handler's continuation is otherwise unspecified."
(throw throw-key obj))
-(define-macro (guard var+clauses . body)
- "Syntax: (guard (<var> <clause1> <clause2> ...) <body>)
+(define-syntax guard
+ (syntax-rules (else)
+ "Syntax: (guard (<var> <clause1> <clause2> ...) <body>)
Each <clause> should have the same form as a `cond' clause.
Semantics: Evaluating a guard form evaluates <body> with an exception
clause, then raise is re-invoked on the raised object within the
dynamic environment of the original call to raise except that the
current exception handler is that of the guard expression."
- (let ((var (car var+clauses))
- (clauses (cdr var+clauses)))
- `(catch ',throw-key
- (lambda ()
- ,@body)
- (lambda (key ,var)
- (cond ,@(if (eq? (caar (last-pair clauses)) 'else)
- clauses
- (append clauses
- `((else (throw key ,var))))))))))
+ ((guard (var clause ... (else e e* ...)) body body* ...)
+ (catch throw-key
+ (lambda () body body* ...)
+ (lambda (key var)
+ (cond clause ...
+ (else e e* ...)))))
+ ((guard (var clause clause* ...) body body* ...)
+ (catch throw-key
+ (lambda () body body* ...)
+ (lambda (key var)
+ (cond clause clause* ...
+ (else (throw key var))))))))
+
;;; (srfi srfi-34) ends here.
HCoop / bpt / guile.git / commitdiff