NEWS for Mercury 22.01

Changes that may break compatibility

• We have removed is as a synonym for unification.

• We have reserved =</2 as a type name.

• A term with a top-level functor coerce/1 is now treated as a type conversion expression. To call a function named coerce/1, you can module qualify the name at the call site, or wrap parentheses around the name, e.g. (coerce)(Arg).

• We have renamed the lexer and parser modules of the Mercury standard library to mercury_term_lexer and mercury_term_parser respectively.

• We have made slight changes to the names and/or the functionality of several predicates in the getopt and getopt_io modules.

• We have removed the legacy support for the Alpha architecture.

• We have dropped support for macOS 10.8 and earlier.

• We have removed the Erlang backend as it was unmaintained.

Changes to the Mercury standard library

New module: random.system_rng

• This module provides an interface to a platform specific cryptographically secure random number generator that is seeded from the OS entropy pool.

Changes to the array module

• The following obsolete predicates and functions have been removed:

  • func bsearch/3 (replacement: binary_search/3)
  • pred bsearch/4 (replacement: binary_search/4)
  • func least_index/1 (replacement: min/1)
  • func greatest_index/1 (replacement: max/1)

• The following predicate has been added:

  • pred generate_foldl2/7

Changes to the array2d module

• The following predicates and functions have been added:

  • func lookup/3 (synonym for Array ^ elem(R, C))
  • pred lookup/4 (synonym for Array ^ elem(R, C))
  • func unsafe_lookup/3 (synonym for Array ^ unsafe_elem(R, C))
  • pred unsafe_lookup/4 (synonym for Array ^ unsafe_elem(R, C))

• The lists/1 function now returns an empty list for a 0x0 array.

Changes to the assoc_list module

• The following predicates and functions have been added:

  • func common_subset/2
  • pred maybe_from_corresponding_lists/3

Changes to the bag module

• The following obsolete predicates and functions have been removed:

  • func to_set_without_duplicates/1 (replacement: func to_set/1)
  • pred to_set_without_duplicates/2 (replacement: func to_set/1)

Changes to the bitmap module

• The following predicates and functions have been added:

  • func get_bit/2
  • func get_bits/2
  • func get_byte/2
  • pred set_bit/4
  • pred set_bits/4
  • pred set_byte/4
  • func unsafe_get_bit/2
  • func unsafe_get_bits/2
  • func unsafe_get_byte/2
  • pred unsafe_set_bit/4
  • pred unsafe_set_bits/4
  • pred unsafe_set_byte/4

Changes to the char module

• The following predicates have been added:

  • pred unsafe_base_digit_to_int/3
  • pred to_utf8_uint8/2
  • pred to_utf16_uint16/2

• The following obsolete predicates and functions have been removed:

  • func det_int_to_digit/1 (replacement: det_int_to_decimal_digit/1)
  • pred det_int_to_digit/2 (replacement: det_int_to_decimal_digit/2)
  • pred digit_to_int/2 (replacement: decimal_digit_to_int/2)
  • pred int_to_digit/2 (replacement: int_to_decimal_digit/2)

Changes to the cord module

• The following predicates have been added:

  • pred foldl2/6
  • pred foldl3/8

Changes to the dir module

• The following predicate has been added:

  • pred general_foldl2/8

Changes to the getopt module

• The following new predicates have been added:

  • pred record_arguments/8
  • pred expand_file_specials/8

• The following variants of the existing process_options predicate have been added:

  • pred process_options_io/6
  • pred process_options_io/7
  • pred process_options_track_io/9
  • pred process_options_userdata/8
  • pred process_options_userdata_io/10

  The ones whose names have an _io suffix do the same jobs as the corresponding predicates without the _io suffix, with the exception that they also have a pair of I/O state arguments that allow them to implement file_special options. This functionality used to be available only from the getopt_io module.

• The following predicates have had their argument types changed:

  • pred process_options/6
  • pred process_options/7
  • pred process_options_track/7

  All these predicates used to return error indications in the form of a simple string. They now return error indications using the existing structured type option_error, which can be converted into a string on demand.

• The following predicates have been deleted:

  • pred process_options_se/6
  • pred process_options_se/7
  • pred process_options_track_se/7

  Their functionality is now available from the predicates with the same name minus the _se suffix.

