- Members are volatile if their values need to survive _longjmp when
- a 'struct handler' is a local variable. */
-struct handler
- {
- /* The handler clauses and variable from the condition-case form. */
- /* For a handler set up in Lisp code, this is always a list.
- For an internal handler set up by internal_condition_case*,
- this can instead be the symbol t or `error'.
- t: handle all conditions.
- error: handle all conditions, and errors can run the debugger
- or display a backtrace. */
- Lisp_Object handler;
-
- Lisp_Object volatile var;
-
- /* Fsignal stores here the condition-case clause that applies,
- and Fcondition_case thus knows which clause to run. */
- Lisp_Object volatile chosen_clause;
-
- /* Used to effect the longjump out to the handler. */
- struct catchtag *tag;
-
- /* The next enclosing handler. */
- struct handler *next;
- };
-
-/* This structure helps implement the `catch' and `throw' control
- structure. A struct catchtag contains all the information needed
- to restore the state of the interpreter after a non-local jump.
-
- Handlers for error conditions (represented by `struct handler'
- structures) just point to a catch tag to do the cleanup required
- for their jumps.
-
- catchtag structures are chained together in the C calling stack;
- the `next' member points to the next outer catchtag.
+ handler structures are chained together in a doubly linked list; the `next'
+ member points to the next outer catchtag and the `nextfree' member points in
+ the other direction to the next inner element (which is typically the next
+ free element since we mostly use it on the deepest handler).