guard

(guard (variable clause...) body...)

Evaluates body and answers the value of its last expression. If the body raises an object -- through raise, raise-continuable or error, or as an error a built-in procedure signals -- the body is left (the after thunks of the dynamic-winds inside it run), variable is bound to the object, and the clauses are tried as in cond, => and else included. When no clause is taken, the object is raised again from the guard.

Deviations:

• The object is raised again after the body has been left, so a with-exception-handler outside the guard cannot resume a raise-continuable of the body: its handler returning is a secondary error. Gauche resumes the body.
• A body answering several values answers its first one.
• On WebAssembly a string index out of range is not checked: string-ref past the end answers a character instead of raising. error, raise, an arithmetic type error, car of a non-pair and a vector index out of range are caught on every backend.
• eval refuses guard by name.