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8.2.2 Hook functions

Hooks are functions evaluated before or after executing a mixvm command (or its corresponding Scheme function wrapper), or after an explicit or conditional breakpoint is found during the execution of a MIX program. The following functions let you install hooks:

Function: mix-add-pre-hook command hook

Adds a function to the list of pre-hooks associated with the given command. command is a string naming the corresponding mixvm command, and hook is a function which takes a single argument: a string list of the commands arguments. The following scheme code defines a simple hook and associates it with the run command:

(define run-hook
  (lambda (args)
    (display "argument list: ")
    (display args)
(mix-add-pre-hook "run" run-hook)

Pre-hooks are executed, in the order they are added, before invoking the corresponding command (or its associated Scheme wrapper function).

Function: mix-add-post-hook command hook

Adds a function to the list of pre-hooks associated with the given command. The arguments have the same meaning as in mix-add-pre-hook.

Function: mix-add-global-pre-hook hook
Function: mix-add-global-post-hook hook

Global pre/post hooks are executed before/after any mixvm command or function wrapper invocation. In this case, hook takes two arguments: a string with the name of the command being invoked, and a string list with its arguments.

Function: mix-add-break-hook hook
Function: mix-add-cond-break hook

Add a hook funtion to be executed when an explicit (resp. conditional) breakpoint is encountered during program execution. hook is a function taking two arguments: the source line number where the hook has occurred, and the current program counter value. The following code shows a simple definition and installation of a break hook:

(define break-hook
  (lambda (line address)
    (display "Breakpoint at line ") (display line)
    (display " and address ") (display address)
(mix-add-break-hook break-hook)

Break hook functions are entirely implemented in Scheme using regular post-hooks for the next and run commands. If you are curious, you can check the Scheme source code at prefix/share/mdk/mixguile-vm-stat.scm (where prefix stands for your root install directory, usually /usr or /usr/local.

See Hook functions for further examples on using hook functions.

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