Changes to the getopt_io module

• This module has been deprecated. For now, it exports the same functionality as the updated getopt module, but it is scheduled to be deleted after the next release.

Changes to the int module

• The following functions have been added:

  • func uint_to_lc_hex_string/2 (synonym for uint_to_hex_string/2)
  • func uint64_to_lc_hex_string/2 (synonym for uint64_to_hex_string/2)

• The following obsolete predicates and functions have been removed:

  • pred is/2 (replacement: =, i.e. unification)
  • func legacy_left_shift/2 (replacement: <<)
  • func legacy_right_shift/2 (replacement: >>)

Changes to the int32 module

• The following functions have been added:

  • func cast_to_int8
  • func cast_from_int8
  • func cast_to_int16
  • func cast_from_int16
  • func cast_to_int64
  • func cast_from_int64

Changes to the integer module

• The following obsolete functions have been removed:

  • func from_base_string/2 (replacement: pred from_base_string/3)
  • func from_string/2 (replacement: pred from_string/2)
  • func int/2 (replacement: det_to_int/1)

Changes to the io module

• The following predicates have been added to this module:

  • pred get_environment_var_map/3
  • pred read_binary_int8_unboxed/5
  • pred read_binary_uint8_unboxed/5
  • pred read_named_file_as_string/4
  • pred read_named_file_as_lines/4
  • pred write_line_cc/4

• The following obsolete predicates have been removed:

  • pred make_temp/3 (replacement: make_temp_file/3)
  • pred make_temp/5 (replacement: make_temp_file/5)

• The following predicates have been marked as obsolete:

  • pred see/4 (replacement: prolog.see/4)
  • pred see_binary/4 (replacement: prolog.see_binary/4)
  • 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 predicate has been renamed:

  • pred report_stats/2 to report_standard_stats/2.

Changes to the lexer module

• This module has been renamed to mercury_term_lexer, to make name clashes between it and user-written modules less likely.

Changes to the list module

• The following predicates have been added:

  • pred delete_nth/3
  • pred foldl7/16
  • pred foldl8/18
  • pred foldl4_corresponding/11

• The following obsolete predicate has been removed:

  • pred takewhile/4 (replacement: take_while/4)

Changes to the map module

• The following predicates have been added to this module:

  • pred foldl6/14
  • pred foldl6_values/14
  • pred foldr6/14

Changes to the maybe module

• The following predicates have been added to this module:

  • pred foldl3_maybe/8
  • pred foldl4_maybe/10
  • pred foldl5_maybe/12
  • pred map_foldl4_maybe/11
  • pred map_foldl5_maybe/13

Changes to the parser module

• This module has been renamed to mercury_term_parser, to make name clashes between it and user-written modules less likely.

Changes to the prolog module

• The following predicate has been added to this module:

  • pred is/2 (moved here from the int module)
  • pred see/4 (moved here from the io module)
  • pred see_binary/4 (moved here from the io module)
  • pred seen/2 (moved here from the io module)
  • pred seen_binary/2 (moved here from the io module)
  • pred tell/4 (moved here from the io module)
  • pred tell_binary/4 (moved here from the io module)
  • pred told/2 (moved here from the io module)
  • pred told_binary/2 (moved here from the io module)

Changes to the random module

• The following obsolete predicate has been removed:

  • pred test/4 (replacement: none)

Changes to the std_util module

• The following obsolete predicates and functions have been removed:

  • func maybe_func/2 (replacement: func maybe.func_to_maybe/1)
  • pred maybe_pred/3 (replacement: func maybe.pred_to_maybe/1)

Changes to the string module

• The following functions have been added:

  • func add_suffix/2
  • func split_into_lines/1
  • pred to_uint/2
  • func det_to_uint/1
  • pred base_string_to_uint/3
  • func det_base_string_to_uint/2
  • func uint_to_hex_string/1
  • func uint_to_uc_hex_string/1
  • func uint_to_octal_string/1
  • func uint64_to_hex_string/1
  • func uint64_to_uc_hex_string/1
  • func uint64_to_octal_string/1

• The following function symbols have been added to the type poly_type:

  • i8(int8)
  • i16(int16)
  • i32(int32)
  • i64(int64)
  • u8(uint8)
  • u16(uint16)
  • u32(uint32)
  • u64(uint64)

  This allows predicates such as string.format and io.format to operate on values of not just the word sized integer types int and uint, but on sized versions of them as well.

