Hi Ryan,
Ryan Cole wrote:
<...>
> So one difference is probe evaluates its argument, whereas
> ?? captures the argument without evaluation and attempts to
> print its word along with its value. The little tick mark does in
> ??'s function spec grabs a value without evaluating it like normal.
>
> A common example...
>
>
>>>?? b: 5
>>
> b:
> == 5
>
>>>probe b: 5
>>
> 5
> == 5
>
>
> As you see ?? printed out the set-word! b: and returned 5, where
> probe printed 5 and returned 5. This suprise result that happens with
> ?? occurs becuase it the set-word b action does not happen until after ??
> has returned its value--which is the set-word b.
This discription is a little bit misleading: in the case of '?? b: is
printed, but 5 isn't returned by '??, 5 is returned because it didn't
get eaten, and was the last value on the line, as can be seen in this
extended example.
>> b
** Script Error: b has no value
** Near: b
>> ?? b: 7
b:
== 7
>> b
** Script Error: b has no value
** Near: b
>> probe b: 7
7
== 7
>> b
== 7
>> ?? b:
b:
== b:
>> ?? b
b: 7
== 7
So,
'probe can be used to print the value of _any_ expression,
'?? normally only makes sense with words, but you get the added
benefit of being told the name of the word.
Kind regards,
Ingo
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