NEWS since Mercury 22.01
========================

Changes that may break compatibility
------------------------------------

* The predicates `read_term/3`, `read_term/4`, `read_term_with_op_table/4`,
  `read_term_with_op_table/5` have been removed from the `term_io` module
  of the Mercury standard library.

* The order of two arguments in the predicates `write_variable/4`,
  `write_variable/5`, `write_variable_with_op_table/4`, and
  `write_variable_with_op_table/5` in the `term_io` module
  has been swapped.

* The `io` module is being reorganized. Some predicates have been marked
  as obsolete, while other predicates that had been marked as obsolete
  before the release of Mercury 22.01 have been removed.

* The old random number generator in the `random` module has been removed.

* The system of operator priorities in the `ops` module has been inverted.
  Previously, given two operators of different priorities, the one that
  bound more tightly was the one with the lower numerical priority.
  Now, operators with higher numerical priorities bind more tightly.
  There are other changes as well, such as priorities no longer being
  interchangeable with other integers, some types and function symbols
  being renamed, and an updated `op_table` type class with a somewhat
  different list of methods.

  The old contents of the `ops` module is still available as
  `extras/old_library_modules/old_ops`.

* The `mercury_term_parser` module now expects the operator table to be
  specified using the updated `op_table` type class in the new `ops` module.

  The old contents of the `mercury_term_parser` module is still available as
  `extras/old_library_modules/old_mercury_term_parser`.

* The `enum/1` typeclass has been modified by having its `from_int` method
  changed from a semidet function of arity one (plus the return value)
  to a semidet predicate of arity two.

* The `sparse_bitset`, `fat_sparse_bitset` and `tree_bitset` modules
  now require the items in those sets to be instances of the `uenum` typeclass,
  not the `enum` typeclass.

* The `digraph_key` type in the `digraph` module is now an instance of
  the `uenum` typeclass, not the `enum` typeclass.

* Six predicates in the `injection` module, `det_insert/4`, `det_set/4`,
  `det_update/4`, `insert/4`, `set/4` and `update/4`, have had the order
  of their arguments changed.

* Two predicates in the `bt_array` module, `resize/4` and `shrink/4`,
  have had the order of their arguments changed.

* One predicate in the `ranges` module, `nondet_member/2`, has had the order of
  its arguments changed.

* The character sequences `<<u` and `>>u` are now recognized as single tokens.
  (They are the names of new versions of the left and right shift operators
  that expect the shift amount to be specified by an unsigned integer;
  previously, shift amounts were always specified by signed integers.)
  This means that existing code in which a `<<` or `>>` operator was followed
  immediately, without an intervening space, by a `u` character, will now
  be parsed differently.

* The compiler no longer accepts `:` as the module name separator in backquoted
  operators. (Mercury switched to using `.` as the module name separator
  around 2003.)

* The compiler now ignores comments when warning about unused arguments
  in `foreign_proc` pragmas. Warnings can no longer be suppressed by
  mentioning a variable in a comment; use a leading underscore to mark
  intentionally unused variables. This change also prevents spurious
  warnings about `return` statements caused by the word `return`
  appearing only in comments.

* We have dropped support for the x86 (32-bit) version of Cygwin.

* We have dropped support for versions of MSVC before version 19.3
  (Visual Studio 2022).

* The `--use-subdirs` and `--use-grade-subdirs` options now cause `.mh` files
  to be placed in a `Mercury/mhs` subdirectory instead of the current
  directory. This reduces clutter in the current directory, but may require
  additional options to be passed to the C compiler in order for it to find
  those header files.

* We have changed the meaning of `mmc --make name.cs`.

  The `mmc --make` target `name.cs` now means "build the .cs file
  of the named module". To build all the .c files of a program, which was
  the previous meaning of that target, use the target `program.all_cs`.

* Some (undocumented) mmake variables in compiler-generated `.dv` files
  have been renamed:

        program.cs          -> program.all_cs
        program.os          -> program.all_os
        program.pic_os      -> program.all_pic_os
        program.javas       -> program.all_javas
        program.css         -> program.all_css

        program.all_mhs     -> program.mhs_to_clean
        program.all_mihs    -> program.mihs_to_clean
        program.all_int0s   -> program.int3s_to_clean

* We have replaced the `--no-warn-only-one-format-string-error` compiler
  option with the new option named `--warn-all-format-string-errors`.

* We have disabled support for concurrency in non-parallel low-level C grades.
  It was never useful for anything other than trivial programs.

* The `clock_t` type in the `time` module of the Mercury standard library is
  now abstract, with an underlying representation of `int64` rather than `int`.
  This avoids overflow on backends where Mercury's `int` type is 32 bits.
  Code that performs arithmetic on `clock_t` values directly will need to use
  the new `clock_t_to_int64/1` access function.

Changes to the Mercury standard library
---------------------------------------

### Changes to the `array` module

* The following predicates and functions have been added:

    - pred `semidet_least_index/2`
    - pred `semidet_greatest_index/2`
    - func `uinit/2`
    - pred `uinit/3`
    - func `ugenerate/3`
    - pred `ugenerate_foldl/5`
    - pred `ugenerate_foldl2/7`
    - func `ulookup/2`
    - pred `ulookup/3`
    - pred `semidet_ulookup/3`
    - pred `unsafe_ulookup/3`
    - func `uelem/2`
    - func `unsafe_uelem/2`
    - func `uset/3`
    - pred `uset/4`
    - pred `semidet_uset/4`
    - pred `unsafe_uset/4`
    - func `uelem :=/3`
    - func `unsafe_uelem :=/3`
    - pred `uswap/4`
    - pred `unsafe_uswap/4`
    - func `umin/1`
    - pred `umin/2`
    - func `umax/1`
    - pred `umax/2`
    - pred `ubounds/3`
    - func `usize/1`
    - pred `usize/2`
    - pred `in_ubounds/2`
    - func `uresize/3`
    - pred `uresize/4`
    - func `ushrink/2`
    - pred `ushrink/3`
    - pred `fill_urange/5`

* The following predicates have been removed:

    - pred `random_permutation/4`
      (replacement: `random.shuffle_array/4` or `random.shuffle_array/5`)

    - pred `sort_fix_2014/0`
      (no replacement needed)

* The following function has been marked obsolete:

    - func `array_to_doc/1` (replacement: `pretty_printer.array_to_doc/1`)

### Changes to the `bag` module

* The following predicates and functions have been added:

    - func `ucount/1`
    - func `ucount_unique/1`
    - func `ucount_value/2`
    - pred `ucount_value/3`

### Changes to the `benchmarking` module

* The following predicates have been added:

    - pred `full_memory_stats_are_available/0`
    - pred `report_stats/3`
    - pred `report_stats/4`
    - pred `report_standard_stats/2`
    - pred `report_standard_stats/3`
    - pred `report_full_memory_stats/2`
    - pred `report_full_memory_stats/3`
    - pred `report_tabling_statistics/2`
    - pred `report_tabling_statistics/3`

* The following predicates have been marked obsolete:

    - pred `report_stats/0`
    - pred `report_full_memory_stats/0`

### Changes to the `bitmap` module

* The following predicates have been added:

    - pred `num_bytes/2`
    - pred `from_string/2`
    - pred `read_bitmap/6`
    - pred `read_bitmap/7`
    - pred `read_bitmap_range/8`
    - pred `read_bitmap_range/9`
    - pred `write_bitmap/3`
    - pred `write_bitmap/4`
    - pred `write_bitmap_range/5`
    - pred `write_bitmap_range/6`

### Changes to the `bt_array` module

* The following predicates have had the order of their arguments changed:

    - pred `resize/4`
    - pred `shrink/4`

### Changes to the `builtin` module

* The following obsolete predicate and function have been removed:

    - func `promise_only_solution/1`
    - pred `promise_only_solution_io/4`

### Changes to the `calendar` module

* The `date/0` type, whose values contain information about times
  as well as dates, has been renamed to `date_time/0`. `date_time/0`
  has previously been an equivalence type that expanded to the old
  `date/0` type.

