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(guile.info)libguile error handling

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libguile error handling
***********************

     Error handling is based on catch and throw.  Errors are always thrown with
     a key and four arguments:
     
     key: a symbol which indicates the type of error.  The symbols used
     by libguile are listed below.
     
     subr: the name of the procedure from which the error is thrown, or #f.
     
     message: a string (possibly language and system dependent) describing the
     error.  The tokens %s and %S can be embedded within the message: they
     will be replaced with members of the args list when the message is
     printed.  %s indicates an argument printed using "display", while %S
     indicates an argument printed using "write".  message can also be #f,
     to allow it to be derived from the key by the error handler (may be
     useful if the key is to be thrown from both C and Scheme).
     
     args: a list of arguments to be used to expand %s and %S tokens in message.
     Can also be #f if no arguments are required.
     
     rest: a list of any additional objects required. e.g., when the key is
     'system-error, this contains the C errno value.  Can also be #f if no
     additional objects are required.
     
     In addition to catch and throw, the following Scheme facilities are
     available:
     
     (scm-error key subr message args rest): throw an error, with arguments
     as described above.
     
     (error msg arg ...)  Throw an error using the key 'misc-error.  The error
     message is created by displaying msg and writing the args.
     
     The following are the error keys defined by libguile and the situations
     in which they are used:
     
     error-signal: thrown after receiving an unhandled fatal signal such as
     SIGSEV, SIGBUS, SIGFPE etc.  The "rest" argument in the throw contains
     the coded signal number (at present this is not the same as the usual
     Unix signal number).
     
     system-error: thrown after the operating system indicates an error
     condition.  The "rest" argument in the throw contains the errno value.
     
     numerical-overflow: numerical overflow.
     
     out-of-range: the arguments to a procedure do not fall within the
     accepted domain.
     
     wrong-type-arg: an argument to a procedure has the wrong thpe.
     
     wrong-number-of-args: a procedure was called with the wrong number of
     arguments.
     
     memory-allocation-error: memory allocation error.
     
     stack-overflow: stack overflow error.
     
     regex-error: errors generated by the regular expression library.
     
     misc-error: other errors.
     
     C support
     =========
     
     SCM scm_error (SCM key, char *subr, char *message, SCM args, SCM rest)
     
     Throws an error, after converting the char * arguments to Scheme strings.
     subr is the Scheme name of the procedure, NULL is converted to #f.
     Likewise a NULL message is converted to #f.
     
     The following procedures invoke scm_error with various error keys and
     arguments.  The first three call scm_error with the system-error key
     and automatically supply errno in the "rest" argument:  scm_syserror
     generates messages using strerror,  scm_sysmissing is used when
     facilities are not available.  Care should be taken that the errno
     value is not reset (e.g., due to an interrupt.)
     
     void scm_syserror (char *subr);
     void scm_syserror_msg (char *subr, char *message, SCM args);
     void scm_sysmissing (char *subr);
     
     void scm_num_overflow (char *subr);
     void scm_out_of_range (char *subr, SCM bad_value);
     void scm_wrong_num_args (SCM proc);
     void scm_wrong_type_arg (char *subr, int pos, SCM bad_value);
     void scm_memory_error (char *subr);
     static void scm_regex_error (char *subr, int code); (only used in rgx.c).
     
     Exception handlers can also be installed from C, using
     scm_internal_catch, scm_lazy_catch, or scm_stack_catch from
     libguile/throw.c.  These have not yet been documented, however the
     source contains some useful comments.