Chapter 11

Running MrEd

MrEd accepts a number of command-line flags.

Under Mac OS Classic, a user can specify command-line flags by holding down the Command key while starting MrEd, which provides a dialog for entering the command line. Dragging files onto the MrEd icon in Mac OS Classic is equivalent to providing each file's name on the command line preceded by -f, so each file is loaded after MrEd starts. When files are dragged onto MrEd with the Command key pressed, the command line specified in the dialog is appended to the implicit command-line for loading the files.

Under Mac OS X, a leading flag of the form -psn_ is treated specially. It indicates that Finder started the application, so the current input, output, and error output are redirected to a GUI window.

MrEd accepts the following flags (in addition to the X-specific flags described in X Window System Flags):

11.1  Flag Conventions

Extra arguments following the last flag are available from the current-command-line-arguments parameter (see Images, section in PLT MzScheme: Language Manual) as an immutable vector of immutable strings. The name used to start MrEd is available from the find-system-path procedure (see Images, section 11.3.1 in PLT MzScheme: Language Manual) using 'exec-file. In addition, unless -A is specified, the argument vector is put into the global variable argv, and the name used to start MrEd is put into the global variable program as an immutable string.

Multiple single-letter flags (the ones preceded by a single dash) can be collapsed into a single flag by concatenating the letters, as long as the the first flag is not --. The arguments for each flag are placed after the collapsed flags (in the order of the flags). For example,

   -vfme file expr


   -v -f file -m -e expr

are equivalent. If a collapsed -- appears before other collapsed flags, it is implicitly moved to the end of the collapsed set.

11.2  Executable Name

If the MrEd executable is given a name of the form scheme-dialect, then the command line is effectively prefixed with

   -qAeC '(require (lib "" "script-lang" "dialect"))'

The first actual command-line argument thus serves as a file to load. The file is loaded into a namespace that is initialized by the dialect-specific library. The loaded file should define main, which is called with command-line arguments -- starting with the loaded file name -- as a list of immutable strings.

11.3  Initialization

The current-library-collection-paths parameter is initialized (as described in Library Collections and MzLib, section 16 in PLT MzScheme: Language Manual) before any expression or file is evaluated or loaded, unless the -x or --no-lib-path flag is specified.

Unless the -q or --no-init-file flag is specified, a user initialization file is loaded after current-library-collection-paths parameter is initialized and before any other expression or file is evaluated or loaded. The path to the user initialization file is obtained from MzScheme's find-system-path procedure using 'init-file.

Expressions and files are evaluated and loaded in order that they are provided on the command line, including calls to main implied by --main, embeddings loaded by -k, and so on. If an uncaught exception occurs, the remaining expressions and files are skipped. The thread that loads the files and evaluates the expressions is the main thread. When the main thread terminates (or is killed), the MrEd process exits. The main thread is also the handler thread of the initial eventspace.

After the command-line files and expressions are loaded and evaluated, the main thread calls graphical-read-eval-print-loop, unless the -v, --version, -r, --script, -i, or --script-cd flag is specified. The -z or --stdio flag also suppresses the call to graphical-read-eval-print-loop, but it calls read-eval-print-loop, instead. (The other flags, such as -v, have no effect on this call to read-eval-print-loop.)

Finally, after the command-line files and expressions are loaded and evaluated, and after graphical-read-eval-print-loop or read-eval-print-loop is called, the main thread evaluates (yield 'wait). The -V or --no-yield flag suppresses this call to yield.

The exit status for the MrEd process indicates an error if an error occurs evaluating or loading a command-line expression or file and graphical-read-eval-print-loop is not called afterwards, or if the default exit handler is called with an exact integer between 1 and 255.

Evaluating command-line expressions with -f or -v is different from evaluating the same expressions within the window provided by graphical-read-eval-print-loop. The graphical-read-eval-print-loop window creates a new eventspace (and thus a new thread) for evaluating expressions entered into the window. One consequence of this convention is that terminating the evaluation thread (e.g., with (kill-thread (current-thread))) does not cause MrEd to exit, because the evaluation thread is not MrEd's main thread.18

In contrast, MzScheme's read-eval-print-loop always evaluates expressions within the thread that calls read-eval-print-loop. Using the -z or --stdio flag calls read-eval-print-loop in the main thread, so (kill-thread (current-thread)) in that case does exit MrEd. Furthermore, the main thread is the handler thread for the initial eventspace; thus, windows created in read-eval-print-loop without changing the eventspace never receive events unless (yield) is called explicitly.

11.4  Initial Eventspace

MrEd creates an initial eventspace, and the handler thread for the eventspace is MrEd's main thread; if the thread is killed, then the MrEd process exits.

11.5  X Window System Flags

Under Unix/X, the following standard X Window System flags are recognized (but not necessarily implemented): -display (1 argument), -geometry (1 argument), -bg (1 argument), -background (1 argument), -fg (1 argument), -foreground (1 argument), -fn (1 argument), -font (1 argument), -iconic (0 arguments), -name (1 argument), -rv (0 argument), -reverse (0 arguments), +rv (0 arguments), -selectionTimeout (1 argument), -synchronous (0 arguments), -title (1 argument), -xnllanguage (1 argument), and -xrm (1 argument).

All X flags must precede all other flags and arguments.

18 However, the exit handler is not changed, so evaluating (exit) does exit MrEd unless the exit handler is changed before calling graphical-read-eval-print-loop.