The core PLT Scheme run-time system is available in two main variants:
MzScheme, which provides the primitives libraries on which scheme/base is implemented. Under Unix and Mac OS X, the executable is called mzscheme. Under Windows, the executable is called MzScheme.exe.
MrEd, which extends mzscheme with GUI primitives on which scheme/gui/base is implemented. Under Unix, the executable is called mred. Under Windows, the executable is called MrEd.exe. Under Mac OS X, the mred script launches MrEd.app.
On startup, the top-level environment contains no bindings – not even for function application. Primitive modules with names that start with #% are defined, but they are not meant for direct use, and the set of such modules can change. For example, the '#%kernel module is eventually used to bootstrap the implemetation of scheme/base, and '#%mred-kernel is used for scheme/gui/base.
The first action of MzScheme or MrEd is to initialize current-library-collection-paths to the result of (find-library-collection-paths extras), where extras are extra directory paths provided in order in the command line with -S/--search. An executable created from the MzScheme or MrEd executable can embed additional paths that are appended to extras.
MzScheme and MrEd next require scheme/init and scheme/gui/init, respectively, but only if the command line does not specify a require flag (-t/--require, -l/--lib, or -u/--require-script) before any eval, load, or read-eval-print-loop flag (-e/--eval, -f/--load, -r/--script, -m/--main, -i/--repl, or -z/--text-repl). The initialization library can be changed with the -I configuration option.
After potentially loading the initialization module, expression evals, files loads, and module requires are executed in the order that they are provided on the command line. If any raises an uncaught exception, then the remaining evals, loads, and requires are skipped.
After running all command-line expressions, files, and modules, MzScheme or MrEd then starts a read-eval-print loop for interactive evaluation if no command line flags are provided other than configuration options. If any command-line argument is provided that is not a configuration option, then the read-eval-print-loop is not started, unless the -i/--repl or -z/--text-repl flag is provided on the command line to specifically re-enable it. In addition, just before the command line is started, MzScheme loads the file (find-system-path 'init-file) and MrEd loads the file (find-graphical-system-path 'init-file) is loaded, unless the -q/--no-init-file flag is specified on the command line.
Finally, before MrEd exists, it waits for all frames to class, all timers to stop, etc. in the main eventspace by evaluating (scheme 'yield). This waiting step can be suppressed with the -V/--no-yield command-line flag.
The exit status for the MzScheme or MrEd process indicates an error if an error occurs during a command-line eval, load, or require when no read-eval-print loop is started. Otherwise, the exit status is 0 or determined by a call to exit.
The MzScheme and MrEd executables recognize the following command-line flags:
File and expression options:
-f 〈file〉 or --load 〈file〉 : loads 〈file〉.
-t 〈file〉 or --require 〈file〉 : requires 〈file〉.
-r 〈file〉 or --script 〈file〉 : loads 〈file〉 as a script. This flag is like -t 〈file〉 plus -N 〈file〉 to set the program name and -- to cause all further command-line elements to be treated as non-flag arguments.
-u 〈file〉 or --require-script 〈file〉 : requires 〈file〉 as a script; This flag is like -t 〈file〉 plus -N 〈file〉 to set the program name and -- to cause all further command-line elements to be treated as non-flag arguments.
-m or --main : Evaluates a call to main as bound in the top-level environment. All of the command-line arguments that are not processed as options (i.e., the arguments put into current-command-line-arguments) are passed as arguments to main. The results of the call are printed via current-print.
The call to main is constructed as an expression (main arg-str ...) where the lexical context of the expression gives #%app and #%datum bindings as #%plain-app and #%datum, but the lexical context of main is the top-level environment.
-i or --repl : Runs interactive read-eval-print loop, using either read-eval-print-loop (MzScheme) or graphical-read-eval-print-loop (MrEd) after showing (banner) and loading (find-system-path 'init-file).
-v or --version : Shows (banner).
-c or --no-compiled : Disables loading of compiled byte-code ".zo" files, by initializing current-compiled-file-paths to null.
-q or --no-init-file : Skips loading (find-system-path 'init-file) for -i/--repl or -z/--text-repl.
-X 〈dir〉 or --collects 〈dir〉 : Sets 〈dir〉 as the path to the main collection of libraries by making (find-system-path 'collects-dir) produce 〈dir〉.
-U or --no-user-path : Omits user-psecific paths in the search for collections, C libraries, etc. by initializing the use-user-specific-search-paths parameter to #f.
-N 〈file〉 or --name 〈file〉 : sets the name of the executable as reported by (find-system-path 'run-file) to 〈file〉.
-j or --no-jit : Disables the native-code just-in-time compiler by setting the eval-jit-enabled parameter to #f.
-d or --no-delay : Disables on-demand parsing of compiled code and syntax objects by setting the read-on-demand-source parameter to #f.
If at least one command-line argument is provided, and if the first one after any configuration option is not a flag, then a -u/--–require-script flag is implicitly added before the first non-flag argument.
If no command-line arguments are supplied other than configuration options, then the -i/--–repl flag is effectively added.
For MrEd under X11, the follow flags are recognized when they appear at the beginning of the command line, and they count as configuration options (i.e., they do not disable the read-eval-print loop or prevent the insertion of -u/--require-script):
-geometry 〈arg〉, -bg 〈arg〉, -background 〈arg〉, -fg 〈arg〉, -foreground 〈arg〉, -fn 〈arg〉, -font 〈arg〉, -iconic, -name 〈arg〉, -rv, -reverse, +rv, -selectionTimeout 〈arg〉, -synchronous, -title 〈arg〉, -xnllanguage 〈arg〉, or -xrm 〈arg〉 : Standard X11 arguments that are mostly ignored but accepted for compatibility with other X11 programs. The -synchronous and -xrm flags behave in the usual way.
-singleInstance : If an existing MrEd is already running on the same X11 display, if it was started on a machine with the same hostname, and if it was started with the same name as reported by (find-system-path 'run-file) – possibly set with the -N/--name command-line argument – then all non-option command-line arguments are treated as filenames and sent to the existing MrEd instance via the application file handler (see application-file-handler).
Similarly, under Mac OS X, a leading switch starting with -psn_ is treated as a special configuration option. It indicates that Finder started the application, so the current input, output, and error output are redirected to a GUI window.
Multiple single-letter switches (the ones preceded by a single -) can be collapsed into a single switch by concatenating the letters, as long as the first switch is not --. The arguments for each switch are placed after the collapsed switches (in the order of the switches). For example,
-ifve 〈file〉 〈expr〉
-i -f 〈file〉 -v -e 〈expr〉
are equivalent. If a collapsed -- appears before other collapsed switches in the same collapsed set, it is implicitly moved to the end of the collapsed set.
Extra arguments following the last option are available from the current-command-line-arguments parameter.