why is eval needed?

[Ray Andrews <rayandrews@eastlink.ca>]

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  In a script:

    local level='-L 2'
    tree $level
    #eval tree $level

run it:

     2 /aWorking/Zsh/Source/Wk 0 $ . testing
     tree: Missing argument to -L option.

If I use 'eval' it's fine.  Now, I roughly understand that we need 
'eval' when there's some complicated nesting of expansions or some other 
complexity, but I also recall that in almost every case where I've 
discussed an 'eval' here, I've been shown that it isn't really needed.  
In this case the expansion seems so trivial that I'm puzzled.  If 
'level' were some other switch that didn't require a space in it ('tree' 
demands a space between the 'L' and the number) then it works without 
eval, but what's the issue?  The '2' is there, why does 'tree' not see 
it?  Is this one of those invisible bogeys?  Something about argument 
counts or such?  But quoting didn't change the error message.



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