury 0.1, April 8 1995
-------------------------
Initial beta-test release. 
Very resource-hungry, not very well documented.


Mercury 0.2, April 18 1995
--------------------------
Much better error messages for determinism errors, much
faster compilation, much lower memory requirements for bootstrapping.
The C compilation is much faster and requires much less memory since we
now by default compile to one C function per procedure, but we also
improved the speed of the Mercury compiler itself by nearly 40% by
implementing some library predicates much more efficiently.


Mercury 0.2.5, 1 June 1995
--------------------------
Much better syntax error messages.
Better documentation, now including a library reference manual.
Added a GNU autoconf configuration script.
Ported to IRIX 5.
Added `multidet'.  
Enabled the use of tag bits in combination with conservative garbage
collection (this improved the speed of the compiler by about 20%).
Compile directly to C rather than via the old .mod files, which were
post-processed by a Perl script (improves compilation speed, reduces
disk space requirements, removes dependency on Perl).
Lots of bug fixes.


Mercury 0.3, 18 July 1995
-------------------------
The first public release.
Better type error messages.
Better determinism error messages.
Only recompiles <module>_init.c after `mmake depend', rather than after
anything changes.
Ported to ULTRIX (N.B. - ULTRIX's /bin/sh sucks).
Avoid saving variables on the stack before negated contexts.
Don't embed label names as strings in the executable.
A few other efficiency improvements.
Lots of bug fixes.
Made the rule for `mmake clean' less reckless (don't do `rm -f *.c').
Rationalized the options to `mc'.  Implemented a couple of new ones.
Added a symbol demangler to improve linker error messages.
Made very significant improvements to the documentation.
Added a "Prolog to Mercury transition guide".


Mercury 0.4, 14 September 1995
------------------------------

* Higher-order predicates and lambda expressions are now implemented.
  (This means that `call/{1,2,3,4}' and `solutions/2' are now usable;
  unfortunately call/{5,6,...} are still not yet implemented.)
* Unique modes are now partially implemented (but don't use them
  for anything except I/O, as the implementation is not yet complete).
* Partially instantiated modes are now closer to being fully
  implemented.
* The installation process is more standard (basically
  just `configure; make; make install').
* Autoconfiguration is a bit more robust.
* `msc' and `mnc' now produce somewhat smaller object files.
* Error and warning messages are a little better in some cases.
* Fixed a few code generation bugs.
* Ported to DEC Alpha/OSF and BSDI BSD/386.
* We've improved the efficiency of the 386 port by about 70%.
  (50% because asm_fast.gc mode now works on the 386, the rest
  due to better optimization).
* We generate better code for calls to `\='.
* We generate better code for `compare/3'.
* A few other new optimizations.
* The profiler now works (see the documentation in the Mercury
  User's Guide).
* Some new library predicates, including `string__format'
  (like C's sprintf).
* `set__join/2' has been renamed as `set__power_union/2'.
* `list__sort/2' has been renamed as `list__sort_and_remove_dups/2'.
* There is a new `list__sort/2' which does not remove duplicates.


Mercury 0.5, 15 Febuary 1996
----------------------------

* We now support committed choice nondeterminism in a logical and declarative
  fashion, using the new determinism categories `cc_nondet' and `cc_multi'.
  Like `nondet' and `multi' respectively, they specify that a predicate
  may have more than one solution, but they convey the additional
  assertion that the predicate will only be used in contexts in which
  only one solution is needed.  The compiler will check that all uses
  of the predicate satisfy this requirement.  Having proven the
  assertion to be correct, the compiler can then generate much more
  efficient code for the predicate.  By pushing pruning inwards, the
  compiler can often avoid creating choice points at all.

* We now check for backtracking over unique modes.
  (This may potentially break some programs using unique modes in ways
  that the compiler can't prove are safe.  In such cases, replacing
  `multi' with `cc_multi' should solve the problem.  If you have any
  trouble with this, we'll be happy to help you.)
  We have also added "mostly unique" modes, which provide support
  for backtrackable destructive update.
  See the Mercury Language Reference Manual.

* We now provide genuinue arrays with destructive update.
  See the library module `uniq_array'.  (Warning: this has not had
  much testing.  The interface is not yet stable.)

* We now support interfacing to C code.
  See the documentation in the Mercury Language Reference Manual.

* There is now an `inline' pragma which you can use as a hint to the
  compiler to inline a particular predicate.

* We've ported the system to ULTRIX (thanks to Gertjan van Noord
  and especially Eero Pajarre).

* We now support shared libraries for IRIX 5.

* We now allow the use of compilers other than gcc -
  see the user's guide for details.
  We don't recommend the use of compilers other than gcc,
  since the inability to use gcc's special features will
  most likely lead to much less efficient code.

* To complement our source distribution, we now also provide binary
  distributions for a variety of platforms.  Installation should be
  quick and easy.

* Various other minor improvements:
  - In portable C mode, we now generate better code for loops.
  - We've made a few other minor improvements in the generated code.
  - Unary plus and minus are now implemented.
  - Updated the documentation to reflect changes in unique modes,
  - Corrected a lot of typos in the documentation.
  - Fixed quite a few bugs.

* Parts of the library module `std_util' have been moved into separate
  modules `assoc_list' and `bool'; if you have existing code which
  used those parts of `std_util', you may need to add `import_module'
  declarations to import `assoc_list' and/or `bool'.


Mercury 0.6, 2 August 1996
--------------------------

* We now provide preliminary support for type and mode inference.
  
