Major Section: IO
ACL2 output is generally printed in full. However, ACL2 can be directed to
abbreviate, or ``eviscerate'', objects before printing them, though the use
of a so-called ``evisc-tuple''. See evisc-tuple for a discussion of
evisc-tuples. The utility set-evisc-tuple modifies certain global
evisc-tuples, as explained below, to affect the extent to which ACL2
eviscerates objects during printing, for example during proof output or when
printing top-level evaluation results.
General Form:
(set-evisc-tuple evisc-tuple ; a legal evisc-tuple, or :DEFAULT
:iprint val ; one of *iprint-actions*
:sites sites ; either :ALL, or an element or a subset of the
; list (:TERM :LD :TRACE :ABBREV)
where the value of :iprint is passed to set-iprint, :sites :all
abbreviates :sites '(:TERM :LD :TRACE :ABBREV), and other documentation
is provided below. Note that all arguments are evaluated.See without-evisc for how to avoid evisceration for ACL2 output.
The following example illustrates an invocation of set-evisc-tuple that
limits the print-level to 3 -- only three descents into list structures are
permitted before eviscerating a subterm -- and limits the print-length to 4
-- only the first four elements of any list structure will be printed.
ACL2 !>(set-evisc-tuple (evisc-tuple 3 ; print-level
4 ; print-length
nil ; alist
nil ; hiding-cars
)
:iprint :same ; better yet, T
:sites :all)
(:TERM :LD :TRACE :ABBREV)
ACL2 !>'((a b ((c d)) e f g) u v w x y)
((A B (#) E ...) U V W ...)
ACL2 !>
We recommend however using :iprint t so that eviscerated terms may be
read back in; see set-iprint. Indeed, the :iprint argument is required
as a reminder to the user to consider that issue, unless iprinting has been
enabled at least once. If :sites or a required :iprint argument is
omitted, however, ACL2 will query the user for the missing arguments rather
than causing an error.ACL2 eviscerates by default only in a few cases, primarily in informational
messages for errors, warnings, and queries (i.e., in the :EVISC case
below). Users can modify the default behavior by supplying a suitable
argument to set-evisc-tuple. The argument may be :default, which
denotes the evisceration provided when ACL2 starts up. Otherwise that
argument is an evisc-tuple, which is either nil (no evisceration) or as
described above. Moreover, there are four evisc-tuple ``evisceration
contexts'', each with its own evisceration control. The value returned by
set-evisc-tuple indicates the evisceration contexts whose evisc-tuple has
been set. The evisceration contexts are as follows, all of which use a
default value of nil for the hiding-cars. Accessors are also shown for
retrieving the corresponding evisc-tuple.
o
:TERM-- used for printing terms. The accessor is(term-evisc-tuple flg state), whereflgis ignored ifset-evisc-tuplehas been called for:termwith value other than:default, and otherwise (hence initially): aflgofnilindicates an evisc-tuple ofnil, and otherwise the term-evisc-tuple has a print-level of 3 and print-length of 4.o
:ABBREV-- used for printing informational messages for errors, warnings, and queries. Initially, the alist abbreviates the ACL2world, print-level is 5, and print-level is 7. The accessor is(abbrev-evisc-tuple state).o
:GAG-MODE-- used for printing induction schemes (and perhaps, in the future, for other printing) when gag-mode is on. If gag-mode is off, the value used for this evisc-tuple is(term-evisc-tuple nil state). But if gag-mode is on (i.e.,(gag-mode)evaluates to a non-nilvalue), then with one exception, the value is an evisc-tuple ornil, to be used in gag-mode for printing of induction schemes and, during proofs, the ``The non-trivial part of the guard conjecture''. The exceptional value ist, which indicates that in gag-mode, no printing of induction schemes should be and the guard conjecture should be printed using(term-evisc-tuple t state). The accessor is(gag-mode-evisc-tuple state).o
:LD-- used by the ACL2 read-eval-print loop. The accessor is(ld-evisc-tuplestate).o
:TRACE-- used for printing trace output. No accessor is available (though in raw Lisp,(trace-evisc-tuple)returns the trace-evisc-tuple).
Each context ectx also has an updater,
(set-ectx-evisc-tuple val state), where val is a legal value for
set-evisc-tuple as described above: :default or an evisc-tuple
(possibly nil).
Note that the break-rewrite commands and the proof-checker generally do their printing using the term-evisc-tuple.