  `date/0` is now an equivalence type that expands to `date_time/0`
  (effectively reversing their relationship). However, this is a temporary
  measure, to allow time for programmers to switch to using `date_time/0`.
  The reason for this is that at the next release, we intend to reuse the
  `date/0` name for a new type that contains only date information,
  without any time information. To encourage this switchover, the following
  predicates and functions have been marked obsolete:

    - pred `init_date/8`            (replacement: `init_date_time/8`)
    - func `det_init_date/7`        (replacement: `det_init_date_time/7`)
    - pred `unpack_date/8`          (replacement: `unpack_date_time/8`)
    - pred `date_from_string/2`     (replacement: `date_time_from_string/2`) 
    - func `det_date_from_string/1` (replacement: `det_date_time_from_string/1`)
    - func `date_to_string/1`       (replacement: `date_time_to_string/1`)

* `date_time/0` and `duration/0` values now only allow for a single positive
  leap second for any given minute.

* The following functions have been marked obsolete:

    - func `duration/2`             (replacement: `duration_between/2`)
    - func `day_duration/2`         (replacement: `fixed_duration_between/2`)

* The following functions and predicates have been added:

    - pred `init_date_time/8`
    - func `det_init_date_time/7`
    - pred `unpack_date_time/8`
    - pred `date_time_from_string/2`
    - func `det_date_time_from_string/1`
    - func `date_time_to_string/1`
    - func `days_in_month/2` 
    - pred `is_leap_year/1`
    - func `duration_between/2`
    - func `fixed_duration_between/2`

### Changes to the `char` module

* The following type has had its typeclass memberships changed:

    - The type `character` is now an instance of the new `uenum` typeclass.

* The following predicate and functions have been added:

    - func `to_uint/1`
    - pred `from_uint/2`
    - func `det_from_uint/1`

* The following function has been marked obsolete:

    - func `char_to_doc/1`   (replacement: `pretty_printer.char_to_doc/1`)

### Changes to the `construct` module

* The following predicates have been added:

    - pred `num_functors/2`
    - pred `get_functor_ordinal/3`
    - pred `get_functor_lex/3`
    - pred `construct/4`

### Changes to the `cord` module

* The following predicates and functions have been added:

    - pred `is_non_empty/1`
    - pred `foldr2/6`
    - pred `foldr3/8`
    - pred `head/2`
    - pred `is_singleton/2`
    - pred `cons_list/2`
    - pred `snoc_list/2`
    - func `ulength/1`

### Changes to the `counter` module

* The following type has been added:

    - type `ucounter/0`

* The following predicate and function have been added:

    - func `uinit/1`
    - pred `uinit/2`
    - pred `uallocate/1`

### Changes to the `diet` module

* The following functions and predicates have been added:

    - func `from_sorted_list/1`
    - pred `nondet_member/2`
    - func `ucount/1`

* The following obsolete predicate has been removed:

    - pred `empty/1`

### Changes to the `digraph` module

* The following type has had its typeclass memberships changed:

    - The `digraph_key(T)` type is now an instance of the `uenum` typeclass,
      and is no longer an instance of the `enum` typeclass.

* The following predicates and functions have been added:

    - func `symmetric_closure/1`            (synonym for `sc/1`)
    - func `transitive_closure/1`           (synonym for `tc/1`)
    - func `reflexive_transitive_closure/1` (synonym for `rtc/1`)
    - pred `reachable_vertices_from/3`

* We have improved the implementations of transitive closure and reflexive
  transitive closure.

### New `edit_distance` module

* This new module defines operations that, when given a query sequence
  and a set of candidate sequences, finds out which candidate sequence
  is closest to the query sequence, in terms of the configurable `distances`
  added by operations such as inserting or replacing elements in sequences.

### Changes to the `edit_seq` module

* This module deals with many integers, including row numbers, column numbers,
  and operation costs, that cannot be negative. To ensure that this restriction
  is enforced automatically, we have changed the types of all these integers
  from `int` to `uint`.

### Changes to the `enum` module

* The following typeclass has been modified:

    - The `enum/1` typeclass has had its `from_int` method changed from a
      semidet function of arity one (plus the return value) to a semidet
      predicate of arity two.

* The following typeclass has been added:

    - typeclass `uenum/1`

* The following functions have been added:

    - func `from_int/1`                 (replaces class method; born obsolete)
    - func `det_from_uint/1`

### Changes to the `fat_sparse_bitset` module

* The following type has had its typeclass memberships changed:

    - The `fat_sparse_bitset(T)` type now requires `T` to be an instance of the
     `uenum` typeclass, replacing the earlier requirement that it be
     a member of the `enum` typeclass.

* The documentation of the following predicates and functions have been
  clarified:

    - func `sorted_list_to_set/1`
    - pred `sorted_list_to_set/2`

* The following functions and predicates have been added:

    - func `from_list/1`
    - func `from_sorted_list/1`
    - func `ucount/1`
    - pred `nondet_member/1`

* The following obsolete predicate has been removed:

    - pred `empty/1`

### New `fatter_sparse_bitset` module

* This new module defines a more compact version of the data structure
  defined by the `fat_sparse_bitset` module, and implements the same set of
  operations on this data structure.

### Changes to the `float` module

* The following function has been marked obsolete:

    - func `float_to_doc/1`     (replacement: `pretty_printer.float_to_doc/1`)

### Changes to the `getopt` module

* The following predicates have been added:

    - pred `recognize_options/8`
    - pred `recognize_all_options/8`

* The following predicate has been marked obsolete:

    - pred `record_arguments/8` (replacement: `getopt.recognize_options/8`)

### Changes to the `hash_table` module

* The following predicate has been added:

    - pred `lookup/3`

* The following obsolete predicates have been removed:

    - pred `char_hash/2`
    - pred `float_hash/2`
    - pred `generic_hash/2`
    - pred `int_hash/2`
    - pred `string_hash/2`
    - pred `uint_hash/2`

### Changes to the `injection` module

* The following predicates have had the order of their arguments changed:

    - pred `det_insert/4`
    - pred `det_set/4`
    - pred `det_update/4`
    - pred `insert/4`
    - pred `set/4`
    - pred `update/4`

### Changes to the `int` module

* The following type has had its typeclass memberships changed:

    - The type `int` is now an instance of the new `uenum` typeclass.

* The following predicates and functions have been added:

    - func `<<u/2`
    - func `>>u/2`
    - func `clamp/3`
    - func `unchecked_left_ushift/2`
    - func `unchecked_right_ushift/2`
    - func `ubits_per_int/0`
    - pred `ubits_per_int/1`

* The following function has been marked obsolete:

    - func `int_to_doc/1`    (replacement: `pretty_printer.int_to_doc/1`)

### Changes to the `int8` module

* The following functions have been added:

    - func `<<u/2`
    - func `>>u/2`
    - func `clamp/3`
    - func `unchecked_left_ushift/2`
    - func `unchecked_right_ushift/2`

* The following function has been marked obsolete:

    - func `int8_to_doc/1`   (replacement: `pretty_printer.int8_to_doc/1`)

### Changes to the `int16` module

* The following functions have been added:

    - func `<<u/2`
    - func `>>u/2`
    - func `clamp/3`
    - func `unchecked_left_ushift/2`
    - func `unchecked_right_ushift/2`

* The following function has been marked obsolete:

    - func `int16_to_doc/1`  (replacement: `pretty_printer.int16_to_doc/1`)

### Changes to the `int32` module

* The following predicates and functions have been added:

    - func `<<u/2`
    - func `>>u/2`
    - func `clamp/3`
    - pred `det_from_int64/2`
    - func `from_int64/1`
    - func `unchecked_left_ushift/2`
    - func `unchecked_right_ushift/2`

* The following function has been marked obsolete:

    - func `int32_to_doc/1`  (replacement: `pretty_printer.int32_to_doc/1`)

### Changes to the `int64` module

* The following functions have been added:

    - func `<<u/2`
    - func `>>u/2`
    - func `clamp/3`
    - func `unchecked_left_ushift/2`
    - func `unchecked_right_ushift/2`

* The following function has been marked obsolete:

    - func `int64_to_doc/1`  (replacement: `pretty_printer.int64_to_doc/1`)

### Changes to the `io` module

* The following predicates and functions have been added:

    - pred `make_io_error_from_system_error/5`
    - pred `make_io_error_from_windows_error/5`
    - pred `get_errno_error/2`
    - pred `get_exception_object_error/2`
    - pred `get_system_error/2`
    - pred `get_system_error_name/2`
    - pred `get_windows_error/2`
    - func `init_posn/0`
    - pred `read_file_as_string_wf/3`
    - pred `read_file_as_string_wf/4`
    - pred `read_file_as_string_and_num_code_units_wf/3`
    - pred `read_file_as_string_and_num_code_units_wf/4`
    - pred `read_named_file_as_string_wf/4`
    - pred `read_named_file_as_lines_wf/4`
    - pred `system_error_is_success/1`
    - pred `write_binary_string_utf8/3`
    - pred `write_binary_string_utf8/4`
    - pred `write_prefixed_lines/4`
    - pred `write_prefixed_lines/5`