  The `:- pred' and `:- mode' declarations are now optional for
  predicates that are local to a module; the compiler will infer
  the types and modes automatically.

  This support is not yet complete, and so type and mode inference are
  not enabled by default.  They can be enabled using the `--infer-types'
  and `--infer-modes' options.  The limitations of the current
  implementation are: (1) type inference loops for certain very rare
  type-incorrect programs; (2) mode inference doesn't support
  reordering; (3) there are some modes which the current mode inference
  algorithm is not capable of inferring.

  Note that omitting type and mode declarations can significantly
  reduce the quality of the compiler's error messages; if you have
  trouble understanding an error message, then it is a good idea to add
  explicit type and mode declarations.

* We now support functional syntax.

  Functions can be declared with `:- func' declarations,
  and defined using equations or conditional equations,
  in a similar manner to the way predicates are declared
  with `:- pred' declarations and defined using facts and rules.
  Terms can contain function calls and if-then-elses.
  For example:

	:- func sum(list(int)) = int.	
	sum([]) = 0.				% unconditional equations
	sum([X|Xs]) = X + sum(Xs).		% using function calls

	:- func max(int, int) = int.
	max(X, Y) = Max :-			% conditional equation
		(X >= Y -> Max = X ; Max = Y).

	:- func min(int, int) = int.
	min(X, Y) = (if X >= Y then X else Y).	% unconditional equation
						% using if-then-else expression

  By default, functions are assumed to have a single det mode with
  all arguments input and the result output, but you can override
  this default by supplying explicit mode declarations; for example,
  this allows you to use functions in a backwards mode to compute the
  function inverse. 

  Zero-arity functions can be used to define constants.

	:- func pi = float.
	pi = 3.14159265359.

  We also support higher-order functions and function lambda expressions.
  See the Mercury Language Reference Manual for details.
  
  The support for functions is not quite complete; there is one minor
  limitation and one major one.  The minor limitation is that the C
  interface does not yet support Mercury functions.  (Fortunately there
  is an easy work-around - since the C interface does support predicates,
  you can just make your Mercury function call a Mercury predicate.)
  The major limitation is that there is currently no support for
  debugging programs using functional syntax; obviously using a Prolog
  system won't work, since Prolog doesn't support functions.

* We now support overloading of predicates (and functions) with the
  same name and arity defined in different modules. 
  
  Previously, an explicit module qualifier was required to resolve the
  ambiguity; now, the typechecker will use the types to resolve the
  ambiguity, if possible.  (Note that you cannot define more than one
  predicate with the same name and arity in the same module.  Allowing
  that would add considerable complexity to the syntax, and would be
  of arguable utility, so we do not anticipate lifting that restriction.)

* We now support defining types with the same name in different modules.

  Previously this resulted in multiply defined symbol errors in certain
  circumstances, e.g. when profiling.

* We have removed the limitations on the number and order of arguments in
  higher-order predicate calls.

* Support for floating point is much improved.
  
  The above-mentioned support for functional syntax and overloading
  have enabled major improvements in the interface used for floating
  point.  You can now use the usual arithmetic and comparison
  operators, rather than the cumbersome builtin_float_plus (etc.)
  predicates that were used previously.  We have also improved code
  generation for floating point operations, by avoiding many
  unnecessary boxing/unboxing operations, and by making the
  `--static-ground-terms' optimization apply also to floating point
  constants.  These two optimizations improved performance on the
  realistic "pseudoknot" benchmark by nearly a factor of four.
  (There's still plenty of room for performance improvements, however.)

* We now support reverse mode arithmetic.

  This means that a goal such as `A is B + C' can be used not only to compute
  A from B and C, but also to compute B from A and C, or to compute C from
  A and B.

* We have added some new compiler options to simplify the choice of which
  optimization options to enable.

  - You can now use `-O<n>' to select an optimization level between -1 and 6.
    The default level is `-O2'; if you want to minimize compilation
    time, compile with `-O0', which disables all optimizations except those
    that actually improve overall compilation speed.

  - You can now use `--optimize-space' to select optimization for space,
    instead of optimization for time (which is the default).

* We have continued to improve the compiler's optimization.

  As well as the above-mentioned improvements to float-point code generation:

  - We now specialize calls to higher-order predicates within the same module
    in the case when the higher-order arguments have known values.
    This optimization is enabled by the `--optimize-higher-order' option.

  - We now specialize calls to predicates within the same module which have
    unused arguments.  This often happens for polymorphic predicates, since
    the compiler introduces type_info arguments which are often unused.
    This optimization is enabled by the `--optimize-unused-args' option.

  - The `--inlining' option now governs the settings of three separate options.
    One, `--inline-simple', reproduces the previous behavior of `--inlining':
    it inlines procedures whose definition is simple (e.g. a conjunction of
    builtins). Another, `--inline-single-use', tells the compiler to inline
    all procedures that are called exactly once. The compiler can also
    inline procedures called more than once as long as they are not too
    big; the argument of the option `--inline-threshold' sets a limit
    on the size of the procedure definition (roughly in terms of the number
    of logical connectives it has) multiplied by the number of calls to
    the predicate.

  - There's a new option `--optimize-dead-proc' option to eliminate unused
    procedures within a module.  This is useful even if the original source
    code didn't contain any unused procedures, since inlining and code
    specialization can make a procedure unused even if there original source
    had calls to that procedure.

