PUSH-UNTOUCHABLE.html -- ACL2 Version 6.3

## PUSH-UNTOUCHABLE

add name or list of names to the list of untouchable symbols

    Major Section:  SWITCHES-PARAMETERS-AND-MODES

    Examples:
    (push-untouchable my-var nil)
    (push-untouchable set-mem t)

    General Form:
    (push-untouchable name{s}  fn-p :doc doc-string)

where `name{s}` is a non-`nil` symbol or a non-`nil` true list of symbols, `fn-p` is any value (but generally `nil` or `t`), and `doc-string` is an optional documentation string not beginning with ```:Doc-Section` ...''. If `name{s}` is a symbol it is treated as the singleton list containing that symbol. The effect of this event is to union the given symbols into the list of ``untouchable variables'' in the current world if `fn-p` is `nil`, else to union the symbols into the list of ``untouchable functions''. This event is redundant if every symbol listed is already a member of the appropriate untouchables list (variables or functions).

When a symbol is on the untouchables list it is syntactically illegal for any event to call a function or macro of that name, if `fn-p` is non-`nil`, or to change the value of a state global variable of that name, if `fn-p` is `nil`. Thus, the effect of pushing a function symbol, `name`, onto untouchables is to prevent any future event from using that symbol as a function or macro, or as a state global variable (according to `fn-p`). This is generally done to ``fence off'' some primitive function symbol from ``users'' after the developer has used the symbol freely in the development of some higher level mechanism.

Also see remove-untouchable.