On Tue, Mar 9, 2010 at 6:26 AM, Srini <[email protected]> wrote:
> Hi. I am completely new to clojure - my 3rd day or so. Need to go buy
> a book on the subject. So please help me with a couple of things:
>
> Item 1) I have two calls to count. One works, and the other does not.
>
> ; counts number of items in collection
> user=> (count (list 1 2 3 4 "er" 34) )
> 6
>
> ; count does not work. I get an exception. Need to figure out what I
> am doing wrong here.
> user=> (count (list 23 "3er" oel" 5) )
> java.lang.Exception: EOF while reading string
You are missing a double-quotation character before eol"
>
> Item 2) I see from the documentation that the contains? function (it
> is a function, right? just want to be sure. this is my 2nd or 3rd day
> learning about clojure.) returns true if key is present in collection.
> And there is a reference in the online docs to "numerically indexed
> collections like vectors and Java arrays". In the following examples,
> the first one works as I expected. But the second one does not work as
> I thought. How do I check if an item is in a list?
>
> ; does the vector contain index 0?
> user=> (contains? [1 2 3 4] 0)
> true
>
> ; could not get it to work for lists. apparently works only for
> numerically indexed collections like vectors.
> ; doesn't throw an exception either. "intuitively", I think the
> following should have returned true.
> user=> (contains? (list "3e" "2 tired" "1 more") "3e" )
> false
I think contains? only work on things that are associative:
user=> (associative? [])
true
user=> (associative? (list))
false
So a list is not associative, as it has no (near) constant-time way of
looking up things in it by index, key or value.
Maybe you want to use a set instead of a list:
user=> (contains? #{"3e" "2 tired" "1 more"} "3e" )
true
>
> Your help is much appreciated.
>
> Thank you for your time. - Srini
> As an aside, I guess I am approaching this as I have regular
> procedural languages like C, C++, Java, C#, VB, and my all-time
> favourite so far - Python, etc. And its taking a different kind of
> thinking to even understand the basics of closure since its just so
> different from the others. I am recording my learning experiences in
> my very first blog ever :) http://closurefp.blogspot.com/ Hopefully it
> will help someone.
>
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--
Venlig hilsen / Kind regards,
Christian Vest Hansen.
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