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Subject: Re: [9front] Bug in rc
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Quoth Yury Chumak <sfynkx@gmail.com>:
> Hello all..
> 
> Noticed that rc returns error 'stack overflow' if code consists
> 'switch' construction with big amount of 'case' blocks. Steps to
> reproduce:
> 
> 1.Generate test script by next code:
> #!/bin/rc
> echo '#!/bin/rc' >test.rc
> echo 'switch($*){' >>test.rc
> for(i in `{seq 1 250}){
>     echo ' case ' $i>>test.rc
>     echo '    echo number ' $i>>test.rc
> }
> echo ' case *' >>test.rc
> echo '    echo number none'>>test.rc
> echo '}'>>test.rc
> 
> 2. Run result script:
> % chmod +x test.rc
> % test.rc
> ./test.rc:497: token 248: yacc stack overflow
> 
> The 'switch' construction works normaly with number 'case' block less than 247.
> In comparison linux's bash has no limitation to number elements in
> 'case' block (at least 500k tested).
> 

Yes, the grammar for this is right recursive,
which means the full stack is collected before
it's reduced:

	body:	cmd
	|	cmdsan body		{$$=tree2(';', $1, $2);}

You can play around with refactoring it to be
left recursive, or maybe bringing in the C rewrite
of the parser from plan9port (ideally with tests).

But I'm not sure why it matters; you can hit a
limit with a huge switch, but it doesn't seem
like a limit for practical code.