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Top-level

Evaluate a top-level form as a function body

Some forms, such as calls of with-local-stobj, are illegal when supplied directly to the ACL2 top-level loop. The macro top-level provides a workaround in such cases, by defining a temporary :program-mode function named top-level-fn whose only argument is state and whose body is the form to be evaluated. When the call of top-level returns there is no change to the existing ACL2 logical world. The following edited log illustrates all of the above points.

ACL2 !>:pbt 0
          0  (EXIT-BOOT-STRAP-MODE)
ACL2 !>(defstobj st fld)

Summary
Form:  ( DEFSTOBJ ST ...)
Rules: NIL
Time:  0.01 seconds (prove: 0.00, print: 0.00, other: 0.01)
 ST
ACL2 !>(top-level
        (with-local-stobj
         st
         (mv-let (result st)
                 (let ((st (update-fld 17 st)))
                   (mv (fld st) st))
                 result)))
17
ACL2 !>(top-level
        (with-local-stobj
         st
         (mv-let (result st)
                 (let ((st (update-fld 17 st)))
                   (mv (fld st) st))
                 (mv nil result state))))
 17
ACL2 !>(top-level
        (with-local-stobj
         st
         (mv-let (result st)
                 (let ((st (update-fld 17 st)))
                   (mv (fld st) st))
                 (mv result state))))
(17 <state>)
ACL2 !>:pbt 0
          0  (EXIT-BOOT-STRAP-MODE)
   d      1:x(DEFSTOBJ ST FLD)
ACL2 !>

Each argument of top-level after the first should be a declare form or documentation string, as the list of these extra arguments will be placed before the first argument when forming the definition of top-level-fn.

Top-level generates a call of ld, so that the value returned is printed in the normal way. The call of top-level itself actually evaluates to (mv erp :invisible state), where erp is t if and only evaluation of the call of top-level-fn caused an error, which normally results in no additional output. (For details about ``caused an error'', see the definition of top-level in the ACL2 source code, and see ld-error-action.)

Since the defined function top-level takes only state as a parameter, the given form should not include any user-defined stobjs that occur free in the form.

Finally, note that since top-level runs a function that is defined in :program mode, it is possible for a raw lisp error to occur. Here is an example.

ACL2 !>(top-level (car 3))

***********************************************
************ ABORTING from raw Lisp ***********
********** (see :DOC raw-lisp-error) **********
Error:  The value 3 is not of the expected type LIST.
While executing: CAR
***********************************************