diff options
| -rw-r--r-- | txr.1 | 28 |
1 files changed, 19 insertions, 9 deletions
@@ -42375,21 +42375,26 @@ mode. Exception processing mode terminates in one of several ways: A .I catch is found which matches the exception, and control is transferred -to the catch. Catches are defined by the +to the catch by a non-local transfer which performs unwinding. Catches are +defined by the .code catch macro. .IP - -A handler accepts the exception by performing a non-local transfer. +A +.I handler +is found which matches the exception, and control is transferred to +the handler by invoking its function. The handler function accepts the +exception by performing a non-local transfer to a destination of its choice, or +else declines to accept the exception by returning. Handlers are defined by the .code handler-bind operator or .code handle -macro. If a handler returns, then by so doing it declines to -handle the exception. +macro. .IP - If no catch or accepting handler is found for an exception derived from .code error -exception and +and .code *unhandled-hook* is .codn nil , @@ -42444,10 +42449,15 @@ or else declines the exception by performing an ordinary return. Catches and handlers are identified by exception type symbols. A catch or handler is eligible to process an exception if it handles a type which is a supertype of the exception which is being processed. Handles and catches -are located in a combined search which proceeds from the innermost nesting -to the outermost. When an eligible handle is encountered, it is called. If -it returns, the search continues. When an eligible catch is encountered, -the search stops and a control transfer takes place to the catch site. +are found by means of a combined search which proceeds from the innermost +nesting of dynamic scope to the outermost, without performing any unwinding. +When an eligible handler is encountered, its registered function is called, thereby suspending the +search. If the handler function returns, the search continues from that scope +to yet unvisited outer scopes. When an eligible catch is encountered rather +than a handler, the search terminates and a control transfer takes place to the +catch site. That control transfer then performs unwinding, which requires it to +make a second pass through the same nestings of dynamic scope that had just +been traversed in order to find that catch. .NP* Handlers and Sandboxing |