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Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 69 |
1 files changed, 69 insertions, 0 deletions
@@ -62576,6 +62576,75 @@ using the .code pprinl function. +.coNP Special variable @ *listener-greedy-eval-p* +.desc +The special variable +.code *listener-greedy-eval-p* +controls whether or not a "greedy evaluation" feature is enabled +in the listener. The default value is +.codn nil , +disabling the feature. + +Greedy evaluation means that after the listener evaluates an expression +successfully and prints its value, it then checks whether that value is +an expression that may be further subject to non-trivial evaluation. +If so, it evaluates that expression, and prints the resulting value. +The process is then repeated with the resulting value. It keeps repeating until +evaluation throws an error, or produces a self-evaluating object. + +These additional evaluations are performed in such a way that all warnings are +suppressed and all other exceptions are intercepted. + +Greedy evaluation doesn't affect the state of the listener. +Only the original expression is entered into the +history. Only the value of the original expression is saved in the result hash +or a numbered variable. The command line number +.code *n +is incremented by one. The additional evaluations are only performed for +the purpose of producing useful output. Of course, the evaluations may +have side effects. + +.TP* Example: + +.cblk + 1> (set *listener-greedy-eval-p* t) + t + 2> 'a + a + 3> (defvar b 2) + b + 2 + 4> (defvar c '(+ 2 2)) + c + (+ 2 2) + 4 + 5> (defvar d '(list '+ 2 2)) + d + (list '+ 2 2) + (+ 2 2) + 4 +.cble + +The +.code "(defvar d ...)" +form produces +.code d +symbol as its result value. That symbol has a variable binding as a result +of that +.code defvar +and so evaluates; that evaluation produces +.codn "(list '+ 2 2)" , +the contents of +.codn d . +That object is a Lisp expression and is evaluated, producing +.code "(+ 2 2)" +and that of course is also an expression, which reduces to +.codn 4 . +The object +.code 4 +is self-evaluating, and so the greedy evaluation process stops. + + .SH* SETUID/SETGID OPERATION On platforms with the Unix filesystem and process security model, \*(TX has |