* The following obsolete predicates have been removed:

    - pred `see/3`                  (replacement: `prolog.see/3`)
    - pred `see_binary/3`           (replacement: `prolog.see_binary/3`)
    - pred `seen/2`                 (replacement: `prolog.seen/2`)
    - pred `seen_binary/2`          (replacement: `prolog.seen_binary/2`)
    - pred `tell/4`                 (replacement: `prolog.tell/4`)
    - pred `tell_binary/4`          (replacement: `prolog.tell_binary/4`)
    - pred `told/2`                 (replacement: `prolog.told/2`)
    - pred `told_binary/2`          (replacement: `prolog.told_binary/2`)

* The following predicates have been marked obsolete:

    - pred `read_bitmap/6`          (replacement: `bitmap.read_bitmap/6`)
    - pred `read_bitmap/7`          (replacement: `bitmap.read_bitmap/7`)
    - pred `read_bitmap/8`          (replacement: `bitmap.read_bitmap_range/8`)
    - pred `read_bitmap/9`          (replacement: `bitmap.read_bitmap_range/9`)
    - pred `write_bitmap/3`         (replacement: `bitmap.write_bitmap/3`)
    - pred `write_bitmap/4`         (replacement: `bitmap.write_bitmap/4`)
    - pred `write_bitmap/5`         (replacement: `bitmap.write_bitmap_range/5`)
    - pred `write_bitmap/6`         (replacement: `bitmap.write_bitmap_range/6`)

    - pred `report_stats/3`
            (replacement: `benchmarking.report_stats/3`)
    - pred `report_stats/4`
            (replacement: `benchmarking.report_stats/4`)
    - pred `report_standard_stats/2`
            (replacement: `benchmarking.report_standard_stats/2`)
    - pred `report_standard_stats/3`
            (replacement: `benchmarking.report_standard_stats/3`)
    - pred `report_full_memory_stats/2`
            (replacement: `benchmarking.report_full_memory_stats/2`)
    - pred `report_full_memory_stats/3`
            (replacement: `benchmarking.report_full_memory_stats/3`)
    - pred `report_tabling_statistics/2`
            (replacement: `benchmarking.report_tabling_statistics/2`)
    - pred `report_tabling_statistics/3`
            (replacement: `benchmarking.report_tabling_statistics/3`)

    - pred `remove_file/4`
            (replacement: `io.file.remove_file/4`)
    - pred `remove_file_recursively/4`
            (replacement: `io.file.remove_file_recursively/4`)
    - pred `rename_file/5`
            (replacement: `io.file.rename_file/5`)
    - pred `have_symlinks/0`
            (replacement: `io.file.have_symlinks/0`)
    - pred `make_symlink/5`
            (replacement: `io.file.make_symlink/5`)
    - pred `read_symlink/4`
            (replacement: `io.file.read_symlink/4`)
    - pred `check_file_accessibility/5`
            (replacement: `io.file.check_file_accessibility/5`)
    - pred `file_type/5`
            (replacement: `io.file.file_type/5`)
    - pred `file_modification_time/4`
            (replacement: `io.file.file_modification_time/4`)
    - pred `make_temp_file/3`
            (replacement: `io.file.make_temp_file/3`)
    - pred `make_temp_file/6`
            (replacement: `io.file.make_temp_file/6`)
    - pred `make_temp_directory/3`
            (replacement: `io.file.make_temp_directory/3`)
    - pred `make_temp_directory/6`
            (replacement: `io.file.make_temp_directory/6`)
    - pred `have_make_temp_directory/0`
            (replacement: `io.file.have_make_temp_directory/0`)
    - pred `get_temp_directory/3`
            (replacement: `io.file.get_temp_directory/3`)

    - pred `get_environment_var/4`
            (replacement: `io.environment.get_environment_var/4`)
    - pred `set_environment_var/5`
            (replacement: `io.environment.set_environment_var/5`)
    - pred `set_environment_var/4`
            (replacement: `io.environment.set_environment_var/4`)
    - pred `have_set_environment_var/0`
            (replacement: `io.environment.have_set_environment_var/0`)
    - pred `get_environment_var_map/3`
            (replacement: `io.environment.get_environment_var_map/3`)

    - pred `call_system/4`
            (replacement: `io.call_system.call_system/4`)
    - pred `call_system_return_signal/4`
            (replacement: `io.call_system.call_system_return_signal/4`)

    - pred `get_globals/3`          (replacement: a user-defined mutable)
    - pred `set_globals/3`          (replacement: a user-defined mutable)
    - pred `update_globals/3`       (replacement: a user-defined mutable)

    - pred `input_stream_foldl/5`
           (replacement: `stream.input_stream_fold/6`)
    - pred `input_stream_fold/6`
           (replacement: `stream.input_stream_fold/6`)
    - pred `input_stream_foldl_io/4`
           (replacement: `stream.input_stream_fold_state/5`)
    - pred `input_stream_foldl_io/5`
           (replacement: `stream.input_stream_fold_state/5`)
    - pred `input_stream_foldl2_io/5`
           (replacement: `stream.input_stream_foldl_state/6`)
    - pred `input_stream_foldl2_io/6`
           (replacement: `stream.input_stream_fold_state/6`)
    - pred `input_stream_foldl2_io_maybe_stop/5`
           (replacement: `stream.input_stream_fold2_state_maybe_stop/6`)
    - pred `binary_input_stream_foldl/5`
           (replacement: `stream.input_stream_fold/6`)
    - pred `binary_input_stream_foldl/6`
           (replacement: `stream.input_stream_fold/6`)
    - pred `binary_input_stream_foldl_io/4`
           (replacement: `stream.input_stream_fold_state/5`)
    - pred `binary_input_stream_foldl2_io/5`
           (replacement: `stream.input_stream_fold2_state/6`)
    - pred `binary_input_stream_foldl2_io/6`
           (replacement: `stream.input_stream_fold2_state/6`)
    - pred `binary_input_stream_foldl2_io_maybe_stop/5`
           (replacement: `stream.input_stream_fold2_state_maybe_stop/6`)
    - pred `binary_input_stream_foldl2_io_maybe_stop/6`
           (replacement: `stream.input_stream_fold2_state_maybe_stop/6`)

### New `io.call_system` module

* This new module has these predicates and functions:

    - pred `call_system/4`
    - pred `call_system_return_signal/4`
    - func `decode_system_command_exit_code/1`

### New `io.environment` module

* This new module has these predicates:

    - pred `get_environment_var/4`
    - pred `set_environment_var/5`
    - pred `set_environment_var/4`
    - pred `have_set_environment_var/0`
    - pred `get_environment_var_map/3`

### New `io.file` module

* This new module has these predicates:

    - pred `remove_file/4`
    - pred `remove_file_recursively/4`
    - pred `rename_file/5`
    - pred `have_symlinks/0`
    - pred `make_symlink/5`
    - pred `read_symlink/4`
    - pred `check_file_accessibility/5`
    - pred `file_type/5`
    - pred `file_modification_time/4`
    - pred `make_temp_file/3`
    - pred `make_temp_file/6`
    - pred `make_temp_directory/3`
    - pred `make_temp_directory/6`
    - pred `have_make_temp_directory/0`
    - pred `get_temp_directory/3`

### Changes to the `library` module

* The following functions have been added:

    - func `architecture/0`
    - func `mercury_version/0`
    - func `package_version/0`

### Changes to the `list` module

* The following predicates and functions have been added:

    - pred `chunk_foldl/5`
    - pred `chunk_foldl2/7`
    - pred `chunk_foldl3/9`
    - pred `chunk_foldl4/11`
    - pred `gap_foldl/5`
    - pred `head/2`
    - pred `tail/2`
    - pred `det_head/2`
    - pred `det_tail/2`
    - func `inst_preserving_condense/1`
    - func `intersect/2`
    - pred `intersect/3`
    - func `intersect_lists/1`
    - pred `intersect_lists/2`
    - pred `intersperse/3`
    - pred `intersperse_list/3`
    - pred `intersperse_list_last/4`
    - pred `is_non_empty/1`
    - pred `is_singleton/2`
    - pred `last_gap_foldl/6`
    - func `map_corresponding4/5`
    - pred `map_corresponding4/6`
    - func `merge_lists/1`
    - func `merge_lists/2`
    - pred `merge_lists/2`
    - pred `merge_lists/3`
    - func `merge_lists_and_remove_dups/1`
    - func `merge_lists_and_remove_dups/2`
    - pred `merge_lists_and_remove_dups/2`
    - pred `merge_lists_and_remove_dups/3`
    - pred `nondet_member/2`
    - pred `remove_prefix/3`
    - func `take_while_not/2`
    - pred `take_while_not/3`
    - pred `take_while_not/4`
    - func `ulength/1`
    - pred `ulength/2`

* The following function has been marked obsolete:

    - func `list_to_doc/1`  (replacement: `pretty_printer.list_to_doc/1`)

### Changes to the `map` module

* The following predicates and functions have been added:

    - pred `is_non_empty/1`
    - pred `max_key/2`
    - pred `min_key/2`
    - pred `compose_maps/3`
    - pred `sorted_keys_match/2`
    - func `ucount/1`
    - pred `ucount/2`

* We have added `cc_multi` versions of many of the higher-order predicates in
  this module.

