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Re: [sydjs] Functional Programming, Tail Recursion and Javascript

From:

Dmitry Baranovskiy

Date:

2010-12-01 @ 22:08

Hi James,

1. Nothing to support. There are six types in JavaScript: null, undefined,
number, string, boolean and object.
2. 4.  I wrote a bit about this here: 
http://dmitry.baranovskiy.com/post/typeof-and-friends
3. I am going to write a blog post about this, but in short

In JS there are objects and primitives. JS converts values from one type 
to other depending what you are doing with it:
	var a = "3";
	a--;
Here I applied decrement operator to string. It doesn’t make sense, but JS
convert it to number and then apply the operator. After second line a is a
number 2.
Another example:
	var a = "3";
	a.length
Strings are primitives, they don’t have properties. Dot operator, just 
like many others could only be applied to objects. When you trying to 
apply it to primitives JS converts them into objects and apply dot 
operator to those objects. So, second line is equivalent to:
	Object(a).length // or
	new String(a).length
Obviously assigning properties to primitives doesn’t work because every 
time you ask for property you are dealing with freshly created object.

4. typeof is much faster than anything else, besides it is the only way to
deal with non-existing variables:
	if (typeof blah == "undefined") …
Just beware that typeof lies in two cases:
	typeof null == "object" // should be "null"
	typeof function(){} == "function" // should be "object"

best,
Dmitry

On 01/12/2010, at 11:02 PM, freshtonic@gmail.com wrote:

> Hi Dmitry,
> 
> You're saying that you disagree but haven't supported your statements
> with an explanation. I'm genuinely interested :)
> 
> Cheers,
> 
> James.
> 
> On 1 December 2010 21:35, Dmitry Baranovskiy <dmitry@baranovskiy.com> wrote:
>> 1. Don’t believe that there nine types in JavaScript. There are six.
>> 2. “never use the == operator” is quite a lame statement.
>> 3. Boxed vs. unboxed chapter is all wrong
>> 4. “Don’t use typeof” is another questionable statement. I don’t like 
it either, but using constructor property is much worse.
>> 
>> Apart from that it’s useful read. Read it with caution. Question 
everything… including what I wrote here.
>> 
>> best,
>> Dmitry
>> 
>> 
>> On 01/12/2010, at 1:04 PM, Jared W wrote:
>> 
>>> To keep this discussion going, thought i would throw a link to the JS
>>> in 10 mins you briefly mentioned in your talk, i read it a week or so
>>> before the talk and was pleasantly surprised to see it raised. It is
>>> an awesome read for any one interested in Javascript, and some
>>> language theory link is here
>>> https://github.com/spencertipping/js-in-ten-minutes/
>>> 
>>> Also highly worth checking out his divergence library if you have a
>>> spare hour or so.
>>> 
>>> On Wed, Dec 1, 2010 at 10:49 AM, Jared W <Jared.Wyles@gmail.com> wrote:
>>>> I am sorry for that. :)
>>>> It was a pretty bad portion of the language. There is beauty in the
>>>> language i promise! I did preface the de-script-ion with 'please never
>>>> write code like this'. While it is possible to abuse the language to
>>>> such extremes, people should really think twice about doing it.
>>>> Also if that horrified you, never look at its typing system. Someone
>>>> with a love of functional languages would probably give up their
>>>> keyboard forever if you saw the abuse the type system allows.
>>>> 
>>>> Jared.
>>>> 
>>>> 
>>>> On Wed, Dec 1, 2010 at 10:43 AM, Erik de Castro Lopo
>>>> <mle+cl@mega-nerd.com> wrote:
>>>>> Daniel Bush wrote:
>>>>> 
>>>>>> Thinking out loud:
>>>>>> Am I the only one who thinks it's a small miracle that the browser got a
>>>>>> scripting language, much maligned early on, that ended up having lexical
>>>>>> scope and closures, higher order and anonymous functions and the ability to
>>>>>> create objects (via closures or the "new" keyword)?
>>>>> 
>>>>> I heard (but have never been able to confirm) that a very early version
>>>>> of Javascript was actually a cut-down version of scheme. When the author
>>>>> showed it to other people he was told "great idea, but no one is going to
>>>>> want to write scheme". He then changed the syntax to be more C and Java
>>>>> like.
>>>>> 
>>>>> Since you mentioned "much maligned" I must say, as some one who loves
>>>>> the real bondage and discipline languages like Ocaml and Haskell, what
>>>>> I saw in the Di-script-ions section of the last meeting really
>>>>> horrified me :-)
>>>>> 
>>>>> Erik
>>>>> --
>>>>> ----------------------------------------------------------------------
>>>>> Erik de Castro Lopo
>>>>> http://www.mega-nerd.com/
>>>>> 
>>>> 
>> 
>> 
> 
> 
> 
> -- 
> James