(princ) function behavior

dallion · 发表于 2022-7-6 06:44:24

I have a simple error trap

(defun trap1 (errmsg)   (princ "\n An error has occured:\n")   (princ errmsg)   (setvar "blipmode" OLDBLIPMODE)   (setvar "osmode" OLDSNAP)   (setvar "LUnits" OLDLUNITS)   (setvar "LUPrec" OLDLUPREC)   (setvar "cmdecho" oldecho)   (setq *error* temperr)   (princ))

The (setq *error* temperr) line is supposed to return the error trap to the original function, stored in temperr. Besides being pretty useless, I noticed the (princ) call at the end was causing a bug - the original error trap was not restored.

I am wondering how exactly it happens that having the (princ) line causes this. It is my understanding that the last function evaluated is what is returned from a function, and that calling (princ) returns nil. But why doesn't the side effect of (setq *error* temperr) still happen?

Ahankhah · 发表于 2022-7-6 08:18:39

I guess the error is not for call to (princ). Should you test the following code?

copy

(defun trap1 (errmsg)(princ "\n An error has occured:\n")(princ errmsg)(if OLDBLIPMODE (setvar "blipmode" OLDBLIPMODE))(if OLDSNAP (setvar "osmode" OLDSNAP))(if OLDLUNITS (setvar "LUnits" OLDLUNITS))(if OLDLUPREC (setvar "LUPrec" OLDLUPREC))(if oldecho (setvar "cmdecho" oldecho))(setq *error* temperr)(princ))

[编程交流] (princ) function behavior

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