### Changes to the `mercury_term_lexer` module

* The representation type of the tokens returned has been tightened.
  Previously, the documented type of tokens contained two function symbols
  that were needed only by the implementation of the lexer, and could
  never be returned in the generated token lists. The new definition
  differs from the old one only in the fact that it omits these two
  function symbols.

### Changes to the `multi_map` module

* The following predicates and functions have been added:

    - func `all_ucount/1`
    - pred `all_ucount/2`
    - func `get_values_for_key/2`
    - func `ucount/1`
    - pred `ucount/2`

### Changes to the `one_or_more` module

* The following predicates and functions have been added:

    - pred `is_non_empty/1`
    - pred `nondet_member/2`
    - func `ulength/1`
    - pred `ulength/2`

* The following function has been marked obsolete:

    - func `one_or_more_to_doc/1`
                        (replacement: `pretty_printer.one_or_more_to_doc/1`)

### Changes to the `one_or_more_map` module

* The following predicates and functions have been added:

    - func `all_ucount/1`
    - pred `all_ucount/2`
    - func `get_values_for_key/2`
    - func `reverse_add/3`
    - pred `reverse_add/4`
    - func `ucount/1`
    - pred `ucount/2`

### Changes to the `ops` module

* The representation of operator priorities has been changed. Priorities
  used to be represented as signed integers between 0 and 1200, with
  higher numbers representing operators that bind less tightly.
  Priorities are now represented using unsigned integers between 0u and 1500u,
  with higher numbers representing operators that bind more tightly.
  To guard against priorities being unintentionally confused with
  other kinds of numbers, they are now wrapped in the `prio` function symbol.

* The representation of the set of operators that a string may represent
  has been changed. Operator tables used to map each operator string
  (such as "-") to a list of operator descriptions, each of which could be
  infix, binary prefix, prefix or postfix. This allowed a table entry
  to declare an operator string to be e.g. an infix operator using
  two separate entries, with different priorities. Operator tables now map
  each operator string to a structure which has

  - one slot for a description of an infix operator,
  - one slot for a description of a binary prefix operator,
  - one slot for a description of a unary prefix operator, and
  - one slot for a description of a unary postfix operator.

  Besides making some nonsensical entries that could exist in old op tables
  unrepresentable, the new op table also allows users of operator information
  to test more simply and quickly whether an operator string represents
  e.g. a prefix operator.

* The `assoc` type has been renamed to `arg_prio_gt_or_ge`, which
  reflects its semantics. Its function symbols `x` and `y` have been
  renamed to `arg_gt` and `arg_ge` respectively.

* The list of methods in the `op_table` type class has been changed.

 - The method `max_priority/1` has been replaced by the method
   `loosest_op_priority/1`.

 - The method `lookup_op/2` has been renamed to `is_op/2`.

 - The new method `universal_priority/1` has been added. It is intended to
   replace uses of `max_priority + 1` to denote a context that accept terms
   using any operator, regardless of its priority.

 - The new method `tightest_op_priority/1` has been added. It is intended to
   replace uses of the integer constant `0` as a priority.

 - The new method `comma_priority/1` has been added. It is intended to denote
   the priority of the comma character, which separates term arguments,
   when used as an operator.

 - The argument types of the `lookup_op_infos/2` method have been changed.

* The following predicates and functions have been added:

    - func `decrement_priority/1`
    - func `increment_priority/1`
    - func `mercury_op_table_arg_priority/0`
    - func `mercury_op_table_comma_priority/0`
    - func `mercury_op_table_loosest_op_priority/0`
    - func `mercury_op_table_tightest_op_priority/0`
    - func `mercury_op_table_universal_priority/0`
    - pred `mercury_op_table_binary_prefix_op/5`
    - pred `mercury_op_table_infix_op/5`
    - pred `mercury_op_table_lookup_operator_term/3`
    - pred `mercury_op_table_postfix_op/4`
    - pred `mercury_op_table_prefix_op/4`
    - pred `mercury_op_table_search_binary_prefix_op/4`
    - pred `mercury_op_table_search_infix_op/4`
    - pred `mercury_op_table_search_op/1`
    - pred `mercury_op_table_search_op_infos/3`
    - pred `mercury_op_table_search_postfix_op/3`
    - pred `mercury_op_table_search_prefix_op/3`
    - func `min_priority_for_arg/2`
    - pred `priority_ge/2`
    - pred `priority_gt/2`
    - pred `priority_le/2`
    - pred `priority_lt/2`

* The following predicates have been renamed:

    - pred `mercury_op_table_prefix_op/5` to    `op_infos_prefix_op/5`
    - pred `mercury_op_table_binary_prefix_op/5` to
                                                `op_infos_binary_prefix_op/5`
    - pred `mercury_op_table_infix_op/5` to     `op_infos_infix_op/5`
    - pred `mercury_op_table_postfix_op/5` to   `op_infos_postfix_op/5`

### Changes to the `pqueue` module

* The following predicate has been added:

    - pred `map_values/3`

### Changes to the `pretty_printer` module

* The following predicates and functions have been added:

    - func `array_to_doc/1`
    - func `char_to_doc/1`
    - func `float_to_doc/1`
    - func `get_formatter_map_entry_types/1`
    - func `int_to_doc/1`
    - func `int8_to_doc/1`
    - func `int16_to_doc/1`
    - func `int32_to_doc/1`
    - func `int64_to_doc/1`
    - func `list_to_doc/1`
    - func `one_or_more_to_doc/1`
    - func `string_to_doc/1`
    - func `tree234_to_doc/1`
    - func `uint_to_doc/1`
    - func `uint8_to_doc/1`
    - func `uint16_to_doc/1`
    - func `uint32_to_doc/1`
    - func `uint64_to_doc/1`
    - func `version_array_to_doc/1`
    - pred `write_doc_formatted/3`
    - pred `write_doc_formatted/4`

### Changes to the `prolog` module

* The following predicate has been deleted:

    - pred `is/2`

### New `ra_list` module

* This new module contains operations on random access lists.

### Changes to the `random` module

* The old random number generator has been removed. It has been replaced by the
  new type class random number generation framework defined in this module.
  As a result, the following predicates have been removed:

    - pred `init/2`
    - pred `random/3`
    - pred `random/5`
    - pred `randmax/3`
    - pred `randcount/3`
    - pred `permutation/4`
            (replacement: `random.shuffle_list/4` or `random.shuffle_list/5`)

### Changes to the `ranges` module

* The following predicate has had the order of its arguments changed:

    - pred `nondet_member/2`

* The following predicates and functions have been added:

    - func `make_singleton_set/1`
    - pred `is_singleton/2`
    - pred `contains/2`
    - func `count/1`
    - pred `delete/3`
    - pred `delete_list/3`
    - pred `difference/3`
    - func `intersect/2`
    - pred `intersect/3`
    - pred `insert_list/3`
    - func `list_to_ranges/1`
    - pred `list_to_ranges/2`
    - pred `nondet_range_member/3`
    - pred `restrict_min/3`
    - pred `restrict_max/3`
    - pred `restrict_range/4`
    - pred `search_range/4`
    - func `set_to_ranges/1`
    - pred `set_to_ranges/2`
    - func `ucount/1`
    - pred `union/3`

* The following function and predicate have been marked obsolete:

    - func `intersection/2` (replacement: `intersect/2`)
    - pred `range_member/3` (replacement: `nondet_range_member`/3)

