Macro

Summary

Allows source location to work when a form is copied by a macro.

Package

dspec

Signature

replacement-source-form original-form new-form => new-form-value

Arguments

original-form

A Lisp form.

new-form

A Lisp form.

Values

new-form-value

A Lisp object.

Description

A call to replacement-source-form can be used to allow the debugger and stepper to identify that original-form has been replaced by new-form in a macro expansion. Forms in a macro expansion that are eq to forms in the arguments to the macro will be identified automatically, but some macros (such as iterate) need to generate new forms that are equivalent to the original forms and wrapping them with replacement-source-form allows them to be identified too.

original-form should be a form that occurred in the arguments to the macro and does not otherwise occur in the expansion of the macro. new-form should be a form that was created by the macro.

The value of new-form, new-form-value, is returned when the replacement-source-form form is evaluated.

Examples

Without the dspec:replacement-source-form, the calls to pprint would be unknown to the debugger and stepper because the forms do not occur in the original source code:

(defmacro pprint-for-print (&body forms)

  `(progn

     ,@(loop for form in forms

             collect

             (if (and (consp form)

                      (eq (car form) 'print))

                 `(dspec:replacement-source-form

                   ,form

                   (pprint ,@(cdr form)))

               form))))