Mercury inherited its original system of operator priorities from Prolog,
because during its initial development, we wanted to be able execute
the Mercury compiler using NU-Prolog and later SICStus Prolog.
That consideration has long been obsolete, and now we may fix the
design error that gifted Prolog with its counter-intuitive system
of operator priorities, in which higher *numerical* operator priorities
mean lower *actual* priorities. This diff does that.
library/ops.m:
Change the meaning of operator priorities, to make higher numerical
priorities mean also higher actual priorities.
This semantic change requires corresponding changes in any other module
that uses ops.m. To force this change to occur, change the type
representing priorities from being a synonym for a bare int to being
a notag wrapper around an uint.
The old "assoc" type had a misleading name, since it is related to
associativity but is not itself a representation of associativity.
Its two function symbols, which used to be just "x" and "y", meant that
the priority of an argument must be (respectively) greater than,
or greater than equal to, the priority of the operator. So rename
x to arg_gt, y to arg_ge, and assoc to arg_prio_gt_or_ge.
Rename the old adjust_priority_for_assoc predicate to min_priority_for_arg,
which better expresses its semantics. Turn it into a function, since
some of its users want it that way, and move its declaration to the
public part of the interface.
Add a method named tightest_op_priority to replace the use of 0
as a priority.
Rename the max_priority method as the loosest_op_priority method.
Add a method named universal_priority to replace the use of
max_priority + 1 as a priority.
Add a function to return the priority of the comma operator,
to allow other modules to stop hardcoding it.
Add operations for comparing priorities and for incrementing/decrementing
priorities.
Change the prefix on the names of the predicates that take op_infos
as inputs from "mercury_op_table_" to "op_infos_", since the old prefix
was misleading.
Add a note on an significant old problem with an exported type synonym.
library/mercury_term_parser.m:
Conform to the changes above.
Delete unnecessary module qualifiers, since they were just clutter.
Add "XXX OPS" to note further opportunities for improvement.
library/pprint.m:
Conform to the changes above.
Rename a function to avoid ambiguity.
library/pretty_printer.m:
library/stream.string_writer.m:
library/string.to_string.m:
library/term_io.m:
Conform to the changes above.
library/string.m:
Add a note on an significant old problem.
NEWS:
Announce the user-visible changes.
tests/hard_coded/bug383.m:
Update this test case to use the new system of operator priorities.
tests/hard_coded/term_io_test.{m,inp}:
Fix white space.
extras/old_library_modules/old_mercury_term_parser.m:
extras/old_library_modules/old_ops.m:
The old contents of the mercury_term_parser and ops modules,
in case anyone wants to continue using them instead of updating
their code to use their updated equivalents.
samples/calculator2.m:
Import the old versions of mercury_term_parser and ops.
Their replacements are the corresponding predicates in mercury_term_parser.m,
which they forwarded all their work to anyway.
library/term_io.m:
As above.
library/mercury_term_parser.m:
Move the definition of a type needed by the read_term* predicates
here from term_io.m.
NEWS:
Document the deletion.
browser/interactive_query.m:
compiler/fact_table.m:
compiler/parse_module.m:
compiler/recompilation.used_file.m:
library/io.m:
Conform to the change above.
tests/debugger/interpreter.m:
tests/general/interpreter.m:
Use read_term* from mercury_term_parser, not term_io.
These two tests started out as versions of the same file once upon a time,
but have diverged since. Replace them both with a single version that
works in both test directories, and has updated programming style.
tests/debugger/interpreter.exp2:
tests/debugger/interpreter.inp:
tests/general/interpreter.exp:
Conform to the changes (renames of some predicates, inlining of others,
using explicit streams, never complaining about empty argument lists,
and always printing query results) in interpreter.m.
tests/hard_coded/bug383.m:
tests/hard_coded/term_io_test.m:
Use read_term* from mercury_term_parser, not term_io.
In bug383.m, resolve an old type ambiguity to avoid a warning.
tests/hard_coded/*.m:
Update programming style, unless doing so would change
the meaning of the test, in particular:
- use '.' as a module qualifier in place of '__'
- use {write,print}_line where appropriate
- use if-then-else in place of C -> T ; E
- use state variables in place of DCGs
tests/hard_coded/dir_test.m:
Document what the expected outputs correspond to.
Use a uniform module qualifier in the output.
tests/hard_coded/dir_test.exp*:
Conform to the above change.
tests/accumulator/*.m:
tests/analysis_*/*.m:
tests/benchmarks*/*.m:
tests/debugger*/*.{m,exp,inp}:
tests/declarative_debugger*/*.{m,exp,inp}:
tests/dppd*/*.m:
tests/exceptions*/*.m:
tests/general*/*.m:
tests/grade_subdirs*/*.m:
tests/hard_coded*/*.m:
Make these tests use four-space indentation, and ensure that
each module is imported on its own line. (I intend to use the latter
to figure out which subdirectories' tests can be executed in parallel.)
These changes usually move code to different lines. For the debugger tests,
specify the new line numbers in .inp files and expect them in .exp files.
Estimated hours taken: 5
Branches: main
Fix a bug reported by Doug Auclair.
library/ops.m:
Change the Mercury arg priority to 999. It was previously set to
1201, which allowed arguments and list elements to be parsed the
way we intended. However, this had the unintended side effect that
valid terms were written out using incorrect syntax.
library/parser.m:
Place the workaround here, where arguments and list elements are
read.
Note that this is still technically buggy, because we effectively
allow syntax which should be illegal according to the operator
precedence table. But the proper fix for this involves moving to
a BNF style parser, so that is left for later work.
tests/hard_coded/Mmakefile:
Run the term_io_test case twice, checking it against the expected
output each time. The first time it is run with the supplied input
file. The second time it is run with the expected output as input --
this ensures that terms are read in the same way that they are
written out.
tests/hard_coded/term_io_test.m:
Read input from stdin rather than a fixed file.
tests/hard_coded/term_io_test.inp:
Add additional input terms.
tests/hard_coded/term_io_test.exp:
tests/invalid/*.err_exp:
Update the expected output for this and other test cases.
Estimated hours taken: 0.25
tests/hard_coded/term_io_test.m:
Add this file; conway forgot to `cvs add' it before he committed
his recent change which was supposed to add it.
