Inform 6.41

A new release of Inform 6, version 6.40, is now available from the Inform 6 Github project, and from the IF-Archive: Release notes, source code and Windows console executable.

Credit for virtually all of these changes goes to Andrew Plotkin.

Features added

  • The various command line arguments that produce tracing or statistical information have been consolidated in a new argument: $!TRACEOPT or $!TRACEOPT=N. The Unix-style equivalent is --trace TRACEOPT or --trace TRACEOPT=N. You can also use $! by itself (or --helptrace) to list all available trace options. Trace option names are case-insensitive.

    The optional N is always an integer. 0 always means off, 1 is the base level, 2 or more may increase verbosity. As a general rule, setting N to a high number is not an error; it just does the same thing as the highest supported number for that option. (This lets us add more verbosity levels to any option without worrying about compatibility errors.)

    Four trace settings can be changed in mid-compile with the Trace directive. (This has always been true but now it is handled consistently.) Trace assembly, Trace expressions, Trace tokens and Trace linker are equivalent to --trace asm, --trace expr, --trace tokens and --trace linker, respectively. As with the command-line versions, you can optionally specify 0 to turn off that setting or 2 or more for more verbosity.

    Four more trace directives do an immediate information dump: Trace dictionary, Trace objects, Trace symbols and Trace verbs. The command-line equivalents --trace dict, --trace objects, --trace symbols and --trace verbs do the same at the end of compilation.

    The following single-letter options have been removed and replaced with trace options:

    • -j: Replaced by --trace OBJECTS
    • -m: Replaced by --trace MEM
    • -n: Replaced by --trace PROPS (for property information) and --trace ACTIONS (for action numbers)
    • -p: Replaced by --trace MAP=2
    • -t: Replaced by --trace ASM=2
    • -y: Replaced by --trace LINKER

    The following single-letter options still exist, but are now aliases for trace options:

    • -a: Same as --trace ASM
    • -f: Same as --trace FREQ
    • -g: Same as --trace RUNTIME
    • -s: Same as --trace STATS
    • -z: Same as --trace MAP

    The following single-letter options have been removed entirely:

    • -b: Has not done anything since at least Inform 5.
    • -l: Was supposed to list all statements compiled, but it was never implemented.
    • -o: Showed the same information as -z or --trace MAP.

    The -l option did show include files being opened; this is now a separate trace setting, --trace FILES.

    Some of the information that used to be under -a4 is now a separate trace setting, --trace BPATCH.

  • The -u option now just outputs computed abbreviations. If you want the verbose calculation information that it used to print, use --trace FINDABBREVS or --trace FINDABBREVS=2.

  • The compiler is now capable of dead code elimination, allowing it to:

    • Discard unreachable opcodes and strings.
    • Minimize generated code for dead branches (if (0), if (1)).
    • Detect if and switch statements where every branch returns.
    • Detect loops that never exit (or always return).
    • Discard @jz constant opcodes where the constant is non-zero.
    • Convert @jz 0 to an unconditional @jump.
    • Discard a @jump to the very next instruction.
    • Discard store opcodes when computing a logical expression as a value, if one case (0 or 1) is impossible.
    • Fold expressions like (0 && expr) and (1 || expr), even when expr is not a constant.

    When statements that can never be reached are eliminated, a warning is produced, where appropriate.

    Dead code elimination does mean that theoretically possible (though very odd) valid code will now result in a compilation error. For example,

  if (DOSTUFF) {
    while (condition) {
  jump MiddleLabel; ! error

This will fail with a compilation error if DOSTUFF is defined as a constant zero. This optimization can be turned off by setting the compiler setting $STRIP_UNREACHABLE_LABELS to zero (its default is one).

  • There are now further warnings if the compiler detects that the type used in certain expressions is not correct:

    • X(), indirect(X): X must be a routine
    • X.Y, X.&Y, X.#Y: X must be a class or an object; Y must be a property (the Y checks already existed)
    • X.Y(): X must be a class, object, string or routine; Y must be a property
    • X.Y++, X.Y--, ++X.Y, --X.Y: X must be a class or an object; Y must be a property
  • There is a new syntax for dynamic-string interpolations: "@(N)". The original syntax was "@NN", which is still supported. In the new syntax "N" can be a number, or an already defined numeric constant. As a result of this, under Glulx the limit on $MAX_DYNAMIC_STRINGS being less than 100 has been removed.

  • The constants #dictionary_table and #grammar_table are now available when compiling to Z-code, as well as Glulx.

  • The command line switch to display percentages (-p) now works with Glulx, and acts as an extension to the -z switch.

  • The double precision floating point related opcodes added to the Glulx 3.1.3 specification (that is, @numtod, @dtonumz, @dtonumn, @ftod, @dtof, @dceil, @dfloor, @dadd, @dsub, @dmul, @ddiv, @dmodr, @dmodq, @dsqrt, @dexp, @dlog, @dpow, @dsin, @dcos, @dtan, @dasin, @dacos, @datan, @datan2, @jdeq, @jdne, @jdlt, @jdle, @jdgt, @jdge, @jdisnan, @jdisinf) are now supported. In addition there are also two new macros @dload and @dstore, to load and store double precision floating point values.

  • The undo related opcodes added to the Glulx 3.1.3 specification (that is, @hasundo and @discardundo) are now supported.

  • The Version and Switches directives are now deprecated, and produce a warning if used. The recommended way to set the Z-code version and any other switches is to use the command line, or !% comments at the top of the source file.

  • The ability to compile Inform source code as modules, and then later link it, has been removed. This functionality always had significant restrictions and was never widely used. The -M and -U command line options have been removed, along with the +module_path option. The Link and Import directives now just produce errors.

  • The ability to use temporary files for internal storage (the -F switch and the +temporary_path option) have been removed.

  • The = sign in the Global directive is now optional, just as it is in the Constant directive. So all of these are now legal:

  Constant c1 11;
  Constant c2 = 22;
  Global g1 33;
  Global g2 = 44;
  • The long deprecated forms of the Global directive that could define arrays have been removed. All these are now no longer legal:
  Global array --> size;
  Global array data ...;
  Global array initial ...;
  Global array initstr ...;

Bugs fixed

  • Abbreviation directives now only add abbreviations to the output file if economy mode (-e) is set.

  • An array overrun when the $ZCODE_LESS_DICT_DATA setting is enabled has been fixed.

  • The logic that allows a test for the compiler version of the form #IfDef VN_1640 now requires what follows the “VN_” to be a number.


The tag for 6.40 is a little weird: v.640, when it should probably be v6.40 if following the existing scheme.

I’ve brought the Inform 6 Reference Addendum up to date with this release. Let me know if there’s anything unclear.


Oops, fat finger moment when creating the git tag. Now fixed, the actual release and the git history are unchanged.

1 Like

An issue has shown up with Inform 6.40: the new dead code elimination logic can cause a problem with Inform 6 code generated by the Inform 7 compiler in the case of a forward jump inside a for() loop. Zarf has improved the DCE logic to allow this case, so it’s time for Inform 6.41 …

A new release of Inform 6, version 6.41, is now available from the Inform 6 Github project, and from the IF-Archive: Release notes, source code and Windows console executable.

Features added

  • The dead code elimination logic now allows forward jumps to labels that would be otherwise unreachable, like this:
  if (condition) {
    jump MiddleLabel;
  if (0) {
    while (condition) {
  • The error that occurs when the compiler encounters a jump to an unknown label now includes the name of that label.