Re: grammar triviality with '&&'

[Vincent Lefevre <vincent@xxxxxxxxxx>]

On 2015-03-02 00:54:40 -0800, Bart Schaefer wrote:
> On Mar 2,  3:27am, Vincent Lefevre wrote:
> }
> } However "&& [ -e file2 ]" could constitute a list too. There is
> } currently a parse error, but zsh could have an extension to accept
> } it as being equivalent to: "[[ $? -eq 0 ]] && [ -e file2 ]". Would
> } there be anything wrong with such an extension?
> 
> If nothing else, the errexit option would fail.  With errexit,
> 
>     false
>     || anything
> 
> would never get beyond "false", whereas
> 
>     false || anything
> 
> proceeds at least through "anything".

I agree that's not equivalent, but this would not be a problem
in a "if ... then" construct (though I think it's a bad idea
to use such a feature here).

> You also get strange crap like
> 
>     while && this; do || if && that; then || thus; fi; done
> 
> which would mean what, exactly?

while [[ $? -eq 0 ]] && this; do [[ $? -ne 0 ]] || if [[ $? -eq 0 ]] && that; then [[ $? -ne 0 ]] || thus; fi; done

> Finally if it's OK to have nothing before && / ||, then it would also be
> syntactically OK to write
> 
>     && || && || && && ...

I disagree. Only a && or || as the first word of a list would have
a special meaning.

-- 
Vincent Lefèvre <vincent@xxxxxxxxxx> - Web: <https://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)