Mercury version 0.7 released

Fergus Henderson fjh at
Fri Aug 15 02:31:47 AEST 1997

We've been delayed by several hard disk crashes... but at long last...
we are pleased to announce the release of version 0.7 of the Mercury system.

Here is what's new in version 0.7:

* 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 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

    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

  - 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

	+ 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

	+ bt_array__min/2, bt_array__max/2, bt_array__size/2: find
	  the lower bound, upper bound and size of a bt_array
	+ 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.

The Mercury distribution is available via anonymous ftp or WWW
from the following location:


and also should hopefully also be available from the following locations
sometime soon:


There are binary distributions for sparc-sun-solaris, alpha-dec-osf,
and i386-linux, as well as the source distribution.
We may add other binary distributions as they become available.

The Mercury project's home page on the Web is <>.

The Mercury Team <>
Department of Computer Science, The University of Melbourne, Australia

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