  - There's a new option `--split-c-files' which causes the compiler to put
    each C function in its own C file, so that the linker can link in only
    what is used, and a new Mmake target `foo.split' for
    building a version of `foo' compiled with `--split-c-files'.
    (`--split-c-files' has much the same effect as `--optimize-dead-proc',
    except that it works globally, not just within a module.)
    On platforms for which we don't support shared libraries, installing
    a split version of the Mercury library fixes the problem of dumb Unix
    linkers dragging in nearly the entire library even if most of it is
    unused, and so reduces the size of a hello world program from >400k
    to around 120k.

  - The code generator generates special code for dense switches in
    which all the output variables are constant terms.  Instead of
    generating dense jump tables, it puts the answers in static constant
    arrays, and retrieves them using array indexing, avoiding
    an expensive jump and reducing code size.

  - The code generator now emits better code for constructing deeply nested
    terms, and avoids some unnecessary register shuffling.

  - The value numbering optimization now processes code sequences
    containing several heap allocations.

  - The `--pred-value-number' option now works.  If it is given, and
    value numbering notices that a value is available from a location
    that is faster to access than the one from which another code
    sequence retrieves the value, this other code sequence will be
    reoptimized taking this into account.

* We now support a C-to-Mercury interface, ie. we allow C code to call
  Mercury predicates, using a new `pragma export' declaration.
  (Unfortunately, this is not yet documented.  There is however a
  fairly detailed and reasonably well-documented example in the
  samples/c_interface/c_calls_mercury directory.)

* We have added a little bit of inline assembler code for the Alpha so
  that we can support the use of gcc non-local gotos and asm labels.
  This improved both code size and execution speed for the Alpha port
  by about 20-25%.

* We have ported the Mercury implementation to RS/6000 systems running AIX.
  (Thanks to Andreas Kuehlmann.)

* We have made a few changes to the Mercury standard library.
  The changes are listed here, but see the Mercury Library Reference Manual
  for details such as documentation on the new predicates.

  - The getopt library is now more flexible.  It can handle command
    line switches (such as `-O2') that affect the values of many
    options, and it can handle long options that specify a value after
    an equal sign, in the GNU style (e.g. `--optimization-level=2').

  - We have added a few new predicates using higher order facilities:
	list__map/3, list__filter/3, list__filter/4, list__foldl/4,
	list__foldr/4, list__sort/4 and list__merge/4 in list.m and
	maybe_pred/3 in std_util.m. 

  - There are a couple of new all-solutions predicates in std_util.m:
    solutions_set/2 and unsorted_solutions/2. 

  - We have added some additional predicates for handling association lists:
    assoc_list__search/3 and assoc_list__remove/4.

  - There are a few new predicates for converting floats to ints:
    float__ceiling_to_int/2, float__floor_to_int/2
    float__round_to_int/2, and float__truncate_to_int/2.

  - There are quite a few changes to the graph module.  The interface has been
    made more consistent with the rest of the library.  The predicate
    graph__lookup_node/3 has been replaced by two predicates:
    graph__search_node/3 which is nondet and returns all the nodes with
    matching data, and graph__find_matching_nodes/3 which is det and
    returns all the nodes with matching data.

  - We have renamed the varset__lookup predicates to varset__search in order to
    conform to our general naming convention.

  - We have removed the (undocumented) library predicate list__map_maybe/3.

  - The set module is now implemented using sorted lists rather than
    unsorted lists.  (The interface is still the same.)  The old
    unsorted lists representation is still available, in the
    set_unordlist module.


Mercury 0.7, 15 August 1997
---------------------------

* The Mercury language now supports higher-order syntax.

  You can now write `P(X)' as an alternative to `call(P, X)'
  or `F(X)' as an alternative for `apply(F, X)'.

* Module qualifiers are now optional.

  You can use just plain `write_string' rather than `io__write_string'.

* There is a new `:- use_module' directive.

  This is the same as `:- import_module', except all uses of the imported
  items must be explicitly module qualified.

  More changes to the module system are expected in the future,
  possibly including changing the module qualifier operator to `.'.
  Currently either `:' or `__' can be used as module qualifiers,
  but we advise you to stick with using only `__' rather than `:',
  to avoid problems in the future if we do change the module
  qualifier to `.'.

* We've improved the C interface.

  The C interface now handles Mercury functions properly --
  previously it only handled predicates, not functions. 
  Also, exporting semidet predicates or functions to C now works.
  We've improved the documentation, and we've included some examples
  of how to use the C interface to interface with C++.
  We also now support `main' being defined in C rather than in Mercury.

  See samples/c_interface for examples of all of the above.

* We now support cross-module optimizations.

  The `--intermodule-optimization' option enables cross-module inlining
  and cross-module specialization of higher-order predicates.
  Also `--intermod-unused-args' enables cross-module elimination of
  unused input arguments.

* We've continued to improve the quality of the code we generate.

  We now use a more efficient argument-passing convention, and the code
  we generate for polymorphic predicates uses a more efficient "type-info"
  representation than previous versions. 

  (Note that this means code generated by Mercury 0.7 is not compatible
  with code generated by earlier versions, so you will need to
  recompile any existing Mercury object files or libraries when you
  install the new version.)

  We handle floating point code a bit better.  We don't box floating
  point values on 64-bit architectures anymore, and on 32-bit
  architectures we do a better job of avoiding unnecessary box/unbox
  operations.  We also make some use of floating point registers for
  holding temporary values.

  We've made several improvements to the code generator that result in
  better code in common situations.

  There's also a new optimization option, `--inline-alloc', which can
  speed up code that does a lot of memory allocation by inlining the
  GC_malloc() function.  (This option is also enabled by `-O6'.)

* We now support ELF shared libraries on Linux.

  See README.Linux for details.

