[m-rev.] for review: add io.write_prefixed_lines/[45]

[Julien Fischer]

This is a follow-up to my post to the m-dev list the other week.
Looking further into how we generate usage and version messages, there
is not any consistency among the programs in the Mercury system. This
change is the first in a series of changes to provide such consistency.

-------------------------------------------------

Add io.write_prefixed_lines/[45].

This is a generalisation of the write_tabbed_lines predicate that mmc
and mcov use to print their usage messages. (In a later change other
programs in the Mercury system will be changed to use it as well.)

library/io.m:
     Add the new predicates.

compiler/options.m:
slice/mcov.m:
     Use write_prefixed_lines in place of write_tabbed lines
     and delete the latter.

NEWS.md:
     Announce the addition.

Julien.

diff --git a/NEWS.md b/NEWS.md
index e489864..71152f9 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -319,6 +319,8 @@ Changes to the Mercury standard library
      - 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:

diff --git a/compiler/options.m b/compiler/options.m
index 41fff3f..398532a 100644
--- a/compiler/options.m
+++ b/compiler/options.m
@@ -4178,7 +4178,7 @@ options_help(Stream, !IO) :-

  options_help_warning(Stream, !IO) :-
      io.write_string(Stream, "\nWarning Options:\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "-w, --inhibit-warnings",
          "\tDisable all warning messages.",
          "--inhibit-style-warnings",
@@ -4441,7 +4441,7 @@ options_help_warning(Stream, !IO) :-

  options_help_verbosity(Stream, !IO) :-
      io.write_string(Stream, "\nVerbosity Options:\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "-v, --verbose",
          "\tOutput progress messages at each stage in the compilation.",
          "-V, --very-verbose",
@@ -4585,7 +4585,7 @@ options_help_verbosity(Stream, !IO) :-

  options_help_output(Stream, !IO) :-
      io.write_string(Stream, "\nOutput Options:\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "These options are mutually exclusive.",
          "Only the first one specified will apply.",
          "If none of these options are specified, the default action",
@@ -4711,7 +4711,7 @@ options_help_output(Stream, !IO) :-

  options_help_aux_output(Stream, !IO) :-
      io.write_string(Stream, "\nAuxiliary Output Options:\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
  % These are commented out until the compiler consistently does
  % what these options say it should do when specified.
  %       "--error-output-suffix .xyz",
@@ -5036,7 +5036,7 @@ options_help_semantics(Stream, !IO) :-
          "(See the Mercury language reference manual ", !IO),
      io.write_string(Stream,
          "for detailed explanations.)\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "--no-reorder-conj",
          "\tExecute conjunctions left-to-right except where the modes imply",
          "\tthat reordering is unavoidable.",
@@ -5076,7 +5076,7 @@ options_help_semantics(Stream, !IO) :-
  options_help_ctgc(Stream, !IO) :-
      io.write_string(Stream,
          "\nCompile Time Garbage Collection Options:\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "--structure-sharing",
          "\tPerform structure sharing analysis.",
          "--structure-sharing-widening <n>",
@@ -5116,7 +5116,7 @@ options_help_ctgc(Stream, !IO) :-

  options_help_termination(Stream, !IO) :-
      io.write_string(Stream, "\nTermination Analysis Options:\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "--enable-term, --enable-termination",
          "\tAnalyse each predicate to discover if it terminates.",
          "--chk-term, --check-term, --check-termination",
@@ -5195,7 +5195,7 @@ options_help_termination(Stream, !IO) :-

  options_help_compilation_model(Stream, !IO) :-
      io.write_string(Stream, "\nCompilation model options:\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "The following compilation options affect the generated",
          "code in such a way that the entire program must be",
          "compiled with the same setting of these options,",
@@ -5203,7 +5203,7 @@ options_help_compilation_model(Stream, !IO) :-
          "library which has been compiled with the same setting."
      ], !IO),
      io.write_string(Stream, "\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "-s <grade>, --grade <grade>",
          "\tSelect the compilation model. The <grade> should be one of",
          "\tthe base grades `none', `reg', `asm_fast', `hlc', `java' or,",
@@ -5233,7 +5233,7 @@ options_help_compilation_model(Stream, !IO) :-

      io.write_string(Stream,
          "\n    Target selection compilation model options:\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          %"--target c\t\t\t(grades: none, reg, jump, fast,",
          %"\t\t\t\t\tasm_jump, asm_fast, hl, hlc)",
          "--target c\t\t\t(grades: none, reg, asm_fast, hlc)",
@@ -5267,7 +5267,7 @@ options_help_compilation_model(Stream, !IO) :-
          "\n    Optional feature compilation model options:\n", !IO),
      io.write_string(Stream,
          "\n      Debugging\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "--debug\t\t\t\t(grade modifier: `.debug')",
          "\tEnable Mercury-level debugging.",
          "\tSee the Debugging chapter of the Mercury User's Guide",
@@ -5289,7 +5289,7 @@ options_help_compilation_model(Stream, !IO) :-
      ], !IO),
      io.write_string(Stream,
          "\n      Profiling\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "-p, --profiling, --time-profiling",
          "\t\t\t\t(grade modifier: `.prof')",
          "\tEnable time and call profiling. Insert profiling hooks in the",
@@ -5397,7 +5397,7 @@ options_help_compilation_model(Stream, !IO) :-

