Selecting Guile Pretty-Printers (Debugging with GDB)
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23.4.3.9 Selecting Guile Pretty-Printers
There are three sets of pretty-printers that GDB searches:
- Per-objfile list of pretty-printers (see Objfiles In Guile).
- Per-progspace list of pretty-printers (see Progspaces In Guile).
- The global list of pretty-printers (see Guile Pretty Printing API). These printers are available when debugging any inferior.
Pretty-printer lookup is done by passing the value to be printed to the lookup function of each enabled object in turn. Lookup stops when a lookup function returns a non-#f
value or when the list is exhausted. Lookup functions must return either a <gdb:pretty-printer-worker>
object or #f
. Otherwise an exception is thrown.
GDB first checks the result of objfile-pretty-printers
of each <gdb:objfile>
in the current program space and iteratively calls each enabled lookup function in the list for that <gdb:objfile>
until a non-#f
object is returned. If no pretty-printer is found in the objfile lists, GDB then searches the result of progspace-pretty-printers
of the current program space, calling each enabled function until a non-#f
object is returned. After these lists have been exhausted, it tries the global pretty-printers list, obtained with pretty-printers
, again calling each enabled function until a non-#f
object is returned.
The order in which the objfiles are searched is not specified. For a given list, functions are always invoked from the head of the list, and iterated over sequentially until the end of the list, or a <gdb:pretty-printer-worker>
object is returned.
For various reasons a pretty-printer may not work. For example, the underlying data structure may have changed and the pretty-printer is out of date.
The consequences of a broken pretty-printer are severe enough that GDB provides support for enabling and disabling individual printers. For example, if print frame-arguments
is on, a backtrace can become highly illegible if any argument is printed with a broken printer.
Pretty-printers are enabled and disabled from Scheme by calling set-pretty-printer-enabled!
. See Guile Pretty Printing API.
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