  Note that using shared libraries is not yet the default,
  so if you want to take advantage of this, you must explicitly
  enable it as described in README.Linux.

* We have added support for very large tables of facts.

  See the documentation for `pragma fact_table' in the
  "implementation-dependent pragmas" section of the Mercury
  Language Reference Manual.

* We have fixed quite a few bugs.

  Mode inference now works a little bit better. 
  
  We now allow a function of arity N to coexist with a predicate of
  arity N+1.

  The Mercury `char' type is now 8-bit clean (previously, "for
  compatibility with NU-Prolog" we only supported 7-bit characters).

* The `mc' script has been renamed `mmc'.

  This was done to avoid name clashes with the Midnight Commander
  and the Modula Compiler.

* We've added `man' pages.

  The documentation now includes Unix-style `man' pages for
  most of the development tools, including mmake, mmc, mgnuc, ml,
  and mprof.  These supplement the existing documentation in the
  Mercury User's Guide.

  Most of the information in the man pages is also available using
  the standard `--help' option.

* We've improved the compiler's diagnostics a bit.

  Some of the compiler's error messages are a bit more informative, and
  it catches some errors that previously it missed (such as specifiying
  modes in some but not all of the arguments of a `:- pred' declaration).

* We have made quite a few changes to the Mercury standard library.

  The changes are listed here, but see the Mercury Library Reference Manual
  for details such as documentation on the new predicates.

  - The std_util.m module now contains functions and predicates for
    traversing and constructing terms of arbitrary type, and for
    accessing types at runtime.

    	+ For traversing terms: 
    		Functions argument/3, det_argument/3, functor/3,
		and predicate deconstruct/4.  These are similar to
		Prolog's arg/3, functor/3, and '=..'.

	+ For constructing terms:
		Functions num_functors/1, construct/3 and
		predicate get_functor/5.

	+ For accessing and constructing types:
		Functions type_of/1, type_ctor/1, type_args/1,
		type_ctor_name/1, type_ctor_arity/1, make_type/2,
		and predicates type_ctor_and_args/3 and
		type_ctor_name_and_arity/3.

    There are also some new functions for accessing values of the
    universal type `univ', namely univ/2 and univ_type/1.

  - There is a new module called `prolog' which contains some predicates that
    may be useful for compatibility with Prolog: arg/3, functor/3,
    `=:=', `=\=', `==', `\==', `@<', `@>', `@=<', `@>='.  We plan to
    eventually move the definitions of cut (`!') and `is' here too.
    
  - We've finally implemented generic input-output predicates,
    namely io__print/3, io__write/3, and io__read/3, using the the
    functions and predicates described above.  These can read or write
    data of any type.  We've also added io__nl/3 to print a newline.
    Together with the change to make module qualifiers optional, these
    changes make performing output quite a bit simpler; it's nice to be
    able to write `print("Foo = "), print(Foo), nl'.

  - We've also added generic predicates io__write_binary/3 and
    io__read_binary/3, for doing binary I/O on values of any type.
    (The current implementations actually just call io__read/3 and
    io__write/3 respectively, though, so they're not maximally efficient.)

  - The predicates term_to_type/2 and type_to_term/2, which convert
    values of any type to or from type `term', are now implemented.

  - We have a new module called benchmarking.m to make benchmarking easier.
    The predicate report_stats, which used to be in std_util, is now
    in this module.

  - The interface to the relation.m module has been changed extensively.
    Elements must now be explicitly added to the domain of the relation,
    using relation__add_element/4, and relation operations such as
    relation__add are now performed on relation_keys.  There are also
    four new operations which convert elements to relation_keys and
    vice versa:
	relation__search_element/3, relation__lookup_element/3,
	relation__search_key/3, and relation__lookup_key/3

  - We changed the order of the arguments to set_bbbtree__subset,
    for consistency with the order in set__subset and elsewhere.
    We also changed the implementation of set__subset and
    set_ordlist__subset to match the behaviour specified in the
    documentation.

  - We made some extensive additions to bag.m to include the standard set
    operations (union, intersection, subtraction), and some other predicates
    for manipulating bags.  We also changed bag__contains/2 (swapped the 
    arguments), and bag__remove (now semidet) to be consistent with set.m 
    and map.m. 

  - There are two new predicates io__tmpnam and io__remove_file,
    with semantics similar to the ANSI C functions tmpnam() and remove().

  - There are new predicates int__max_int, int__min_int, int__bits_per_int,
    char__min_char_value, and char__max_char_value, with semantics similar
    to INT_MAX, INT_MIN, (CHAR_BIT * sizeof(int)), CHAR_MIN, and CHAR_MAX
    in ANSI C (respectively).

  - We've added list__merge_and_remove_dups/4 and list__sort_and_remove_dups/4
    to complete the set of list__merge and list__sort operations.

  - We've added io__write_list/5 and io__write_list/6; these predicates write
    lists using a user-specified procedure to write the elements and separating
    the elements with a user-specified separator string.

  - We've added io__read_file/{3,4} and io__read_binary_file/{3,4} which read
    whole files (until error or eof).

  - We've added a double accumulator version of list__foldl/4 called
    list__foldl2/6, which is a convenient generalisation for accumulators
    that also do I/O.  Also, we've added list__map_foldl/5, which is an
    amalgam of list__map/3 and list__foldl/4.

  - We've added a new constructor `maybe_string' to getopt's option_data
    type, for parsing optional string-valued command-line arguments. 
    See library/getopt.m for details.  Also added to getopt are some
    missing option-lookup predicates: getopt__lookup_accumulating_option/3
    and getopt__lookup_maybe_string_option/3.