      io.write_string(Stream,
          "\n      Miscellaneous optional features\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "--gc {none, boehm, hgc, accurate, automatic}",
          "--garbage-collection {none, boehm, hgc, accurate, automatic}",
          "\t\t\t\t(`java' and `csharp' grades",
@@ -5450,7 +5450,7 @@ options_help_compilation_model(Stream, !IO) :-

      io.write_string(Stream,
          "\n    LLDS back-end compilation model options:\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          %"--gcc-global-registers\t\t(grades: reg, fast, asm_fast)",
          %"--no-gcc-global-registers\t(grades: none, jump, asm_jump)",
          "--gcc-global-registers\t\t(grades: reg, asm_fast)",
@@ -5489,7 +5489,7 @@ options_help_compilation_model(Stream, !IO) :-

      io.write_string(Stream,
          "\n    MLDS back-end compilation model options:\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "-H, --high-level-code\t\t\t(grades: hlc, csharp, java)",
          "\tUse an alternative back-end that generates high-level code",
          "\trather than the very low-level code that is generated by our",
@@ -5531,7 +5531,7 @@ options_help_compilation_model(Stream, !IO) :-
          "\n    Developer compilation model options:\n", !IO),
      io.write_string(Stream,
          "\n      Data representation\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "--num-ptag-bits <n>           (This option is not for general use.)",
          "\tUse <n> primary tag bits."
          % Normally, The --num-tag-bits option is used only by the compiler.
@@ -5595,7 +5595,7 @@ options_help_compilation_model(Stream, !IO) :-
      ], !IO),
      io.write_string(Stream,
          "\n      Developer optional features\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "--use-minimal-model-stack-copy",
          "(This option is not for general use.)",
          "\tEnable the use of the standard form of minimal model tabling.",
@@ -5713,7 +5713,7 @@ options_help_compilation_model(Stream, !IO) :-

  options_help_code_generation(Stream, !IO) :-
      io.write_string(Stream, "\nCode generation options:\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
  %       "--table-debug",
  %       "\tEnables the generation of code that helps to debug tabling",
  %       "\tprimitives.",
@@ -5805,7 +5805,7 @@ options_help_code_generation(Stream, !IO) :-
      ], !IO),

      io.write_string(Stream, "\n    Code generation target options:\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "--branch-delay-slot    \t(This option is not for general use.)",
          "\tAssume that branch instructions have a delay slot.",
          "--num-real-r-regs <n>  \t(This option is not for general use.)",
@@ -5827,7 +5827,7 @@ options_help_code_generation(Stream, !IO) :-

  options_help_optimization(Stream, !IO) :-
      io.write_string(Stream, "\nOptimization Options:\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          % This is for use by Mercury.config only.
      %   "--default-opt-level -O<n>",
      %   "\tSet the default optimization level to <n>.",
@@ -5886,7 +5886,7 @@ options_help_optimization(Stream, !IO) :-
  options_help_hlds_hlds_optimization(Stream, !IO) :-
      io.write_string(Stream,
          "\n    High-level (HLDS -> HLDS) optimizations:\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "--no-inlining",
          "\tDisable all forms of inlining.",
          "--no-inline-simple",
@@ -6152,7 +6152,7 @@ options_help_hlds_hlds_optimization(Stream, !IO) :-
  options_help_hlds_llds_optimization(Stream, !IO) :-
      io.write_string(Stream,
          "\n    Medium-level (HLDS -> LLDS) optimizations:\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "--no-smart-indexing",
          "\tGenerate switches as simple if-then-else chains;",
          "\tdisable string hashing and integer table-lookup indexing.",
@@ -6229,7 +6229,7 @@ options_help_hlds_llds_optimization(Stream, !IO) :-
  options_help_llds_llds_optimization(Stream, !IO) :-
      io.write_string(Stream,
          "\n    Low-level (LLDS -> LLDS) optimizations:\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "--no-common-data",
          "\tDisable optimization of common data structures.",
          "--no-common-layout-data",
@@ -6288,7 +6288,7 @@ options_help_llds_llds_optimization(Stream, !IO) :-

  options_help_mlds_mlds_optimization(Stream, !IO) :-
      io.write_string(Stream, "\n    MLDS -> MLDS optimizations:\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "--no-mlds-optimize",
          "\tDisable the MLDS->MLDS optimization passes.",
          "--no-mlds-peephole",
@@ -6318,7 +6318,7 @@ options_help_mlds_mlds_optimization(Stream, !IO) :-
  options_help_output_optimization(Stream, !IO) :-
      io.write_string(Stream,
          "\n    Output-level (LLDS -> C) optimizations:\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "--use-macro-for-redo-fail",
          "\tEmit the fail or redo macro instead of a branch",
          "\tto the fail or redo code in the runtime system.",
@@ -6347,7 +6347,7 @@ options_help_output_optimization(Stream, !IO) :-

