3.5.8 Multiple return values

A Scheme expression can evaluate to an arbitrary finite number of values. These values are passed to the expression’s continuation.

Not all continuations accept any number of values. For example, a continuation that accepts the argument to a procedure call is guaranteed to accept exactly one value. The effect of passing some other number of values to such a continuation is unspecified. The call-with-values procedure makes it possible to create continuations that accept specified numbers of return values. If the number of return values passed to a continuation created by a call to call-with-values is not accepted by its consumer that was passed in that call, then an exception is raised. A more complete description of the number of values accepted by different continuations and the consequences of passing an unexpected number of values is given in the description of the values procedure.

A number of forms in the base library have sequences of expressions as subforms that are evaluated sequentially, with the return values of all but the last expression being discarded. The continuations discarding these values accept any number of values.