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Release 0.12 Notes

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New in release 0.12.2 of the Mercury distribution

New in release 0.12.1 of the Mercury distribution

New in release 0.12 of the Mercury distribution

HIGHLIGHTS

• Infix `.' is now accepted as a module name separator.
• Field access syntax can now be used at the top-level in func and mode declarations and in the head of a clause for a user-defined field access function.
• We now support impure higher-order code.
• We now allow user-defined comparison predicates.
• User-defined equality and comparison predicates for a type are now required to be defined in the same module as the type.
• Experimental support for user-defined constrained types has been added.
• We now support the use of `..' as an infix operator.

Changes to the Mercury standard library:

• We've added several new modules: cord, for sequences with O(1) consing and concatenation, array2d, for two-dimensional arrays, and version_array, version_array2d, version_bitmap, version_hash_table, and version_store, implementing non-unique versions of these types supporting O(1) access for non-persistent use. A new module term_to_xml has been added for converting arbitrary terms to XML documents. Two new modules, set_tree234 and set_ctree234, have been added to provide operations on sets with better worst-case behavior (but worse constant factors) than the current implementation. Ten new modules, svarray, sveqvclass, svmap, svmulti_map, svbimap, svset, svbag, svqueue, svrelation and svvarset now provide more convenient ways to update arrays, equivalence classes, maps, multi_maps, bimaps, sets, bags, queues, relations and varsets in code that uses state variables.
• New procedures have been added to many of the existing standard library modules. Most notably, these include procedures for creating directories and symbolic links, for checking file types and file accessibility, for detecting floating point infinities and NaNs.
• The dir module now handles Microsoft Windows pathnames correctly.

Changes to the Mercury compiler:

• We have added optional support for a new type-accurate garbage collector as an alternative to using the Boehm et al conservative collector.
• Better support for incremental program development: there's two new compiler options, `--allow-stubs' and `--no-warn-stubs', to support execution of incomplete programs.
• There's a new warning option `--warn-dead-procs' for detecting unreachable code.
• It's now easier to use shared libraries on Linux/x86 systems with `mmc --make'.
• A new analysis: `--analyse-exceptions'. The compiler can use the results of this analysis to try and improve some optimizations.

Portability improvements:

• We have made the implementation compatible with gcc 3.4.
• Shared libraries now work on Mac OS X.

Changes to the Mercury debugger:

• Users can now arrange to have the goal and/or some variables printed every time execution arrives at a breakpoint.
• Users can now arrange to associate a condition with a breakpoint. Execution won't stop at the breakpoint if the condition is false.
• Users can now limit the output from stack traces.
• Users can now put breakpoints on unify and compare predicates.
• Users can now save runtime values to files.
• Users can now tell the declarative debugger to trust entire modules or individual predicates or functions.
• The declarative debugger can track the origins of subterms.
• The declarative debugger can now use the divide-and-query search strategy.

Changes to the compiler back-ends:

• Improvements to the .NET CLR back-end.
• Improvements to the Java back-end.
• The cost in disk space of enabling debugging is now much smaller.

Numerous minor improvements to the Mercury standard library. Changes to the extras distribution:

• Added easyx, a new Xlib based graphics library suitable for implementing simple interactive graphical applications.
• Major improvements to the OpenGL binding.
• We've added a binding to GLUT (the GL utility toolkit).
• The OpenGL, GLUT and Tcl/Tk bindings have been ported to Mac OS X.

DETAILED LISTING

• The deprecated support for NU-Prolog style `when' declarations has been removed.
• We have experimental support for user-defined constrained types, as documented in the reference manual section on "Solver types". Variables of a constrained type can have constraints placed upon them before they are instantiated, allowing for various styles of constraint logic programming.
• We now allow user-defined comparison predicates, using the syntax :- type t ---> t where equality is unify_t, comparison is compare_t. See the "User-defined equality and comparison" chapter of the Mercury Language Reference Manual for details.
• User-defined equality and comparison predicates for a type are now required to be defined in the same module as the type.
• Infix `.' is now accepted as a module name separator. Hence it is now possible to write io.write_string and list.member to mean the same thing as io__write_string and list__member, for instance. This has required changing the associativity of `.' from xfy to yfx and from precedence 600 to 10.
• Field access notation can now be used at the top-level in func and mode declarations and in the head of a clause for a user-defined field access function. That is, one can now write

    	:- func a ^ f(b) = c.
  	:- mode a ^ f(b) = c is .
  	A ^ f(B) = ...
  