### Changes to the `rbtree` module

* The following predicates and functions have been added:

    - func `foldr/3`
    - pred `foldr/4`
    - pred `foldr2/6`
    - pred `foldr_values/4`
    - func `ucount/1`
    - pred `ucount/2`

### Changes to the `set` module

* The following predicates and functions have been added:

    - pred `map2_fold/6`
    - pred `nondet_member/2`
    - func `ucount/1`
    - pred `ucount/2`

* The following obsolete predicates and function have been removed:

    - pred `empty/1`
    - pred `non_empty/1`
    - func `set/1`

### Changes to the `set_bbbtree` module

* The following predicates and functions have been added:

    - pred `nondet_member/2`
    - func `ucount/1`
    - pred `ucount/2`

* The following obsolete predicates have been removed:

    - pred `empty/1`
    - pred `non_empty/1`
    - pred `nondet_member/2`

### Changes to the `set_ctree234` module

* The following predicates and functions have been added:

    - func `from_sorted_list/1`
    - pred `nondet_member/2`
    - pred `power_intersect/2`
    - func `ucount/1`

* The following predicate has been marked obsolete:

    - pred `one_member/2` (replacement: `nondet_member/2`)

* The following obsolete predicates have been removed:

    - pred `empty/1`
    - pred `non_empty/1`

### Changes to the `set_ordlist` module

* The following predicates and functions have been added:

    - pred `nondet_member/2`
    - func `ucount/1`
    - pred `ucount/2`

* The following obsolete predicates have been removed:

    - pred `empty/1`
    - pred `non_empty/1`

### Changes to the `set_tree234` module

* The following predicates and functions have been added:

    - func `from_sorted_list/1`
    - pred `nondet_member/2`
    - func `ucount/1`

* The following obsolete predicates have been removed:

    - pred `empty/1`
    - pred `non_empty/1`

### Changes to the `set_unordlist` module

* We have changed the behaviour of the `(out, in) is nondet` mode of the
  predicate `member/2` so that it does not return any element of the set more
  than once.

* The following predicates and functions have been added:

    - pred `nondet_member/2`
    - func `ucount/1`
    - pred `ucount/2`

* The following obsolete predicates have been removed:

    - pred `empty/1`
    - pred `non_empty/1`

### Changes to the `sparse_bitset` module

* The following type has had its typeclass memberships changed:

    - The `sparse_bitset(T)` type now requires `T` to be an instance of the
      `uenum` typeclass, replacing the earlier requirement that it be
      a member of the `enum` typeclass.

* The following predicates and functions have been added:

    - func `from_list/1`
    - func `from_sorted_list/1`
    - pred `nondet_member/2`
    - func `ucount/1`

* The following obsolete predicate has been removed:

    - pred `empty/1`

* The documentation of the following predicates and functions have been
  clarified:

    - func `sorted_list_to_set/1`
    - pred `sorted_list_to_set/2`

### Changes to the `std_util` module

* We have changed the behaviour of `pow/3` so that it throws an exception
  if it is called with a negative integer as its second argument.

### Changes to the `string` module

* The following predicates and functions have been added:

    - func `add_prefix/2`
    - func `between_code_points/3`
    - pred `between_code_points/4`
    - pred `check_well_formedness/2`
    - pred `code_point_offset/3`
    - pred `code_point_offset/4`
    - pred `contains_match/2`
    - func `count_code_points/1`
    - pred `count_code_points/2`
    - pred `find_first_char/3`
    - pred `find_first_char_start/4`
    - pred `find_last_char/3`
    - func `internal_string_encoding/0`
    - func `left_by_code_point/2`
    - pred `left_by_code_point/3`
    - func `right_by_code_point/2`
    - pred `right_by_code_point/3`
    - pred `split_by_code_point/3`
    - pred `split_by_code_point/4`
    - pred `replace_all_sv/4`
    - pred `unsafe_find_first_char_start/4`

* The following obsolete modes have been removed from the following predicates:

    - pred `to_char_list(uo, in)`
    - pred `to_rev_char_list(in, out)`
    - pred `append(out, out, in)`
    - pred `prefix(in, out)`
    - pred `suffix(in, out)`

* The following predicates and functions have been marked obsolete:

    - func `string_to_doc/1`
                            (replacement: `pretty_printer.string_to_doc/1`)
    - func `between_codepoints/3`    (replacement: `between_code_points/3`)
    - pred `between_codepoints/4`    (replacement: `between_code_points/4`)
    - pred `codepoint_offset/3`      (replacement: `code_point_offset/3`)
    - pred `codepoint_offset/4`      (replacement: `code_point_offset/4`)
    - func `count_codepoints/1`      (replacement: `count_code_points/1`)
    - pred `count_codepoints/2`      (replacement: `count_code_points/2`)
    - func `left_by_codepoint/2`     (replacement: `left_by_code_point/2`)
    - pred `left_by_codepoint/3`     (replacement: `left_by_code_point/3`)
    - func `right_by_codepoint/2`    (replacement: `right_by_code_point/2`)
    - pred `right_by_codepoint/3`    (replacement: `right_by_code_point/3`)
    - pred `split_by_codepoint/3`    (replacement: `split_by_code_point/3`)
    - pred `split_by_codepoint/4`    (replacement: `split_by_code_point/4`)

* The semantics of the `format_table_max` function has been changed.
  Previously, the function's documentation was silent on how the returned
  string would be constructed if some columns contained strings that exceeded
  that column's maximum width. What it actually did was to split the line
  at the end of the too-long columns, continuing the row in the next line
  at the expected initial column. Since splitting the line is probably not
  what users of this function expect, we have now changed this function
  to never break a row into more than one line. We have also documented
  this behavior.

### Changes to the `string.builder` module

* The following predicates and functions have been added:

    - pred `append_char/3`
    - pred `append_string/3`
    - pred `append_strings/3`
    - pred `append_strings_sep/4`
    - pred `format/4`
    - func `total_num_code_points/1`
    - pred `total_num_code_points_is_at_most/2`

### Changes to the `term` module

* The following type has had its typeclass memberships changed:

    - The type `var/1` is now an instance of the new `uenum` typeclass.

* The following predicates have been marked obsolete:

    - pred `generic_term/1`
            (replacement: `with_type` annotations on expressions)

    - pred `decimal_term_to_int/2`
            (replacement: `term_int.decimal_term_to_int/2`)
    - pred `term_to_int/2`
            (replacement: `term_int.term_to_int/2`)
    - pred `term_to_int8/2`
            (replacement: `term_int.term_to_int8/2`)
    - pred `term_to_int16/2`
            (replacement: `term_int.term_to_int16/2`)
    - pred `term_to_int32/2`
            (replacement: `term_int.term_to_int32/2`)
    - pred `term_to_int64/2`
            (replacement: `term_int.term_to_int64/2`)
    - pred `term_to_uint/2`
            (replacement: `term_int.term_to_uint/2`)
    - pred `term_to_uint8/2`
            (replacement: `term_int.term_to_uint8/2`)
    - pred `term_to_uint16/2`
            (replacement: `term_int.term_to_uint16/2`)
    - pred `term_to_uint32/2`
            (replacement: `term_int.term_to_uint32/2`)
    - pred `term_to_uint64/2`
            (replacement: `term_int.term_to_uint64/2`)
    - func `int_to_decimal_term/2`
            (replacement: `term_int.int_to_decimal_term/2`)
    - func `int8_to_decimal_term/2`
            (replacement: `term_int.int8_to_decimal_term/2`)
    - func `int16_to_decimal_term/2`
            (replacement: `term_int.int16_to_decimal_term/2`)
    - func `int32_to_decimal_term/2`
            (replacement: `term_int.int32_to_decimal_term/2`)
    - func `int64_to_decimal_term/2`
            (replacement: `term_int.int64_to_decimal_term/2`)
    - func `uint_to_decimal_term/2`
            (replacement: `term_int.uint_to_decimal_term/2`)
    - func `uint8_to_decimal_term/2`
            (replacement: `term_int.uint8_to_decimal_term/2`)
    - func `uint16_to_decimal_term/2`
            (replacement: `term_int.uint16_to_decimal_term/2`)
    - func `uint32_to_decimal_term/2`
            (replacement: `term_int.uint32_to_decimal_term/2`)
    - func `uint64_to_decimal_term/2`
            (replacement: `term_int.uint64_to_decimal_term/2`)

