CW-GSTACK.html -- ACL2 Version 6.3

## CW-GSTACK

debug a rewriting loop or stack overflow

    Major Section:  OTHER

    Example Forms:
    (cw-gstack)
    (cw-gstack :frames 10)       ; show only the top 10 frames
    (cw-gstack :frames '(1 10))  ; same as above:  show only frames 1 through 10
    (cw-gstack :frames '(10 20)) ; show only frames 10 through 20
    (cw-gstack :evisc-tuple (evisc-tuple 3 4 nil nil))
                                 ; print with print-level 3 and print-length 4
    (cw-gstack :evisc-tuple nil) ; print using default ``evisceration'',
                                 ;   essentially the same as just above
    (cw-gstack :evisc-tuple '(nil 3 4 (hide)))
                                 ; same as just above

    General Form:
    (cw-gstack :frames frames :evisc-tuple evisc-tuple)

where `:frames` and `:evisc-tuple` are optional, but if they are supplied, their values are evaluated. The value of `frames` should be either a natural number or a list of two natural numbers, the first less than the second; and the value of `evisc-tuple` should be an evisc-tuple (see evisc-tuple). If `:evisc-tuple` is omitted, then substructures deeper than 3 are replaced by ```#`'' and those longer than 4 are replaced by ```...`'', and terms of the form `(hide ...)` are printed as `<hidden>`. Also see set-iprint for an alternative to printing ```#`'' and ```...`''.

Stack overflows may occur, perhaps caused by looping rewrite rules. In some Lisps, stack overflows may manifest themselves as segmentation faults, causing the entire ACL2 image to crash. Finding looping rewrite rules can be tricky, especially if you are using books supplied by other people. (However, see set-rewrite-stack-limit for a way to avoid stack overflows caused by rewriter loops.)

Normally, a stack overflow will cause the printing of an error message that suggests how to proceed. Just follow those instructions, and you will generally be able to see what is causing the loop.

Suggestion: Once you have found the loop and fixed it, you should execute the ACL2 command `:``brr` `nil`, so that you don't slow down subsequent proof attempts.