Changes to the term module

• The following obsolete predicates and functions have been removed:

  • func var_id/1 (replacement: var_to_int/1)

  • func relabel_variable/3 (replacement: rename_var_in_term/4)
  • pred relabel_variable/4 (replacement: rename_var_in_term/4)
  • func relabel_variables/3 (replacement: rename_var_in_terms/4)

  • pred relabel_variables/4 (replacement: rename_var_in_terms/4)

  • func rename/3 (replacement: rename_var_in_term/4)
  • pred rename/4 (replacement: rename_var_in_term/4)
  • func rename_list/3 (replacement: rename_var_in_terms/4)

  • pred rename_list/4 (replacement: rename_var_in_terms/4)

  • func apply_renaming/3 (replacement: apply_renaming_in_term/3)
  • pred apply_renaming/3 (replacement: apply_renaming_in_term/3)
  • func apply_renaming_to_list/3 (replacement: apply_renaming_in_terms/3)

  • pred apply_renaming_to_list/3 (replacement: apply_renaming_in_terms/3)

  • func apply_variable_renaming/2 (replacement: apply_renaming_in_term/3)
  • pred apply_variable_renaming/3 (replacement: apply_renaming_in_term/3)
  • func apply_variable_renaming_to_list/2 (replacement: apply_renaming_in_terms/3)

  • pred apply_variable_renaming_to_list/3 (replacement: apply_renaming_in_terms/3)

  • func apply_variable_renaming_to_var/2 (replacement: apply_renaming_in_var/3)
  • pred apply_variable_renaming_to_var/3 (replacement: apply_renaming_in_var/3)
  • func apply_variable_renaming_to_vars/2 (replacement: apply_renaming_in_vars/3)

  • pred apply_variable_renaming_to_vars/3 (replacement: apply_renaming_in_vars/3)

  • func substitute/3 (replacement: substitute_var_in_term/4)
  • pred substitute/4 (replacement: substitute_var_in_term/4)
  • func substitute_list/3 (replacement: substitute_var_in_terms/4)

  • pred substitute_list/4 (replacement: substitute_var_in_terms/4)

  • func substitute_corresponding/3 (replacement: substitute_corresponding_in_term/4)
  • pred substitute_corresponding/4 (replacement: substitute_corresponding_in_term/4)
  • func substitute_corresponding_list/3 (replacement: substitute_corresponding_in_terms/4)

  • pred substitute_corresponding_list/4 (replacement: substitute_corresponding_in_terms/4)

  • func apply_substitution/2 (replacement: apply_substitution_in_term/3)
  • pred apply_substitution/3 (replacement: apply_substitution_in_term/3)
  • func apply_substitution_to_list/2 (replacement: apply_substitution_in_terms/3)

  • pred apply_substitution_to_list/3 (replacement: apply_substitution_in_terms/3)

  • func apply_rec_substitution/2 (replacement: apply_rec_substitution_in_term/3)
  • pred apply_rec_substitution/3 (replacement: apply_rec_substitution_in_term/3)
  • func apply_rec_substitution_to_list/2 (replacement: apply_rec_substitution_in_terms/3)

  • pred apply_rec_substitution_to_list/3 (replacement: apply_rec_substitution_in_terms/3)

Changes to the thread module

• The following predicate and functions have been added:

  • func init_thread_options/0
  • pred set_min_stack_size/3
  • pred spawn_native/5

Changes to the thread.mvar module

• The following obsolete function has been removed:

  • func init/1 (replacement: impure_init/1)

Changes to the thread.semaphore module

• The following obsolete function has been removed:

  • func init/1 (replacement: impure_init/1)

Changes to the time module

• The following obsolete functions have been removed:

  • func ctime/1 (replacement: localtime/4 and asctime/1)
  • func localtime/1 (replacement: localtime/4)
  • func mktime/1 (replacement: mktime/4)