    - pred `occurs/3`
            (replacement: `term_subst.var_occurs_in_subst_term/2`)
    - pred `occurs_list/3`
            (replacement: `term_subst.var_occurs_in_subst_terms/2`)
    - pred `is_ground/1`
            (replacement: `term_subst.term_is_ground/1`)
    - pred `is_ground_in_bindings/2`
            (replacement: `term_subst.term_is_ground_in_bindings/2`)
    - pred `rename_var_in_term/4`
            (replacement: `term_subst.rename_var_in_term/4`)
    - pred `rename_var_in_terms/4`
            (replacement: `term_subst.rename_var_in_terms/4`)
    - pred `apply_renaming_in_var/3`
            (replacement: `term_subst.apply_renaming_in_var/3`)
    - pred `apply_renaming_in_vars/3`
            (replacement: `term_subst.apply_renaming_in_vars/3`)
    - pred `apply_renaming_in_term/3`
            (replacement: `term_subst.apply_renaming_in_term/3`)
    - pred `apply_renaming_in_terms/3`
            (replacement: `term_subst.apply_renaming_in_terms/3`)
    - pred `substitute_var_in_term/4`
            (replacement: `term_subst.substitute_var_in_term/4`)
    - pred `substitute_var_in_terms/4`
            (replacement: `term_subst.substitute_var_in_terms/4`)
    - pred `substitute_corresponding_in_term/3`
            (replacement: `term_subst.substitute_corresponding_in_term/3`)
    - pred `substitute_corresponding_in_terms/3`
            (replacement: `term_subst.substitute_corresponding_in_terms/3`)
    - pred `apply_substitution_in_term/3`
            (replacement: `term_subst.apply_substitution_in_term/3`)
    - pred `apply_substitution_in_terms/3`
            (replacement: `term_subst.apply_substitution_in_terms/3`)
    - pred `apply_rec_substitution_in_term/3`
            (replacement: `term_subst.apply_rec_substitution_in_term/3`)
    - pred `apply_rec_substitution_in_terms/3`
            (replacement: `term_subst.apply_rec_substitution_in_terms/3`)
    - func `term_list_to_var_list/2`
            (replacement: `term_subst.term_list_to_var_list/1`)
    - pred `term_list_to_var_list/2`
            (replacement: `term_subst.term_list_to_var_list/2`)
    - func `var_list_to_term_list/2`
            (replacement: `term_subst.var_list_to_term_list/1`)
    - pred `var_list_to_term_list/2`
            (replacement: `term_subst.var_list_to_term_list/2`)

    - pred `unify_term/4`
            (replacement: `term_unify.unify_terms/4`)
    - pred `unify_term_list/4`
            (replacement: `term_unify.unify_term_lists/4`)
    - pred `unify_term_dont_bind/5`
            (replacement: `term_unify.unify_terms_dont_bind/5`)
    - pred `unify_term_list_dont_bind/5`
            (replacement: `term_unify.unify_term_lists_dont_bind/5`)
    - pred `list_subsumes/3`
            (replacement: `term_unify.first_term_list_subsumes_second/3`)

    - func `vars/1`
            (replacement: `term_vars.vars_in_term/1`)
    - pred `vars/2`
            (replacement: `term_vars.vars_in_term/2`)
    - func `vars_2/2`
            (replacement: `term_vars.vars_in_term_acc/3`)
    - pred `vars_2/3`
            (replacement: `term_vars.vars_in_term_acc/3`)
    - func `vars_list/1`
            (replacement: `term_vars.vars_in_terms/1`)
    - pred `vars_list/2`
            (replacement: `term_vars.vars_in_terms/2`)
    - pred `contains_var/2`
            (replacement: `term_vars.term_contains_var/2`)
    - pred `contains_var_list/2`
            (replacement: `term_vars.terms_contain_var/2`)

    - func `context_init/2`
            (replacement: `term_context.context_init/2`)
    - pred `context_init/3`
            (replacement: `term_context.context_init/2`)
    - func `context_init/0`
            (replacement: `term_context.dummy_context/0`)
    - pred `context_init/1`
            (replacement: `term_context.dummy_context/0`)
    - func `dummy_context_init/0`
            (replacement: `term_context.dummy_context/0`)
    - pred `is_dummy_context/1`
            (replacement: `term_context.is_dummy_context/1`)
    - func `context_file/1`
            (replacement: `term_context.context_file/1`)
    - pred `context_file/2`
            (replacement: `term_context.context_file/1`)
    - func `context_line/1`
            (replacement: `term_context.context_line/1`)
    - pred `context_line/2`
            (replacement: `term_context.context_line/1`)

### New `term_context` module

* This new module defines the `term_context` type, and contains predicates
  and functions that operate on that type.

### New `term_int` module

* This new module contains predicates that recognize terms that contain
  integers, and functions that construct such terms.

### Changes to the `term_io` module

* The following predicates and functions have been added:

    - func `constant_to_string/2`
    - func `escaped_char_to_string/2`
    - func `quoted_char_to_string/2`
    - pred `format_constant/4`
    - pred `format_escaped_char/4`
    - pred `format_escaped_string/4`
    - pred `format_quoted_atom/4`
    - pred `format_quoted_char/4`
    - pred `format_quoted_string/4`
    - pred `format_term/5`
    - pred `format_term_nl/5`
    - pred `format_term_with_op_table/6`
    - pred `format_term_nl_with_op_table/6`
    - pred `format_variable/5`
    - pred `format_variable_with_op_table/6`
    - func `term_to_string/2`
    - func `term_nl_to_string/2`
    - func `term_with_op_table_to_string/3`
    - func `term_nl_with_op_table_to_string/3`
    - func `variable_to_string/2`
    - func `variable_with_op_table_to_string/3`
    - pred `write_quoted_atom/3`
    - pred `write_quoted_atom/4`
    - pred `write_quoted_char/3`
    - pred `write_quoted_char/4`
    - pred `write_quoted_string/3`
    - pred `write_quoted_string/4`

* The order of the arguments of the following predicates has been changed:

    - pred `write_variable/4`
    - pred `write_variable/5`
    - pred `write_variable_with_op_table/4`
    - pred `write_variable_with_op_table/5`

* The following predicates have been removed:

    - pred `read_term/3`
            (replacement: `mercury_term_parser.read_term/3`)
    - pred `read_term/4`
            (replacement: `mercury_term_parser.read_term/4`)
    - pred `read_term_with_op_table/4`
            (replacement: `mercury_term_parser.read_term_with_op_table/4`)
    - pred `read_term_with_op_table/5`
            (replacement: `mercury_term_parser.read_term_with_op_table/5`)

### New `term_subst` module

* This new module contains predicates that perform substitutions
  of various kinds on terms.

### New `term_unify` module

* This new module contains predicates that perform unifications.

### New `term_vars` module

* This new module contains predicates and functions that find
  variables in terms.

### Changes to the `thread` module

* The following predicates have been added:

    - pred `spawn_native_joinable/5`
    - pred `join_thread/4`

### Changes to the `time` module

*  The `tm_sec` field of the `tm/0` type now only allows for a single positive
   leap second for any given minute.

* The `clock_t` type is now abstract (see the compatibility note above).
  The following functions have been added for accessing its representation:

    - func `clock_t_to_int/1`
    - func `clock_t_to_int64/1`

### Changes to the `tree_bitset` module

* The following predicates and functions have been added:

    - func `from_list/1`
    - func `from_sorted_list/1`
    - pred `nondet_member/2`
    - pred `remove_leq/3`
    - pred `remove_gt/3`
    - func `ucount/1`

* The documentation of the following predicates and functions have been
  clarified:

    - func `sorted_list_to_set/1`
    - pred `sorted_list_to_set/2`

### Changes to the `tree234` module

* The following predicates and functions have been added:

    - pred `is_non_empty/1`
    - pred `max_key/2`
    - pred `min_key/2`
    - pred `sorted_keys_match/2`
    - func `ucount/1`
    - pred `ucount/2`

* The following function has been marked obsolete:

    - func `tree234_to_doc/1`
                            (replacement: `pretty_printer.tree234_to_doc/1`)

* We have added `cc_multi` versions of many of the higher-order predicates in
  this module.

### Changes to the `tree_bitset` module

* The following predicates and functions have been added:

    - func `ucount/1`
    - pred `ucount/2`

* The following obsolete predicate has been removed:

    - pred `empty/1`

### Changes to the `type_desc` module

* The following predicates have been added:

    - pred `make_type/3`
    - pred `pseudo_type_ctor/2`
    - pred `pseudo_type_args/2`

### Changes to the `uint` module

* The following type has had its typeclass memberships changed:

    - The type `uint` is now an instance of the new `uenum` typeclass.