• Mercury's support for impure code now also includes support for impure higher-order code.

  Specifically, impurity annotations can be used on higher-order types, lambda expressions, and higher-order calls; higher-order terms are permitted to call impure or semipure code provided that they are appropriately annotated as such.

  For details, see the "Higher-order impurity" section of the "Impurity" chapter of the Mercury Language Reference Manual.

• `..' is now accepted as an infix operator. That means a list of successive integers can now be written as X .. Y. For example:

  	1 .. 5 = [1, 2, 3, 4, 5]
  

Changes to the Mercury standard library:

• We've add the function queue.from_list/1 as a synonym for queue.list_to_queue/1, function queue.to_list/1 (and predicate queue.to_list/2) as the converse of queue.from_list/1, queue.put_on_front/2 (and predicate queue.put_on_front/3) to put items on to the front of a queue, queue.put_list_on_front/2 (and predicate queue.put_list_on_front/3) to put a list of items on to the front of a queue, and predicate queue.get_from_back/3 which removes the last element from a queue.
• We've added the function pqueue.from_assoc_list/1 as a synonym for pqueue.assoc_list_to_pqueue/1.
• We've added functions set.from_list/1 and set.from_sorted_list/1 as synonyms for set.list_to_set/1 and set.sorted_list_to_set/1 respectively. Similar additions have also been made to the set_unordlist, set_ordlist and set_bbbtree modules.
• We've added some new higher-order predicates, rbtree.foldl2/6 rbtree.foldl3 and rbtree.transform_value to the rbtree module. The predicate rbtree.remove/3 has been deprecated.
• We've add some new predicates and functions to int.m. int.fold_up/4, int.fold_down/4, int.fold_up/5, int.fold_down/5, int.fold_up2/7 and int.fold_down2/7 support iteration over contiguous integer ranges.
• The predicate int.to_float/2 has now been deprecated.
• We've added a new library module, `array2d', for two-dimensional arrays.
• We've added a new module, cord, for sequences with O(1) consing and concatenation. A cord is essentially a tree structure with data stored in the leaf nodes. Joining two cords together to construct a new cord is therefore an O(1) operation.
• The dir module now handles Microsoft Windows pathnames correctly.
• dir__split_name and dir__basename are now semidet, not det. dir__split_name fails for root directories or pathnames not containing a directory separator. dir__basename fails for root directories.
• We've added some new predicates and functions to the dir module:
  • basename_det/1,
  • expand_braces/1,
  • is_directory_separator/1,
  • make_directory/4,
  • make_single_directory/4,
  • foldl2/6,
  • parent_directory/0,
  • path_name_is_absolute/1,
  • path_name_is_root_directory/1,
  • recursive_foldl2/7.
• We've added several new predicates to the io module:
  • have_symlinks/0,
  • make_symlink/4,
  • follow_symlink/4,
  • check_file_accessibility/5,
  • file_type/4,
  • input_stream_foldl2_io_maybe_stop/{6,7},
  • binary_input_stream_foldl2_io_maybe_stop/{6,7}.
• We've added several new predicates and functions to the bimap module:
  • det_insert,
  • forward_search,
  • reverse_search,
  • from_corresponding_lists,
  • map_keys,
  • map_values,
  • det_insert_from_assoc_list,
  • det_insert_from_corresponding_lists,
  • set_from_assoc_list,
  • set_from_corresponding_lists,
  • delete_key,
  • delete_value,
  • delete_keys,
  • delete_values,
  • overlay,
  • apply_forward_map_to_list,
  • apply_reverse_map_to_list,
  • foldl
• We've added predicates relation__lookup_key_set_from/3 and relation__lookup_key_set_to/3.
• The type of the arguments giving the initial set of visited nodes to relation__dfs and relation__dfsrev has changed from set_bbbtree to sparse_bitset.
• Efficiency of the operations in the relation module has been greatly improved.
• Some predicates and functions have been added to the sparse_bitset module:
  • to_set/1,
  • from_set/1,
  • member/2,
  • foldl/4,
  • foldr/4.
• exception.m now contains a predicate finally/6 which can be used to ensure that resources are released whether a called closure exits normally or throws an exception.
• exception.m now contains a predicate throw_if_near_stack_limits which can be used to prevent an application running out of stack space.
• We've changed the interface of exception.try_all/2 to separate exceptional results from normal results.
• We've added predicates multi_map.to_flat_assoc_list/2 and multi_map.from_flat_assoc_list/2.
• Several new functions have been added to the string module, namely elem/2, unsafe_elem/2, chomp/1, lstrip/1, lstrip/2, rstrip/1, rstrip/2, strip/1, prefix_length/2, suffix_length/2, string/1, string/2, string/4 and string.det_to_float/1.
• We've added some new predicates, list__map2_foldl, list__map_foldl3, and list__foldl4 to list.m.
• We've added a predicate, list__cons/3 to list.m. This is sometimes useful with higher-order code. It can also be useful with state variables. We've also added a function version.
• We've added some new predicates, map__common_subset, map__foldl3, map__overlay_large_map and map__transform_value, to map.m.
• We've added a predicate, map_fold, to set.m.
• We've added a function, pred_to_bool, to bool.m.
• We've added the three predicates, `is_nan/1', `is_inf/1' and `is_nan_or_inf/1' to float.m. These predicates are for use only on systems which support IEEE floating point arithmetic.
• We've added a function version of `hash_table__search/3'.
• We've added a predicate, copy_mutvar, to store.m.
• We've added a function, clk_tck, to time.m.
• builtin.m now contains types and insts `unify' and `compare' for use in defining user-defined equality and comparison predicates.
• builtin.m now defines insts `new' and `old' as synonyms for `free' and `any', respectively, since some of the HAL literature uses this terminology. Likewise it defines modes `no' for `new >> old' and `oo' for `old >> old'.
• We've fixed some problems with the use of `cc_nondet'.

