18.2.11 Printing in Edebug

If an expression in your program produces a value containing circular list structure, you may get an error when Edebug attempts to print it.

One way to cope with circular structure is to set print-length or print-level to truncate the printing. Edebug does this for you; it binds print-length and print-level to the values of the variables edebug-print-length and edebug-print-level (so long as they have non-nil values). See Output Variables.

user option edebug-print-length

If non-nil, Edebug binds print-length to this value while printing results. The default value is 50.

user option edebug-print-level

If non-nil, Edebug binds print-level to this value while printing results. The default value is 50.

You can also print circular structures and structures that share elements more informatively by binding print-circle to a non-nil value.

Here is an example of code that creates a circular structure:

(setq a (list 'x 'y))
(setcar a a)

Custom printing prints this as ‘Result: #1=(#1# y)’. The ‘#1=’ notation labels the structure that follows it with the label ‘1’, and the ‘#1#’ notation references the previously labeled structure. This notation is used for any shared elements of lists or vectors.

user option edebug-print-circle

If non-nil, Edebug binds print-circle to this value while printing results. The default value is t.

Other programs can also use custom printing; see cust-print.el for details.