* The following functions have been added:

    - func `<<u/2`
    - func `>>u/2`
    - func `clamp/3`
    - func `unchecked_left_ushift/2`
    - func `unchecked_right_ushift/2`
    - func `ubits_per_uint/0`

* The following function has been marked obsolete:

    - func `uint_to_doc/1`   (replacement: `pretty_printer.uint_to_doc/1`)

### Changes to the `uint8` module

* The following functions have been added:

    - func `<<u/2`
    - func `>>u/2`
    - func `clamp/3`
    - func `unchecked_left_ushift/2`
    - func `unchecked_right_ushift/2`

* The following function has been marked obsolete:

    - func `uint8_to_doc/1`  (replacement: `pretty_printer.uint8_to_doc/1`)

### Changes to the `uint16` module

* The following functions have been added:

    - func `<<u/2`
    - func `>>u/2`
    - func `clamp/3`
    - func `unchecked_left_ushift/2`
    - func `unchecked_right_ushift/2`

* The following function has been marked obsolete:

    - func `uint16_to_doc/1` (replacement: `pretty_printer.uint16_to_doc/1`)

### Changes to the `uint32` module

* The following predicates and functions have been added:

    - func `<<u/2`
    - func `>>u/2`
    - func `clamp/3`
    - func `det_to_int/1`
    - pred `to_int/2`
    - func `unchecked_left_ushift/2`
    - func `unchecked_right_ushift/2`

* The following function has been marked obsolete:

    - func `uint32_to_doc/1` (replacement: `pretty_printer.uint32_to_doc/1`)

### Changes to the `uint64` module

* The following predicates and functions have been added:

    - func `<<u/2`
    - func `>>u/2`
    - func `clamp/3`
    - func `det_to_int/1`
    - pred `to_int/2`
    - func `unchecked_left_ushift/2`
    - func `unchecked_right_ushift/2`

* The following function has been marked obsolete:

    - func `uint64_to_doc/1` (replacement: `pretty_printer.uint64_to_doc`/1)

### Changes to the `version_array` module

* The following predicates and functions have been added:

    - func `uinit/2`
    - func `unsafe_uinit/2`
    - pred `lookup/3`
    - func `ulookup/2`
    - pred `ulookup/3`
    - pred `uset/4`
    - func `uelem/2`
    - func `uelem :=/3`
    - func `usize/1`
    - func `uresize/3`
    - pred `uresize/4`

* The following function has been marked obsolete:

    - func `version_array_to_doc/1`
                       (replacement: `pretty_printer.version_array_to_doc/1`)

### Changes to the `version_array2d` module

* The following predicates and functions have been added:

    - func `uinit/3`
    - pred `ubounds/3`
    - pred `in_ubounds/3`
    - pred `lookup/4`
    - func `ulookup/3`
    - pred `ulookup/4`
    - pred `uset/5`
    - func `uelem/3`
    - func `uelem :=/4`
    - func `usize/1`
    - func `uresize/4`
    - pred `uresize/5`

### Changes to the `version_bitmap` module

* The following predicates have been added:

    - pred `get_bit/3`
    - pred `set_bit/4`

### Changes to the `version_hash_table` module

* The following predicate has been added:

    - pred `lookup/3`

* The following obsolete predicates have been removed:

    - pred `char_hash/2`
    - pred `float_hash/2`
    - pred `generic_hash/2`
    - pred `int_hash/2`
    - pred `string_hash/2`
    - pred `uint_hash/2`

Changes to the Mercury language
-------------------------------

* The new pragma `format_call` can now be used to ask the compiler
  to perform the same checks on calls to a named predicate or function
  as the compiler performs on calls to `string.format`, `io.format` and
  `stream.string_writer.format`. These checks test whether the format string
  matches the provided list of values.

* You can now disable another two kinds of warning with a `disable_warning`
  scope.

  First, code such as

      disable_warning [unknown_format_calls] (
          ...
      )

  will disable warnings about any calls in the scope to `string.format`,
  `io.format` and/or `stream.string_writer.format` for which the compiler
  cannot tell whether there are any mismatches between the format string
  and the supplied values, even if the module is compiled with
  `--warn-unknown-format-calls`.

  Second, code such as

      disable_warning [warn_repeated_singleton_vars] (
          ...
      )

  will disable warnings in the scope about variables whose names start with
  an underscore, indicating that they should be singleton variables, but
  which nevertheless occur more than once.

* The new pragma `require_tail_recursion` can now be used to ask the compiler
  to warn you about recursive calls (either self-recursive or mutually
  recursive) that a named predicate or function makes that are not tail
  recursive, and whose iteration lengths are therefore limited by the
  amount of available stack space.

  The existing option `--warn-non-tail-recursion` implicitly asks the compiler
  to do this for every predicate and function in the module being compiled.
  The new pragma `disable_non_tail_recursion_reports` will disable any such
  reports about calls from the predicate or function it names.

* Floating point number literals may now contain an underscore
  between the digits forming the fraction part and the `e` or `E` that
  introduces the exponent part.

* You can now use the escape sequence `'\e'` to refer to the ESC (escape)
  character, just as you can use `'\n'` to refer to the newline character.

Changes to the Mercury compiler
-------------------------------

* We now enforce a (previously unstated) requirement that existentially
  quantified type variables and existential class constraints in a subtype
  definition are listed in the same order as in the supertype definition.

* We have fixed a bug where the compiler generated incorrect code in
  C# and Java grades when a subtype type definition did not repeat the field
  names of its base type.

* The compiler now ignores comments when warning about unused arguments
  in `foreign_proc` pragmas. Warnings can no longer be suppressed by
  mentioning a variable in a comment; use a leading underscore to mark
  intentionally unused variables. This change also prevents spurious
  warnings about `return` statements caused by the word `return`
  appearing only in comments.

* We have improved the typechecking and modechecking of type conversion
  expressions.

* We have fixed a bug where `--warn-unused-imports` did not warn about
  unused modules that are also imported by an ancestor of the current module.

* The compiler now uses colors in error messages to draw programmers' attention
  to the most relevant parts of diagnostics. Users can change the color scheme
  using the new option `--color-scheme` or using the new environment variable
  `MERCURY_COLOR_SCHEME`. They can also disable the use of color entirely
  using the new option `--no-color-diagnostics` or by setting the `NO_COLOR`
  environment variable. For the details, please see the new `Diagnostic output`
  chapter of the Mercury Users' guide.

* We have added a new option `--warn-ambiguous-pragmas`
  that tells the compiler to generate warnings for pragmas that specify
  a name/arity pair, when there is both a predicate and a function
  with that name and arity, and the pragma does not specify which one
  it is for.

* We have added a new option `--warn-redundant-coerce`,
  that tells the compiler to generate warnings for type conversions
  from one type to the same type. This option is enabled by default.

* We have added a new option `--warn-unused-types`,
  that tells the compiler to generate warnings for type definitions
  that are visible only in their defining module, but are not used
  in that module.

* We have added a new option `--warn-repeated-singleton-variables`,
  which may be shortened to `--warn-repeated-singleton-vars`,
  that tells the compiler to generate warnings for variables whose name
  starts with an underscore, indicating that they should be singletons,
  that nevertheless occur more than once. Until now, warnings about
  such variables were controlled by the  `--warn-singleton-variables` option.
  This option is enabled by default.

* We have added the option `--error-files-in-subdir` to place `.err` files
  under the `Mercury` subdirectory when using `mmc --make`.

* We have raised the default value of `--output-compile-error-lines` to 100.

* We have added a new option `--reverse-error-order` that tells the compiler
  to output error messages for higher line numbers before error messages
  for lower line numbers.

* We have added a new option `--show-local-call-tree`
  that tells the compiler to output a representation of the call tree
  of the predicates and functions of the module as ordered by a depth-first
  left-to-right traversal of the bodies of the first (i.e. main) procedures
  of those predicates and functions. This can suggest a good order
  for the positions of those predicates and functions in the source code.

* We have added a new option `--show-pred-movability`. If a user specifies
  this option one or more times, each time with the name of a predicate or
  function as the option's argument, then the compiler will generate a report
  about the effect of moving the named predicates and/or functions to a new
  module. This report will list all the other predicates and/or functions
  that should be moved with them, and will warn about any unwanted coupling
  the move would create between the old module and the new.