  The incorrect cc_nondet modes of the following predicates have been removed:

  • deconstruct.arg/4
  • deconstruct.named_arg/4
  • deconstruct.limited_deconstruct/6
  • std_util.arg_cc/3
  • std_util.argument_cc/3
  • std_util.named_argument_cc/3
  • std_util.limited_deconstruct_cc/5
  These have been replaced by cc_multi versions in which success or failure is indicated by returning a maybe type.
• We've added functions get_equivalent_elements, get_minimum_element and remove_equivalent_elements to eqvclass.m.
• We've added semidet functions max_key and min_key to return the maximum and minimum keys in maps and 2-3-4 trees.
• We've added predicates member, remove_leq, remove_gt, foldl and filter to sparse_bitset.m.
• builtin.m now contains types and insts `unify' and `compare' for use in defining user-defined equality and comparison predicates.
• The following predicates, which were added in 0.11.0, have been deprecated:
  • io.current_input_stream/3
  • io.current_output_stream/3
  • io.current_binary_input_stream/3
  • io.current_binary_output_stream/3
  They were identical to the following long-existing predicates with similar names:
  • io.input_stream/3
  • io.output_stream/3
  • io.binary_input_stream/3
  • io.binary_output_stream/3
• The following functions have been added to the integer module:
  • integer.zero/0
  • integer.one/0
  • integer.det_from_string/1
  • integer.pow/2

  The predicate integer.pow/3 has been deprecated.