  - We've added string__foldl to the library.  It has the same semantics as
    (string__to_char_list(String, Chars), list__foldl(Pred, Chars, Acc0, Acc))
    but is implemented more efficiently.

  - We've cleaned up the handling of integer division and modulus/remainder.
    Previously the semantics of `//' and `mod' were not really well defined.
    The semantics of `//' and `mod' have now been clarified and there are
    new functions `div' and `rem'.  `//' truncates towards zero, and `rem'
    is remainder with respect to `//', whereas `div' truncates towards minus
    infinity, and `mod' is remainder with respect to `div'.

  - The old array.m module has been renamed bt_array.m (short for
    "backtrackable array", or "binary tree array"), and uniq_array.m
    has been renamed array.m.  The interfaces of both modules have been
    extended to make them closer to each other.

    The following predicates have been added to array.m (formerly
    uniq_array.m):

	+ array__shrink/3: this is similar to array__resize/4 except
	  that it's designed for cases when you only want to make an
	  array smaller, so you don't have to supply a filler element.

	+ array__min/2, array__bounds/3: find the lower bound or both
	  bounds (respectively) of an array.  (In this implementation,
	  the lower bound is always 0.)

    The following predicates have been added to bt_array.m (formerly
    array.m):

	+ bt_array__min/2, bt_array__max/2, bt_array__size/2: find
	  the lower bound, upper bound and size of a bt_array
	  respectively.
	
	+ bt_array__in_bounds/2: check if an index is within the
	  bounds of a bt_array.
	
	+ bt_array__semidet_set/4: the semidet version of bt_array__set/4.

        + bt_array__from_list/3: a replacement for bt_array__from_list/2,
	  which has been removed.  The extra argument is the lower bound
	  for the new bt_array.

	+ bt_array__shrink/4: analogous to array__shrink/3.

	+ bt_array__resize/5: a replacement for bt_array__resize/4.  There
	  was a design flaw in the previous interface, in that if the
	  array increased in bounds, the extra slots were filled with one
	  particular element from the old bt_array.  The extra argument is
	  the element to use to fill these slots instead.

* There is a new `extras' directory in the distribution that contains
  some additional libraries.  These provide support for the following
  application areas:

  - graphics using Tk and OpenGL

  - arithmetic on complex and imaginary numbers

  - processing HTML forms using the CGI interface.


Mercury 0.7.2, 13 October 1997
------------------------------

We have split the distribution into two parts, a `core' part and an
`extras' part.  We still recommend that people get both parts.

Changes to the Mercury language:
********************************

* We have added support for constraint handling.

  To support constraint handling, we've made the mode system a bit
  more flexible.  There is a new inst `any' for variables whose value
  is unknown but which may have constraints on them. 

  The support for `any' insts is not 100% complete; in particular, we
  do not support passing values of inst `free' where values of inst
  `any' are expected, so sometimes you have to explicitly call a predicate
  to initialize a free variable to inst `any'.  Also the Mercury language
  reference manual does not yet contain any documentation on `any' insts.

  The `extras' distribution includes packages for doing constraint
  solving on (a) floating point numbers and (b) terms containing
  Prolog-style variables.  See below.

* The C interface now includes generalized trailing support.

  The compiler has a new set of grades `*.tr' (e.g. `asm_fast.gc.tr')
  which provide support for trailing.  They could be used by predicates or
  functions defined using the C interface to perform such things as
  constraint solving, backtrackable destructive update, or even automatic
  unwinding of database transactions on backtracking.  See the
  documentation in the "Trailing" section of the Mercury language
  reference manual (it's at the end of the "C interface" section,
  which is in the chapter on "Pragmas").

* It is now possible to stop the compiler from optimizing "impure"
  Mercury code inappropriately.

  This is accomplished by declaring impure predicates to be impure,
  allowing the compiler to treat them cautiously.  The compiler tracks
  impurity, and requires all impure predicates, and calls to them, to
  be declared.  For more information, see "Impurity" section of the
  "Pragmas" chapter of the Mercury Language Reference Manual.

* We now support user-defined equality predicates.

  See the Mercury Language Reference Manual for details.

  However, until we have support for type classes (coming soon :-),
  you will probably run into trouble if you try to use compare/3,
  write/1, functor/2, etc., on a type with user-defined equality.
  Hence we recommend that this feature should not yet be used.
  Because of this, we haven't bothered to document the
  rationale or use for user-defined equality predicates
  (though rest assured that when we do have type classes,
  this feature will indeed be useful).

* We have introduced new syntax to allow higher-order predicate expressions
  to use DCG notation.

  For details, see the "Data-terms" section of the "Syntax" chapter
  and/or the "Creating higher-order terms" section of the "Higher-order"
  chapter in the Mercury Language Reference Manual.


Changes to the Mercury standard library:
****************************************

* We have rewritten the `store' module to use unique modes.

  The `store' module provides a declarative interface to mutable variables
  with destructive update.

* The library predicate unsorted_aggregate/4 in std_util.m
  now interleaves calls of the aggregation predicate with
  the generation of solutions, rather than first finding all
  solutions and then aggregating them.  This allows you
  to print out solutions as they are found, for example.

* We have added a few new predicates, namely list__takewhile/4,
  bag__to_list/2, and varset__new_named_var/4.

* We have changed the interface to lexer__get_token_list to use a more
  efficient representation of lists of tokens. The functionality is
  unchanged.

* We have fixed a problem where io__call_system/4 was not returning the
  the exit code of the invoked command on some operating systems.

