On 14-Apr-06, at 6:53 AM, Joo ChurlSoo wrote:

> When `#!key' does not appear in the <extended formals> and there is
> no <rest
> formal>, an error is signaled regardless of presence of `#!
> optional' if there
> are any remaining actual arguments.  But When `#!key' appears in
> the <extended
> formals> regardless of presence of <rest formal>, an error is not
> signaled in
> spite of superfluous actual arguments.  What is its rationale?

[Correction: the spec uses "it is an error", not "an error is
signaled".]

This behaviour, which is from DSSSL, allows the called procedure to
accept other named parameters than the ones appearing in the formal
parameter list.  Note that in this case the rest parameter will
contain the list of all named parameters (including those that do not
appear in the formal parameter list).  So the called procedure can
parse these explicitly or pass them on to other procedures using an
"apply".  This can be useful to modularize the handling of the named
parameters in procedural layers.  Each layer picks the parameter(s)
that it knows how to handle out of the parameter list, and passes the
parameter list to the next layer.  This way a layer does not need to
know what the previous or next layer handles.

Marc