  options_help_target_code_compilation(Stream, !IO) :-
      io.write_string(Stream, "\n    Target code compilation:\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "\tNote that if you are using Mmake, you need to pass these",
          "\toptions to the target code compiler (e.g. `mgnuc')",
          "\trather than to `mmc'.",
@@ -6444,7 +6444,7 @@ options_help_target_code_compilation(Stream, !IO) :-

  options_help_link(Stream, !IO) :-
      io.write_string(Stream, "\nLink Options:\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "-o <filename>, --output-file <filename>",
          "\tSpecify the name of the final executable.",
          "\t(The default executable name is the same as the name",
@@ -6619,7 +6619,7 @@ options_help_link(Stream, !IO) :-

  options_help_build_system(Stream, !IO) :-
      io.write_string(Stream, "\nBuild System Options:\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "-m, --make",
          "\tTreat the non-option arguments to `mmc' as files to make,",
          "\trather than source files. Build or rebuild the specified files",
@@ -6781,7 +6781,7 @@ options_help_build_system(Stream, !IO) :-

  options_help_misc(Stream, !IO) :-
      io.write_string(Stream, "\nMiscellaneous Options:\n", !IO),
-    write_tabbed_lines(Stream, [
+    io.write_prefixed_lines(Stream, "\t", [
          "--filenames-from-stdin",
          "\tRead then compile a newline terminated module name or",
          "\tfile name from the standard input. Repeat this until EOF",
@@ -6837,14 +6837,6 @@ options_help_misc(Stream, !IO) :-
          "\tonly be processed for implicit parallelism."
      ], !IO).

-:- pred write_tabbed_lines(io.text_output_stream::in, list(string)::in,
-    io::di, io::uo) is det.
-
-write_tabbed_lines(_, [], !IO).
-write_tabbed_lines(Stream, [Str | Strs], !IO) :-
-    io.format(Stream, "\t%s\n", [s(Str)], !IO),
-    write_tabbed_lines(Stream, Strs, !IO).
-
  %---------------------------------------------------------------------------%
  :- end_module libs.options.
  %---------------------------------------------------------------------------%
diff --git a/library/io.m b/library/io.m
index e9dd168..e2c91a5 100644
--- a/library/io.m
+++ b/library/io.m
@@ -1210,6 +1210,18 @@
  :- pred write_strings(io.text_output_stream::in, list(string)::in,
      io::di, io::uo) is det.

+    % write_prefixed_lines(Prefix, Lines, !IO):
+    % write_prefixed_lines(Stream, Prefix, Lines, !IO):
+    %
+    % Write each line in Lines to the current output stream or to the
+    % specified output stream. Write Prefix before each line and write
+    % a newline after each line.
+    %
+:- pred write_prefixed_lines(string::in, list(string)::in, io::di, io::uo)
+    is det.
+:- pred write_prefixed_lines(io.text_output_stream::in, string::in,
+    list(string)::in, io::di, io::uo) is det.
+
      % Writes the specified arguments to the current output stream
      % or to the specified output stream.
      %
@@ -3824,6 +3836,17 @@ write_strings(Stream, [S | Ss], !IO) :-

  %---------------------%

+write_prefixed_lines(Prefix, Lines, !IO) :-
+    io.output_stream(Stream, !IO),
+    write_prefixed_lines(Stream, Prefix, Lines, !IO).
+
+write_prefixed_lines(_, _, [], !IO).
+write_prefixed_lines(Stream, Prefix, [Str | Strs], !IO) :-
+    io.format(Stream, "%s%s\n", [s(Prefix), s(Str)], !IO),
+    write_prefixed_lines(Stream, Prefix, Strs, !IO).
+
+%---------------------%
+
  write_many(Vals, !IO) :-
      io.output_stream(Stream, !IO),
      write_many(Stream, Vals, !IO).
diff --git a/slice/mcov.m b/slice/mcov.m
index 50facc2..9294316 100644
--- a/slice/mcov.m
+++ b/slice/mcov.m
@@ -462,7 +462,7 @@ long_usage(OutStream, !IO) :-
      io.write_string(OutStream,
          "\tArguments are assumed to Mercury trace count files.\n", !IO),
      io.write_string(OutStream, "Options:\n", !IO),
-    write_tabbed_lines(OutStream, [
+    io.write_prefixed_lines(OutStream, "\t", [
          "-?, -h, --help",
          "\tPrint help about using mcov (on the standard output) and exit",
          "\twithout doing any further processing.",
@@ -489,14 +489,6 @@ long_usage(OutStream, !IO) :-
          %"\treports.".
      ], !IO).

-:- pred write_tabbed_lines(io.text_output_stream::in, list(string)::in,
-    io::di, io::uo) is det.
-
-write_tabbed_lines(_OutStream, [], !IO).
-write_tabbed_lines(OutStream, [Str | Strs], !IO) :-
-    io.format(OutStream, "\t%s\n", [s(Str)], !IO),
-    write_tabbed_lines(OutStream, Strs, !IO).
-
  %---------------------------------------------------------------------------%

  :- type option