Changes to the tree234 module

• The following predicates have been added to this module:

  • pred foldl6/14
  • pred foldl6_values/14
  • pred foldr6/14

Changes to the uint16 module

• The following functions have been added:

  • pred from_uint/2
  • func det_from_uint/1
  • func cast_from_uint/1
  • func rotate_left/2
  • func rotate_right/2
  • func unchecked_rotate_left/2
  • func unchecked_rotate_right/2
  • func set_bit/2
  • func unchecked_set_bit/2
  • func clear_bit/2
  • func unchecked_clear_bit/2
  • func flip_bit/2
  • func unchecked_flip_bit/2
  • func bit_is_set/2
  • func unchecked_bit_is_set/2
  • func bit_is_clear/2
  • func unchecked_bit_is_clear/2
  • func cast_from_uint8/1
  • func cast_to_uint8/1

Changes to the uint32 module

• The following functions have been added:

  • pred from_uint/2
  • func det_from_uint/1
  • func rotate_left/2
  • func rotate_right/2
  • func unchecked_rotate_left/2
  • func unchecked_rotate_right/2
  • func set_bit/2
  • func unchecked_set_bit/2
  • func clear_bit/2
  • func unchecked_clear_bit/2
  • func flip_bit/2
  • func unchecked_flip_bit/2
  • func bit_is_set/2
  • func unchecked_bit_is_set/2
  • func bit_is_clear/2
  • func unchecked_bit_is_clear/2
  • func cast_from_uint8/1
  • func cast_to_uint8/1
  • func cast_from_uint16/1
  • func cast_to_uint16/1

Changes to the uint64 module

• The following functions have been added:

  • func cast_from_uint/1
  • func rotate_left/2
  • func rotate_right/2
  • func unchecked_rotate_left/2
  • func unchecked_rotate_right/2
  • func set_bit/2
  • func unchecked_set_bit/2
  • func clear_bit/2
  • func unchecked_clear_bit/2
  • func flip_bit/2
  • func unchecked_flip_bit/2
  • func bit_is_set/2
  • func unchecked_bit_is_set/2
  • func bit_is_clear/2
  • func unchecked_bit_is_clear/2
  • func cast_from_uint8/1
  • func cast_to_uint8/1

Changes to the uint8 module

• The following functions have been added:

  • pred from_uint/2
  • func det_from_uint/1
  • func cast_from_uint/1
  • func rotate_left/2
  • func rotate_right/2
  • func unchecked_rotate_left/2
  • func unchecked_rotate_right/2
  • func set_bit/2
  • func unchecked_set_bit/2
  • func clear_bit/2
  • func unchecked_clear_bit/2
  • func flip_bit/2
  • func unchecked_flip_bit/2
  • func bit_is_set/2
  • func unchecked_bit_is_set/2
  • func bit_is_clear/2
  • func unchecked_bit_is_clear/2

Changes to the varset module

• The following obsolete predicates have been removed:

  • pred merge_subst/4 (replacement: merge_renaming/4)
  • pred merge_subst_without_names/4 (replacement: merge_renaming_without_names/4)

• The following functions and predicates have been added:

  • func unname_var/2
  • pred unname_var/3
  • pred undo_default_names/2

Changes to the Mercury language

• The type system now supports subtypes, which work in tandem with type conversion expressions (“coerce”). For example, the following defines a subtype real_color of a discriminated union type color:

    :- type color
        --->    rgb(float, float, float)
        ;       cmyk(float, float, float, float)
        ;       named(string).
  
    :- type real_color =< color
        --->    rgb(float, float, float)
        ;       cmyk(float, float, float, float).

  A term of type real_color can be converted to a term of type color with coerce(Term). A term of type color can be converted to a term of type real_color if it has an appropriate inst. Subtypes share a common data representation with their base types, so the type conversions do not cost anything at runtime.

• Field names no longer need to be unique within a module.

• The compiler can implement tabling only when generating C code. When compiling a predicate that has a pragma memo specified for it in a non-C grade, it necessarily ignores the pragma, but normally it prints a warning about this fact. The compiler now supports a new attribute, disable_warning_if_ignored, that suppresses such warnings for a pragma memo if included in the pragma’s attribute list, like this:

    :- pragma memo(predname/arity, [disable_warning_if_ignored])]).

