7.6.2.12 rnrs exceptions

The (rnrs exceptions (6)) library provides functionality related to signaling and handling exceptional situations. This functionality re-exports Guile’s core exception-handling primitives. See Exceptions, for a full discussion. See SRFI-34, for a similar pre-R6RS facility. In Guile, SRFI-34, SRFI-35, and R6RS exception handling are all built on the same core facilities, and so are interoperable.

Scheme Procedure: with-exception-handler handler thunk

See Raising and Handling Exceptions, for more information on with-exception-handler.

Scheme Syntax: guard (variable clause1 clause2 ...) body

Evaluates the expression given by body, first creating an ad hoc exception handler that binds a raised exception to variable and then evaluates the specified clauses as if they were part of a cond expression, with the value of the first matching clause becoming the value of the guard expression (see Conditionals). If none of the clause’s test expressions evaluates to #t, the exception is re-raised, with the exception handler that was current before the evaluation of the guard form.

For example, the expression

(guard (ex ((eq? ex 'foo) 'bar) ((eq? ex 'bar) 'baz)) 
  (raise 'bar))

evaluates to baz.

Scheme Procedure: raise obj

Equivalent to core Guile (raise-exception obj). See Raising and Handling Exceptions. (Unfortunately, raise is already bound to a different function in core Guile. See Signals.)

Scheme Procedure: raise-continuable obj

Equivalent to core Guile (raise-exception obj #:continuable? #t). See Raising and Handling Exceptions.