• We've added some functions, rational.int/1, rational.from_integer/1, rational.from_integers/2 and rational.reciprocal/1 to rational.m The function rational.rational_from_integers/2 has been deprecated.
• A new module `term_to_xml' has been added to the standard library. This module contains predicates to write arbitrary Mercury terms to an output stream as XML. Automatic generation of DTDs for Mercury types is also supported. Once a Mercury term is in XML it can be converted to many other formats such as HTML or XUL using an appropriate stylesheet.

Changes to the Mercury compiler:

• We have added optional support for a new type-accurate garbage collector as an alternative to using the Boehm et al conservative collector.

  The new collector is enabled by `--grade hlc.agc'. For details about how it works, see the paper "Accurate garbage collection in an uncooperative environment" which is available via our web page.

  Note that the new collector is a very naive copying collector, and still has a number of serious limitations which may make it undesirable for most applications. It only works with `--high-level-code'. The heap size is fixed at program startup; the collector does not attempt to resize the heap. It does not do cheap heap reclamation on backtracking. There is no support for passing terms on the Mercury heap to C code. In most cases, the Boehm et all conservative collector will perform better.

• There's a new warning option `--warn-dead-procs' which can be used for detecting unreachable code.

  This is not yet enabled by default, because it can cause some spurious warnings in modules containing code which mixes Mercury clauses and `pragma foreign_proc' declarations for the same procedure.

• `mmc --make' now works correctly with Microsoft Visual C++.
• It's now easier to use shared libraries on Linux/x86 systems with `mmc --make'. See the documentation for the `--mercury-linkage' and `--linkage' options and the `MERCURY_LINKAGE' Mmake variable in the Mercury User's Guide.
• The behaviour of the `--pre-link-command' and `--extra-init-command' options has changed. They now take a command which will be passed the names of all source files in the program or library, with the name of the main module's source file passed first. See the "Build system options" section of the "Invocation" chapter of the Mercury User's Guide for details.
• It is now possible to reconfigure an existing Mercury installation to use a different C compiler. See the "C compilers" chapter of the Mercury User's Guide for details.
• Inlining of builtins can now be disabled using the `--no-inline-builtins' option. This is done by default when debugging, as without this option the execution of builtins is not traced.
• The Mercury compiler now uses `.' and not `:' as the module separator in all output.
• The environment variables which were previously used to override the location of the standard library (MERCURY_ALL_C_INCL_DIRS, MERCURY_ALL_MC_C_INCL_DIRS, MERCURY_INT_DIR, MERCURY_C_LIB_DIR, MERCURY_MOD_LIB_MODS, MERCURY_TRACE_LIB_MODS) have been removed.
• There is a new analysis: `--analyse-exceptions'. This identifies predicates that will not throw an exception. This information is made available to the optimizing passes of the compiler.

Portability improvements:

• We have made the implementation compatible with gcc 3.4.
• Shared libraries now work on Mac OS X.

Changes to the Mercury debugger:

• Users can now limit the output from stack traces.

  The mdb command `stack' now takes an optional integer argument that specifies the maximum number of stack frames to be printed.

• Users can now put breakpoints on unify and compare predicates.

  The syntax for procedure specifications now has provision for specifying unify and compare predicates.

• Users can now save runtime values to files.

  We've added a new mdb command, `save_to_file', that saves a specified term to a specified file.

• The declarative debugger can now be told to trust entire modules or individual predicates or functions using the `trust' mdb command.
• The declarative debugger can now also tell you where a value appearing in an atom came from (i.e. the call which constructed the value).
• The declarative debugger also now supports a divide-and-query search mode. You can tell the declarative debugger to use this search mode by invoking it with the command `dd -s divide_and_query'.
• The "pretty" and "raw_pretty" print formats have had their names swapped, so the "pretty" format is now prettier than the "raw_pretty" format.

• Improvements to the .NET CLR back-end.

  We've fixed a lot of bugs, and implemented a lot more of the Mercury standard library. We have been able to bootstrap the compiler in grade `il', and also pass more than 90% of the applicable tests in the Mercury test suite. See README.DotNet for details.

• Improvements to the Java back-end.

  We've fixed a lot of bugs, and implemented a lot more of the Mercury standard library. See README.Java for details.