19.1 Running racket and gracket

Depending on command-line arguments, racket or gracket runs in interactive mode, module mode, or load mode.

19.1.1 Interactive Mode

When racket is run with no command-line arguments (other than confguration options, like -j), then it starts a REPL with a >  prompt:

Welcome to Racket

>

For information on GNU Readline support, see readline.

To initialize the REPL’s environment, racket first requires the racket/init module, which provides all of racket, and also installs pretty-print for display results. Finally, racket loads the file reported by (find-system-path 'init-file), if it exists, before starting the REPL.

If any command-line arguments are provided (other than configuration options), add -i or --repl to re-enable the REPL. For example,

  racket -e '(display "hi\n")' -i

displays “hi” on start-up, but still presents a REPL.

If module-requiring flags appear before -i/--repl, they cancel the automatic requiring of racket/init. This behavior can be used to initialize the REPL’s environment with a different language. For example,

  racket -l racket/base -i

starts a REPL using a much smaller initial language (that loads much faster). Beware that most modules do not provide the basic syntax of Racket, including function-call syntax and require. For example,

  racket -l racket/date -i

produces a REPL that fails for every expression, because racket/date provides only a few functions, and not the #%top-interaction and #%app bindings that are needed to evaluate top-level function calls in the REPL.

If a module-requiring flag appears after -i/--repl instead of before it, then the module is required after racket/init to augment the initial environment. For example,

  racket -i -l racket/date

starts a useful REPL with racket/date available in addition to the exports of racket.

19.1.2 Module Mode

If a file argument is supplied to racket before any command-line switch (other than configuration options), then the file is required as a module, and (unless -i/--repl is specified), no REPL is started. For example,

  racket hello.rkt

requires the "hello.rkt" module and then exits. Any argument after the file name, flag or otherwise, is preserved as a command-line argument for use by the required module via current-command-line-arguments.

If command-line flags are used, then the -u or --require-script flag can be used to explicitly require a file as a module. The -t or --require flag is similar, except that additional command-line flags are processed by racket, instead of preserved for the required module. For example,

  racket -t hello.rkt -t goodbye.rkt

requires the "hello.rkt" module, then requires the "goodbye.rkt" module, and then exits.

The -l or --lib flag is similar to -t/--require, but it requires a module using a lib module path instead of a file path. For example,

  racket -l raco

is the same as running the raco executable with no arguments, since the raco module is the executable’s main module.

Note that if you wanted to pass command-line flags to raco above, you would need to protect the flags with a --, so that racket doesn’t try to parse them itself:

  racket -l raco -- --help

19.1.3 Load Mode

The -f or --load flag supports loading top-level expressions in a file directly, as opposed to expressions within a module file. This evaluation is like starting a REPL and typing the expressions directly, except that the results are not printed. For example,

  racket -f hi.rkts

loads "hi.rkts" and exits. Note that load mode is generally a bad idea, for the reasons explained in A Note to Readers with Lisp/Scheme Experience; using module mode is typically better.

The -e or --eval flag accepts an expression to evaluate directly. Unlike file loading, the result of the expression is printed, as in a REPL. For example,

  racket -e '(current-seconds)'

prints the number of seconds since January 1, 1970.

For file loading and expression evaluation, the top-level environment is created in the same way for interactive mode: racket/init is required unless another module is specified first. For example,

  racket -l racket/base -e '(current-seconds)'

likely runs faster, because it initializes the environment for evaluation using the smaller racket/base language, instead of racket/init.