Rebol PARSE rule to match to first occurrence of at least 2 #[none]s

问题

See similar question for string case.

In R3-Alpha, I tried to adapt the @sqlab response to block case:

parse [x x x x #[none] a #[none] #[none] b] [to [none! none!] ??]

I expect ??: [#[none] #[none] b], but get

** Script error: PARSE - invalid rule or usage of rule: none!

It's the result right and my expectation wrong? Or it's a bug?

回答1:

I can just show a solution for Red and Rebol2. As the words in the rule are reduced automatic, you have to shield them.

Red

>> parse [x x x x _ a _ _ b] [to [ '_ '_] y: ]
== false
>> 
>> y
== [_ _ b]

Rebol2

>> parse [x x x x _ a _ _ b] [some [r: [ '_ '_  ] (y: r) | skip]   ]
== true
>> y
== [_ _ b]

After the editing of the question by HostileFork the solution for Red looks like that

>> parse [x x x x #[none] a #[none] #[none] b] [to [none! none!] y:] 
== false
>> y
== [none none b]
>> 

example according the question in the comment of giuliolunati

>> parse  [x x x x 0 a 1 2 b]  [to [integer! integer!] y:]
== false
>> y
== [1 2 b]

来源：https://stackoverflow.com/questions/54577826/rebol-parse-rule-to-match-to-first-occurrence-of-at-least-2-nones