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elisp: Printing in Edebug

 
 17.2.11 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).  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 '(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.
 

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