Please explain this error handler to me

I've been using this error handler in lisps where I modify system variables for a while now. I can't remember where I found this code below.

  (setq *error*
    (lambda (msg)
      (setvar "CMDECHO" CRcecho)
      (setvar "CLAYER" CRlayr)
      (setvar "ATTREQ" CRattreq)
      (princ msg)
      (princ)))

What's going here? I've read LEE Mac's tutorial where it's used as a function. Lee Mac seems to use a pretty different method for error hadling. How is setq being used to reset all the sysvar?

(setq *error* (lambda ( ... ) ... ) is merely an alternative to (defun *error* ( ... ) ... ) and just another way of assigning a function accepting a single argument to the *error* symbol.

As far I understand the *error* (handler) function works as a callback function, when the code crashes/errors out

and accepts only one argument - the error message ( msg symbol in that example ).

It took me quite a while to understand the callback functions (most oftenly used in Reactors and DCL (action_tile)).

So overall it looks like a pseudo-reactor... with a :vlr-LispWillError event.

As far I understand the *error* (handler) function works as a callback function, when the code crashes/errors out

and accepts only one argument - the error message ( msg symbol in that example ).

It took me quite a while to understand the callback functions (most oftenly used in Reactors and DCL (action_tile)).

 

So overall it looks like a pseudo-reactor... with a :vlr-LispWillError event.

I suppose I don't really understand callback functions. I'll read it up on it over the weekend. Thanks.