• A pragma foreign_proc declaration can now include an attribute may_not_export_body that prevents its body (i.e. the foreign code) from being duplicated outside of the target file for that module by intermodule optimization. This is useful when the foreign code refers to types, functions, etc. that should be kept local to the target file of that module. Unlike the may_not_duplicate attribute, may_not_export_body does not prevent inlining of the foreign procedure into other procedures in the same module.

• Many pragmas contain a name/arity pair for specifying the predicate or function they apply to; an example is

    :- pragma inline(init/1).

  If the module in which this pragma occurs contains both a function init/1 and a predicate init/1, then this pragma is ambiguous. Traditionally, the Mercury compiler applied such ambiguous pragma to both the function and the predicate. The programmers who wished the pragma to apply to only one of them had to rename the other.

  Now, pragmas that take a name/arity pair can specify whether they are intended to apply to a function or to a predicate by putting a func() or pred() wrapper around the name/arity pair, like this:

    :- pragma inline(func(init/1)).     % applies ONLY to func init/1.
    :- pragma inline(pred(init/1)).     % applies ONLY to pred init/1.

  This new syntax applies to all of the following kinds of pragmas:

    check_termination
    consider_used
    does_not_terminate
    fact_table
    inline
    loop_check
    memo
    minimal_model
    mode_check_clauses
    no_determinism_warning
    no_inline
    obsolete
    promise_equivalent_clauses
    promise_pure
    promise_semipure
    require_tail_recursion
    terminates
    type_spec

Changes to the Mercury compiler

• If a command line first enables an optimization (say opt1), and then sets the optimization level to N with -O<N>, then the compiler will now keep opt1 enabled even if opt1 is not normally enabled at optimization level N.

• Due to a bug fix, the --warn-unused-imports option is now stricter in warning about modules that are imported in the interface section but are not used in the interface section.

• We have fixed parsing of reverse implication goals (A <= B).

• By default, the compiler now checks some aspects of a module semantics when generating the .int and .int2 interface files for that module. (For example, it generates error messages for references to undefined types, insts and modes.) This new behavior can be switched off for now with the new option --no-halt-at-invalid-interface. This new option replaces the old --no-print-errors-warnings-when-generating-interface option, but once any problems caused by the new approach have been ironed out, we intend to delete the --halt-at-invalid-interface option as well.

• In an earlier release, we extended the syntax of :- inst declarations to allow programmers to specify which type constructor’s values the inst is meant for. At that time, these functioned only as documentation, but the compiler now reports error messages for situations in which an inst that was declared to be intended for values of one type constructor is applied to values of another type constructor.

• The new option --output-stdlib-grades outputs the grades in which the Mercury standard library is available with this compiler.

• By default, the compiler now warns if the module being compiled has a name that shadows that of Mercury standard library module. The warning can be disabled using the new option --no-warn-stdlib-shadowing.

• The new options --output-java-class-dir and --output-java-class-directory are now supported as synonyms for --output-class-dir.

• The new option --halt-at-warn-make-interface causes the compiler to treat all warnings as if they were errors when generating interface files.

• The new option --halt-at-warn-make-opt causes the compiler to treat all warnings as if they were errors when generating optimization files.

• The new option --warn-potentially-ambiguous-pragma causes the compiler to generate a warning for all pragmas that include a name/arity pair, but lack a func() or pred() wrapper around it to indicate whether they are intended to apply to a function or to a predicate.

Portability improvements

• We have ported Mercury to Linux AArch64 (ARM64) systems.

• The tools/configure_mingw_cross script has been replaced by tools/configure_cross. It now supports aarch64-linux-gnu and aarch64-linux-musl as targets (i.e. Linux on aarch64 with GNU or musl C libraries).

Changes to the Mercury debugger

• The list command may now call an external command to print source listings; the command is set using list_cmd. For example, the command could produce syntax highlighted source listings.

• We have removed support for browsing terms as XML (browse --xml) as it was unmaintained and did not work any more. The browse --web command provides an alternative method for interactively exploring a term.

For news about earlier versions, see the HISTORY file.