set-pprint-dispatch
set-pprint-dispatch type-specifier function &optional priority table → nil
type-specifier—a type specifier. This is now a valid type specifier! -kmp 30-Apr-91 or a list of the form \f{(cons \param{type-specifier} \param{type-specifier})} or {\tt (cons \param{type-specifier})}. \editornote{KMP: Can the type-specifier in a cons specifier also be a usage of CONS? Why don't we extend the CONS type specifier rather than make this special case?}
function—a function, a function name, or nil.
priority—a real. The default is 0.
table—a pprint dispatch table. The default is the value of *print-pprint-dispatch*.
Installs an entry into the pprint dispatch table which is table.
Type-specifier already said above. -kmp
must be a valid \term{type specifier} andis the key of the entry. The first action of set-pprint-dispatch is to remove any pre-existing entry associated with type-specifier. This guarantees that there will never be two entries associated with the same type specifier in a given pprint dispatch table. Equality of type specifiers is tested by equal.
Two values are associated with each type specifier in a pprint dispatch table: a function and a priority. The function must accept two arguments: the stream to which output is sent and the object to be printed. The function should pretty print the object to the stream. The function can assume that object satisfies the type given by type-specifier. The function must obey *print-readably*. (see issue DATA-IO)Any values returned by the function are ignored.
Priority is a priority to resolve conflicts when an object matches more than one entry.
It is permissible for function to be nil. In this situation, there will be no type-specifier entry in table after set-pprint-dispatch returns.
None.
None.
None.
An error is signaled if priority is not a real.
None.
Since pprint dispatch tables are often used to control the pretty printing of Lisp code, it is common for the type-specifier to be an expression of the form
(cons car-type cdr-type)
This signifies that the corresponding object must be a cons cell whose car matches the type specifier car-type and whose cdr matches the type specifier cdr-type. The cdr-type can be omitted in which case it defaults to t.
I don't think this note had any content. -kmp 13-Jan-91 ---------------------------------------------------------------------- Implementation note: The restriction above is very useful to users without actually limiting what Common Lisp implementors can do. It is possible for implementors to set up any kind of pretty printing they desire using the range of priorities available to them. ----------------------------------------------------------------------