On Oct 6, 2008, at 9:07 AM, hotcore wrote:
> I was playing around with data structures and found that I couldn't
> type:
> (conj #{aap noot mies} 'wim)
> which results in:
> java.lang.Exception: Unable to resolve symbol: mies in this context
>
> Instead I have to type:
> (conj '#{aap noot mies} 'wim)
> or:
> (conj (set '(aap noot mies)) 'wim)
>
> I wonder why the quote is needed. Normally the quote is only used to
> prevent the first item of a list being interpreted as a (special)
> operator / function; but that's not the case here. Or is it?
In addition to literal lists, symbols also evaluate to something other
than themselves. Without a quote:
- a list evaluates to the result of a function call
- a symbol is first "resolved" to identify a let-bound name or a var
that it represents and evaluates to the value bound to that name or var.
The error message you got is describing the latter case.
The line you typed:
> (conj #{aap noot mies} 'wim)
is not meaningless--it just isn't the correct way to express what you
wanted.
Here's a context where it would have been accepted:
user=> (let [aap 1 noot 2 mies 3]
(conj #{aap noot mies} 'wim))
#{1 2 3 wim}
user=>
In addition to these:
> Instead I have to type:
> (conj '#{aap noot mies} 'wim)
> or:
> (conj (set '(aap noot mies)) 'wim)
You could have also typed:
(conj #{'aap 'noot 'mies} 'wim)
Which makes it clear that it's symbol evaluation that you're
suppressing with the quotes.
--Steve
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