19 Flags and Hooks

The following flags and hooks are available when Racket is embedded:

• scheme_exit — This pointer can be set to a function that takes an integer argument and returns void; the function will be used as the default exit handler. The default is NULL.

• scheme_make_stdin, scheme_make_stdout, scheme_make_stderr, — These pointers can be set to a function that takes no arguments and returns a Racket port Scheme_Object * to be used as the starting standard input, output, and/or error port. The defaults are NULL. Setting the initial error port is particularly important for seeing unexpected error messages if stderr output goes nowhere.

• scheme_console_output — This pointer can be set to a function that takes a string and a intptr_t string length; the function will be called to display internal Racket warnings and messages that possibly contain non-terminating nuls. The default is NULL.

• scheme_check_for_break — This points to a function of no arguments that returns an integer. It is used as the default user-break polling procedure in the main thread. A non-zero return value indicates a user break, and each time the function returns a non-zero value, it counts as a new break signal (though the break signal may be ignored if a previous signal is still pending). The default is NULL.

• scheme_case_sensitive — If this flag is set to a non-zero value before scheme_basic_env is called, then Racket will not ignore capitalization for symbols and global variable names. The value of this flag should not change once it is set. The default is zero.

• scheme_allow_set_undefined — This flag determines the initial value of compile-allow-set!-undefined. The default is zero.

• scheme_console_printf — This function pointer was left for backward compatibility. The default builds a string and calls scheme_console_output.

The function calls scheme_seal_parameters automatically.