* We have fixed a bug in relation__rtc/4.

* We have added the predicate queue__delete_all/3.

* Map (and tree234) have 2 new predicates: map__foldl which is
  analogous to list__foldl, and map__map_values which is analogous
  to list__map.

* We have added integer.m, which implements arbitrary precision integers,
  and rational.m, which implements arbitrary precision rational numbers.


New library packages in the `extras' distribution:
**************************************************

* We have added a CLP(R) interface.

  The new library package `cfloat_lib', in the extras/clpr directory,
  is a Mercury interface to the CLP(R) constraint solver.  The module
  `cfloat' defines a type `cfloat' for constrained floating point numbers,
  together with the usual arithmetic operators (+, -, *, /, <, >, =<, >=)
  as well as some non-linear constraint functions (abs, min, max,
  sin, cos, arcsin, and arccos).  The module `dump' provides I/O predicates
  for printing out constraints.

  Note that since `cfloat' is a different type than `float', you
  have to use the `==' operator provided in this package rather
  than `=' if you want to unify a cfloat with a float.
  
  We don't yet support any equivalent to SICStus Prolog's
  call_residue/3 or the three-argument version of CLP(R)'s dump predicate.

  But apart from that, it all works nicely.  And even though we support
  equivalents to such nasty non-logical meta-programming constructs
  as CLPR's `dump' primitive, we still manage to preserve referential
  transparency -- the interface provided is a completely pure declarative
  interface.

* We have added some support for Prolog-style variables and coroutining.

  The module extras/trailed_updated/var.m provides a type `var(T)'
  which is a Prolog-style variable that holds a value of type T.
  These variables can have the new inst `any' described above.
  There's also an implementation of freeze/2, for coroutining
  (dynamic scheduling).  The extras/trailed_update/samples subdirectory
  has an example of the use of freeze/2 to solve the N-queens problem.

* We have added library modules for backtrackable destructive update.

  See the new modules `tr_array' and `tr_store' in the extras/trailed_update.
  These are versions of `array' and `store' that use trailed backtrackable
  destructive update.  The extras/trailed_update/samples subdirectory
  has an example of the use of tr_store to provide a reasonably efficient
  meta-interpreter.

* We have added an interface to ODBC databases in extras/odbc. 

  Thanks to the people from Mission Critical, in particular Renaud Paquay,
  for providing the original version. 


Changes to the Mercury compiler:
********************************

* We have added support for termination analysis.

  For details, see the "Termination analysis" subsection of the
  "Implementation-dependent pragmas" section of the "Pragmas" chapter
  of the Mercury Language Reference Manual.

  This implementation is experimental, but our tests show that it is
  capable of proving the termination of most predicates and functions
  in real programs.

  The current implementation of termination analysis depends on the
  third-party package lp_solve. This is package is available from
  <ftp://ftp.es.ele.tue.nl/pub/lpsolve>; it is also included in the
  lp_solve subdirectory of the Mercury source distribution. Note
  that the copyright of lp_solve includes substantial restrictions.

  Details of the analysis is available in "Termination Analysis for
  Mercury" by Chris Speirs, Zoltan Somogyi and Harald Sondergaard. In P.
  Van Hentenryck, editor, "Static Analysis: Proceedings of the Fourth
  International Symposium", Lecture Notes in Computer Science. Springer,
  1997.  A longer version is available for download from
  <http://www.cs.mu.oz.au/publications/tr_db/mu_97_09.ps.gz>.

* We have made it easier to use different compilation models ("grades").

  The Mercury compiler (mmc), the Mercury front-end to GNU C (mgnuc),
  and the Mercury linker (ml) now figure out which grade to use based
  on the options specified.  This means that for example to enable
  profiling, you can just compile and link with `--profiling', rather
  than having to specify grade `asm_fast.gc.prof'.

  Attempts to mix object files compiled with different grades should now
  result in errors at link time rather than undefined behaviour.

* We have improved the C interface.

  We now handle the case when `main' is defined in C rather than in Mercury
  slightly more cleanly -- there are functions mercury_init()
  and mercury_terminate() for initializing and terminating the
  Mercury runtime.  See runtime/init.h for documentation of the functions,
  and see samples/c_interface/simpler_c_calls_mercury for an example of
  their use.

* The compiler does a better job of constant-propagation optimization.

* We have fixed a few minor bugs.


Mercury 0.7.3, 1 November 1997
------------------------------

This release is primarily a bug-fix release.  The problems fixed
include installation problems on Windows, some problems with the
profiler, and compatibility with GNU Make versions >= 3.76.
But as well as bug fixes, there are a few minor improvements:

* The profiler now allows you to merge profiling data from multiple runs.

  There's a new script `mprof_merge_runs' to support this.
  See the "Profiling" section of the Mercury User's Guide,
  or the man page for `mprof_merge_runs'.

* Termination analysis no longer uses the `lp_solve' package,
  so we have removed it from the distribution.
  
  This avoids some portability problems and some copyright issues
  (the `lp_solve' package had a quite restrictive license).

* We've fixed one of the limitations: unique mode declarations
  no longer have to precede non-unique mode declarations.


Mercury 0.7.4, 1 November 1997
------------------------------

This release just corrected a couple of bugs in the binary
distribution for 0.7.3.


Mercury 0.8, 18 November 1998
-----------------------------

Changes to the Mercury language:
********************************

* The type system now includes support for Haskell-style type classes.

  Type classes let you specify an interface and then provide multiple
  different implementations of that interface.  They're similar to
  abstract base classes in C++ or "interfaces" in Java.
  See the "Type classes" chapter of the Mercury Language Reference Manual
  for details.