* We have added a new option `--warn-can-fail-function`. If the user specifies
  this option, the compiler will generate a warning for every function
  whose primary mode (which means the mode in which all its arguments
  are input) can fail without generating a return value.

  This option is for people who prefer that all functions be total,
  and that functions that compute a value only in some circumstances
  (i.e. partial functions) be expressed as predicates instead.

* We have added a new option `--warn-unsorted-import-blocks`. If the user
  specifies this option, the compiler will generate a warning if any line
  contains `import_module` or `use_module` declarations for more than one
  module, or if a block of such declarations on consecutive lines
  are not sorted on module name.

  The discipline enforced by this option can standardize the appearance
  of the sections of Mercury modules containing these declarations, make
  diffs of changes to these sections easier to read, and spare programmers
  from having to decide on a case-by-case basis exactly where they want
  to add a new `import_module` or `use_module` declaration.

* We have added two new options, `--warn-unneeded-initial-statevars`,
  and `--warn-unneeded-initial-statevars-lambda`, which report, for
  clause heads and lambda expressions respectively, when an argument
  of the form !.SV in their argument list is never updated. In most cases,
  changing such arguments into non-statevars will improve the code
  by avoiding giving readers of the code a false expectation of an update.
  (An exception is when a !.SV argument is not updated in one clause,
  but is updated in another clause.) Both options are on by default.

* We have added two new options, `--warn-unneeded-final-statevars`,
  and `--warn-unneeded-final-statevars-lambda`, which report, for
  clause heads and lambda expressions respectively, when an argument
  of the form !:SV in their argument list is guaranteed to be unified
  with the !.SV argument in the same argument list. In the absence of
  constraints that require keeping the predicate signature unchanged
  (e.g. to allow the predicate to be passed to a higher order construct),
  the !:SV argument should be deleted, and if the only use of the !.SV
  argument was to set the value of the !:SV argument, then the !.SV
  argument should be deleted too. Both options are on by default.

* We have made `--warn-non-contiguous-clauses` the default.

* We have added a new option, `--allow-non-contiguity-for`, which modifies
  the operation of two existing options, `--warn-non-contiguous-clauses` and
  `--warn-non-contiguous-foreign-procs`. If either of those two options
  is specified, the compiler will normally generate a warning if there is
  a gap in the list of clauses for a given predicate. The new option allows
  programmers to relax this requirement selectively. An option such as
  `--allow-non-contiguity-for p1,f2,p3` tells the compiler to allow
  the clauses of the named predicates and/or functions to be intermingled
  with each other, but not with the clauses of any other predicates
  or functions. This option may be given more than once.

* We have added a new option, `--warn-too-private-instances`, which
  asks the compiler to generate warnings for instances that are private
  to the module containing them, even though both the typeclass they are for
  and all the type constructors occurring in their argument vector
  are visible outside that module.

* We have replaced the `--no-warn-only-one-format-string-error` compiler option
  with the new option named `--warn-all-format-string-errors`.

* We have renamed the `--generate-module-order` compiler option
  to `--also-output-module-order`, and changed the extension of the file
  to which it writes its output: it is now `.module_order`.

* The deprecated option `--trail-segments` has been deleted, and the grade
  component `trseg` is no longer accepted as a synonym for `tr`.

* The new options `--java-runtime-flags` and `--quoted-java-runtime-flag`
  can be used to set flags for the Java interpreter in the launcher shell
  scripts or batch files generated by the compiler when creating executables
  in the `java` grade.

* `--javac-flags` is now accepted as a synonym for `--java-flags`. Also,
  `--javac-flag` is now accepted as a synonym for `--java-flag`.

* We have changed the preferred name of several options that each specify
  a flag to be passed to a command after quoting. The new names are
  the following:

      --quoted-cflag              (old name: --cflag)    
      --quoted-gcc-flag           (old name: --gcc-flag)    
      --quoted-clang-flag         (old name: --clang-flag)    
      --quoted-msvc-flag          (old name: --msvc-flag)    
      --quoted-javac-flag         (old name: --javac-flag)    
      --quoted-java-flag          (old name: --java-flag)    
      --quoted-java-runtime-flag  (old name: --java-runtime-flag)    
      --quoted-csharp-flag        (old name: --csharp-flag)    
      --quoted-ld-flag            (old name: --ld-flag)    
      --quoted-ld-libflag         (old name: --ld-libflag)    

  The compiler still accepts the old names, but we intend to remove them
  after the next stable release.

* We have changed the preferred name of the `--warn-interface-imports option`
  to `--warn-unused-interface-imports`, which is more descriptive.

  The compiler still accepts the old name, but we intend to remove it
  after the next stable release.

* On macOS systems, the configure script now uses the value of the
  `MACOSX_DEPLOYMENT_TARGET` environment variable as the default value for the
  deployment target, if set.

* The `--no-ansi-c` option has been deprecated and will be removed in a future
  release. The option has not had any effect for a long time.

* We have deleted the `--java-object-file-extension` option, which has
  only ever had one useful value, which is the default value, ".class".

* We have deleted the `--generate-bytecode` option, which has never been
  useful, because the bytecode interpreter it generated code for was never
  complete enough to be usable.

* The `--install-command-dir-option` option has been deprecated and will be
  removed in a future release. This option has not had any effect for a long
  time.

* We have added more options to selectively turn off warnings that were
  previously not under such control. These options are the following.

      --no-warn-cannot-table
      --no-warn-disj-fills-partial-inst
      --no-warn-duplicate-abstract-instances
      --no-warn-exported-insts-for-private-type
      --no-warn-missing-descendant-modules
      --no-warn-missing-state-var-init
      --no-warn-moved-trace-goal
      --no-warn-no-auto-parallelisation
      --no-warn-no-recursion
      --no-warn-nonexported-pragma
      --no-warn-requested-by-code
      --no-warn-requested-by-option
      --no-warn-subtype-ctor-order
      --no-warn-typecheck-ambiguity-limit
      --no-warn-unknown-warning-name
      --no-warn-unneeded-purity-indicator
      --no-warn-unneeded-purity-pragma
      --no-warn-unneeded-purity-pred-decl

* We have renamed three existing options:

      --inform-ite-instead-of-switch       to --warn-ite-instead-of-switch
      --inform-incomplete-switch           to --warn-incomplete-switch
      --inform-incomplete-switch-threshold to --warn-incomplete-switch-threshold

  These options will still be available under their old names at least until
  the next release.

* We have added the new option `--no-warn-redundant-code`, which tells
  the compiler not to generate warnings about redundant elements in
  Mercury code, such as duplicate imports of the same module. These warnings
  were previously controlled by the `--no-warn-simple-code` option.

Changes to the Mercury debugger
-------------------------------

* The `dump` command has a new option: `dump -p Var` will dump the value
  of the given variable in a prettyprinted form.

* The `dump` command can now also dump only the selected part
  of a given variable.

* The `stack` command now identifies cliques by drawing boxes next to them
  on the left hand side of the screen.

Changes to the Mercury deep profiler
------------------------------------

* Programs that have been compiled in a deep profiling grade will now,
  by default, put profiling data in files whose names contain both the name
  of the program being profiled, and the date and time of the profiling run.
  The file names will have the form `<prog>_on_<date>_at_<time>.data` and
  `<prog>_on_<date>_at_<time>.procrep`.

  To get the old behaviour, pass the runtime option `--deep-std-name` via the
  `MERCURY_OPTIONS` environment variable. This will put the profiling data
  in files named `Deep.data` and `Deep.procrep`.

Changes to the Mercury implementation
-------------------------------------

* We have upgraded the bundled Boehm GC to v8.2.8 and libatomic_ops to v7.8.2.

Portability improvements
------------------------

* We now support using the 64-bit (x64) and ARM64 versions of Microsoft Visual
  C++ as a C compiler with Mercury, including building Mercury installations
  targeting Windows on ARM64.
  See [README.MS-VisualC.md](Documentation/README.MS-VisualC.md) for further
  details.

* We have updated the script `tools/configure_cross` to support
  cross-compiling using clang.

Changes to the extras distribution
----------------------------------

* We have deleted the `old_term_parser` library.

Other changes
-------------

* We have added a new option, `--with-pkgversion`, to the configure script.
  This option lets you specify an identifying string that will be included in
  the version information displayed by programs in the Mercury system.


For news about earlier versions, see the Documentation/NEWS_* files.
