[REBOL] Re: Binding problem with 'do
From: lmecir::mbox::vol::cz at: 1-Aug-2005 12:27
Ladislav Mecir napsal(a):
>I think, that it is necessary to articulate the "rule of thumb"
>regarding string execution:
>
>*Do not transform Rebol code to string, if you are going to evaluate it*.
>
>Let's have a look at the original code:
>
> code: load rejoin["append output do-" type " name layout"]
> ?? code ;; see code "dump" below
> do code
>
>So, what is wrong about it? The wrong part is, that there is a
>transformation of legal Rebol code [append output do-type name layout]
>to string and back again, while the only thing that had to be
>transformed was the do-type part and it had to be transformed *from*
>string, i.e. in the opposite direction.
>
>Is that understandable enough for less experienced readers?
>
>-L
>
Appendix: the code above is a wrong way, so what is the "right
beginner's way" of doing things in this case?
Here is the simplest way I came to:
; transform the type string to a word and get the value of it
do-type: get to word! join "do-" type
; evaluate the code
append output do-type name layout
*Warning! because the do-type "translation" uses TO WORD!, the word
created this way will be global, while the original intention of the
programmer might have been to use e.g. 'do-checkbox word, which was
meant to be local.*
How to make the code more "bulletproof", i.e. not being "caught" by the
fact, that TO WORD! creates globals? Here is an improvement:
; transform the type string to a do-... word in the same context as
the 'do-radio word is and get its value
do-type: get bind to word! join "do-" type 'do-radio
; evaluate the code
append output do-type name layout
Hope it will be of some use.
-Ladislav