  Unlike Haskell 1.4, Mercury supports multi-parameter type classes,
  but we do not (yet) support constructor classes, and nor do we
  support default methods.

* Mode inference can now infer "mostly-unique" modes as well as
  "unique" modes.

* You can now declare both committed-choice ("cc") and backtracking (non-cc)
  modes for the same predicate.
  
  Determinism analysis will pick the appropriate one to use for each
  call based on the context.

* The module system now includes support for sub-modules.

  The aim of this extension is twofold.  One aim is to provide more
  fine-grained encapsulation control: nested sub-modules within a
  single source file provide a convenient method for encapsulating
  units smaller than a source file.  The other aim is to provide better
  support for structuring large software packages that consist of many
  source files.  Sub-modules can be defined in separate files, with
  separate compilation, which means that you can also use this feature
  to combine a group of existing Mercury modules into a single logical
  package, with proper namespace control and encapsulation.

  See the "Modules" chapter of the Mercury language reference manual
  for details.

* We have made more improvements to the C interface.

  The C interface now includes support for defining procedures
  that can have multiple solutions (i.e. those whose determinism
  is `nondet' or `multi') in C.

  Also there's a new declaration, `pragma import', which is a bit
  like the existing `pragma c_code' declaration except that
  instead of giving a C code fragment, you just give the name
  of a C function.  `pragma import' is like the inverse of the
  existing `pragma export' declaration.

* We have added support for automatic tabling (memoization).

  See the "Tabled evaluation" subsection of the "Implementation-dependent
  pragmas" section of the "Pragmas" chapter of the Mercury language
  reference manual.

* We have added (tentative) support for exception handling.

  The interface to exception handling is actually via an `exception.m'
  library module rather than a new language construct.  
  For now, this module is located in the `extras/exceptions'
  directory, which is part of the `mercury-extras' distribution,
  but our intent is to eventually migrate this into the Mercury
  standard library if experience with its use proves positive.

  The exception handling interface uses committed choice nondeterminism
  to avoid some semantic problems with previous exception handling
  proposals.

  See the documentation in the interface of `exception.m' for details.

Changes to the Mercury standard library:
****************************************

* There is also a new builtin function promise_only_solution/1,
  for calling `cc_multi' or `cc_nondet' code from `det' or `semidet'
  procedures.  See the "builtin" chapter of the Mercury Library
  Reference Manual for details.

* The getopt module now supports a new type of option data, namely
  `maybe_int(maybe(int))', to allow optional arguments with integer values.
  There is also a new corresponding lookup predicate,
  getopt__lookup_maybe_int_option/3. 

  See the "getopt" chapter of the Mercury Library Reference Manual for details.

* Support for memory profiling: new predicates report_full_memory_stats/0
  in benchmarking.m and io__report_full_memory_stats/2 in io.m.

  See the "benchmarking" chapter of the Mercury Library Reference Manual
  for details.

* The types `term', `var', `var_supply' and `varset' are now polymorphic.
  This allows one to distinguish between terms, etc. denoting different kinds
  of things by giving them different types. The new coercion predicates
  listed below allow one to coerce terms, etc between types.

  The monomorphic versions of these have been retained as equivalences
  to the polymorphic ones with the type variable instantiated to a dummy
  type `generic'.

* Miscellaneous new predicates.

  The Mercury standard library now includes the following new predicates:

	  bag__det_remove_list/3
	  bag__least_upper_bound/3
	  bag__remove_list/3
	  det_univ_to_type/2
	  eqvclass__same_eqvclass_list/2
	  io__read_line_as_string/{3,4}
	  list__take_upto/3
	  map__det_insert_from_assoc_list/3
	  map__det_intersect/5
	  map__det_union/5
	  map__intersect/4
	  map__sorted_keys/2
	  map__to_sorted_assoc_list/2
	  map__union/4
	  relation__add_values/4
	  relation__compose/3
	  relation__from_assoc_list/2
	  set__count/2
	  set_ordlist__count/2
	  store__new_cyclic_mutvar/4
	  term__coerce/2
	  term__coerce_var/2
	  term__coerce_var_supply/2
	  varset__coerce/2
	  varset__select/3

  In addition, there are four new system constants added to the float
  library module, float__radix, float__mantissa_digits, float__min_exponent
  and float__max_exponent.  There are also predicate equivalents for these.

  Also the old relation__to_assoc_list/2 predicate has been renamed as
  relation__to_key_assoc_list/2; there is a new relation__to_assoc_list/2
  predicate with a different type for the second argument.

  See the Mercury Library Reference Manual for details.

* A few library procedures that have implicit side effects and are thus 
  intended for debugging use only have been declared `impure'.
  You will need to write `impure' before every call to these procedures
  and typically you will need to add a `pragma promise_pure' declaration
  for the callers.

  The predicates affected are report_stats/0 and report_full_memory_stats/0
  in library/benchmarking.m; unsafe_dump/2, unsafe_dump_float/1, and
  unsafe_dump_tableaus/0 in extras/clpr/dump.m; and debug_freeze/3
  and debug_freeze/4 in extras/trailed_update/var.m.

* The interface to the predicate term__compare/4 was found to be error-prone,
  and so we are phasing it out; it is declared with `pragma obsolete'
  in this version, so any use of it will now result in a warning, and
  the predicate will be removed entirely in some future version.

Changes to the Mercury implementation:
**************************************

* We've added a new source-to-source transformation - deforestation.

  Deforestation transforms conjunctions to avoid the construction
  of intermediate data structures and to avoid multiple traversals
  over data structures. Deforestation is enabled at optimization level
  `-O3' or higher, or by using the `--deforestation' option.

* The compiler can now perform type specialization.

  Type specialization removes the overhead of polymorphic code, including
  code which uses type classes. The disadvantage is increased code size.
  Currently we do not perform inter-module type specialization.
  Type specialization is enabled by using the `--type-specialization' option.

* We've added support for "transitive" inter-module analysis.

  With the previous support for inter-module optimization, when
  analysing a module, the compiler could make use of information
  about the modules that it imports directly, but not about
  modules that are imported indirectly.  "Transitive" inter-module
  analysis gives the compiler information about indirectly
  imported modules.

  However, currently this is only used for termination analysis;
  optimizations such as inlining still use only ordinary inter-module
  analysis, not transitive inter-module analysis.

* Array bounds checking can now be disabled.

  To disable array bounds checking, you must compile with
  `--intermodule-optimization' enabled and you must also
  define the C macro ML_OMIT_ARRAY_BOUNDS_CHECKS (e.g. by using
  `MGNUCFLAGS=-DML_OMIT_ARRAY_BOUNDS_CHECKS' in your Mmakefile). 

* Domain checking for higher mathematical operations can now be disabled.

  To disable domain  checking, you must compile with
  `--intermodule-optimization' enabled and you must also
  define the C macro ML_OMIT_MATH_DOMAIN_CHECKS (e.g. by using
  `MGNUCFLAGS=-DML_OMIT_MATH_DOMAIN_CHECKS' in your Mmakefile). 

  See the Mercury Library Reference Manual for details.

* We've added some primitive debugging support.

  The runtime system now includes a "four-port" style debugger
  (actually with eight ports).
  To use this debugger, you need to build your program with debugging
  enabled, which is normally done using the `--debug' (or `-g') option,
  and then run it using the `mdb' command, e.g. `mdb a.out'.
  Type `h' at the `mdb>' prompt for a list of the available commands,
  or see the "Debugging" chapter of the Mercury User's Guide for further
  details.

* The support for debugging using Prolog now includes support for
  detailed control over how terms are printed out during debugging.

  See the "Using Prolog" section of the Mercury User's Guide for details.
  However, for most purposes we now recommend using the native Mercury
  debugger rather than debugging using Prolog.

* The Mercury profiler has a number of new features.

  The profiler now supports profiling just user time, or profiling
  real (elapsed) time, rather than profiling user + system time.
  We've also added support for memory profiling.

  See the "Profiling" chapter of the Mercury User's Guide for details.

* Profiling should now work on MS Windows.

  To enable profiling on MS Windows, you need to have Sergey
  Okhapkin's latest version of gnu-win32 that includes his patch to add
  support for setitimer().  Sergey's "CoolView" version of cygwin.dll
  is available via <http://miracle.geol.msu.ru/sos/>; his patch will
  probably also be included in the next (b19) release of gnu-win32.
  Note that on Windows, you must use the Mercury runtime system's `-Tr'
  (profile real time) option; profiling just user time or user + system
  time is still not supported on Windows, because to the best of our
  knowledge Windows doesn't provide the necessary system calls.

* Intermediate files can be placed in subdirectories.

  If you use the `--use-subdirs' option to `mmake' or `mmc',
  then they will create the various intermediate files used
  by the Mercury implementation in a subdirectory called `Mercury'
  rather than in the current directory.  (For `mmake', if there
  is already a `Mercury' subdirectory, then this option is the default.)
  This keeps your source directories much less cluttered.

* Mmake has a new variable GRADEFLAGS for specifying options that
  affect the grade (compilation model).

  This means that for example to enable profiling, you can build with
  `GRADEFLAGS = --profiling' in your Mmakefile, rather than having to
  use the more obscure incantation `GRADE = asm_fast.gc.prof'.

* Mmake now supports per-file settings of MCFLAGS and other *FLAGS variables.

  For example, if you want to disable singleton variable warnings just
  for a single module `horrible_code.m', you can just include the line

	  MCFLAGS-horrible_code = --no-warn-singleton-variables

  in your Mmakefile.

* Mmake now warns about variables which are defined but not used.

  To disable this warning, use the `-w-' or `--no-warn-undef-variables'
  option.

* The components of the argument to the `--grade' option and of the `GRADE'
  Mmake variable may now be given in any order. The compiler also has a
  new option `--output-grade-string' which prints the canonical grade string
  for the set of options with which the compiler was invoked.

* Mmake now runs a bit faster, particularly on Windows.

* We've made a few small improvements to the efficiency of the generated code.

* The system has been ported to Linux/PPC.

* The system has been ported to work with version b19 of cygwin32
  (this port has not been tested well, though). 
  See README.MS-Windows for details.

* We've updated to version 4.13alpha2 of the Boehm garbage collector.

* We've made the MERCURY_OPTIONS environment variable somewhat easier to use.

* Mtags is now able to produce tags for type class declarations.  It is
  also able to produce tags files in the extended format supported by
  recent versions of Vim and Elvis.  Do `mtags --help' for more
  information.

* Numerous bug fixes.


Mercury 0.8.1
-------------

This release just corrected some bugs in the binary
distribution for 0.8.


MLDS back-end history
---------------------

We started working on a new back-end for the Mercury compiler in July
1999.  This new back-end, called the MLDS back-end, generates much
higher level C code than original back-end.  The first prototype
compiled "hello world" in September 1999.  The compiler successfully
compiled itself using the MLDS back-end on 12 May 2000.