February 10, 2012
On Friday, February 10, 2012 13:32:56 Marco Leise wrote:
> I know that feeling. I had no exposure to functional programming and options like chain never come to my head. Although "map" is a concept that I made friends with early.

It would benefit your programming in general to learn a functional programming language and become reasonably proficient in it, even if you don't intend to program in it normally. It'll increase the number of tools in your programming toolbox and improve your programming in other programming languages. It's something that not enough programmers get sufficient exposure to IMHO.

- Jonathan M Davis
February 13, 2012
On 11 February 2012 10:45, Jonathan M Davis <jmdavisProg@gmx.com> wrote:
> On Friday, February 10, 2012 13:32:56 Marco Leise wrote:
>> I know that feeling. I had no exposure to functional programming and options like chain never come to my head. Although "map" is a concept that I made friends with early.
>
> It would benefit your programming in general to learn a functional programming language and become reasonably proficient in it, even if you don't intend to program in it normally. It'll increase the number of tools in your programming toolbox and improve your programming in other programming languages. It's something that not enough programmers get sufficient exposure to IMHO.
>
> - Jonathan M Davis

I found that learning Haskell made me significantly better at what I do. New paradigms are good for reminding you to think outside the box, I also learnt Prolog for a university course (AI) and that was an interesting challenge. Logical programming, where you define the boundaries of the program and then it works out the possible answers for you, amazingly useful for BNF grammars and similar constructs.

If fact it's got to the point where I feel hamstrung if I can't do at least function passing (fortunately C, C++ and D can do this), and I prefer to work with languages that support closures and anonymous functions, since you can do wonders with simple constructs like map, fold (reduce) and filter. In fact a naive implementation of quicksort can be done succinctly in any language that supports filter.

    T[] sort(T)(T[] array) {
        pivot = array[array.length/2];
        return sort(filter!("a < "~pivot)(array)~pivot~sort(filter!("a
> "~pivot)(array));
    }

(Disclaimer, this is probably a very slow implementation, possibly very broken, may cause compiler demons to possess your computer, DO NOT USE!)

I have left out some details for brevity, and it probably won't work in alot of situations, but it demonstrates the power of functional programming, quicksort in 4 lines (sort of, its not like Haskell's "quicksort in 2 lines" is any better mind you, its slow as balls because of all the memory allocation it has to do).

Anyway, yay for functional programming and thread derailment.

James
February 13, 2012
On 02/13/2012 03:19 PM, James Miller wrote:
> On 11 February 2012 10:45, Jonathan M Davis<jmdavisProg@gmx.com>  wrote:
>> On Friday, February 10, 2012 13:32:56 Marco Leise wrote:
>>> I know that feeling. I had no exposure to functional programming and
>>> options like chain never come to my head. Although "map" is a concept that
>>> I made friends with early.
>>
>> It would benefit your programming in general to learn a functional programming
>> language and become reasonably proficient in it, even if you don't intend to
>> program in it normally. It'll increase the number of tools in your programming
>> toolbox and improve your programming in other programming languages. It's
>> something that not enough programmers get sufficient exposure to IMHO.
>>
>> - Jonathan M Davis
>
> I found that learning Haskell made me significantly better at what I
> do. New paradigms are good for reminding you to think outside the box,
> I also learnt Prolog for a university course (AI) and that was an
> interesting challenge. Logical programming, where you define the
> boundaries of the program and then it works out the possible answers
> for you, amazingly useful for BNF grammars and similar constructs.
>
> If fact it's got to the point where I feel hamstrung if I can't do at
> least function passing (fortunately C, C++ and D can do this), and I
> prefer to work with languages that support closures and anonymous
> functions, since you can do wonders with simple constructs like map,
> fold (reduce) and filter. In fact a naive implementation of quicksort
> can be done succinctly in any language that supports filter.
>
>      T[] sort(T)(T[] array) {
>          pivot = array[array.length/2];
>          return sort(filter!("a<  "~pivot)(array)~pivot~sort(filter!("a
>> "~pivot)(array));
>      }
>
> (Disclaimer, this is probably a very slow implementation, possibly
> very broken, may cause compiler demons to possess your computer, DO
> NOT USE!)
>
> I have left out some details for brevity, and it probably won't work
> in alot of situations, but it demonstrates the power of functional
> programming, quicksort in 4 lines (sort of, its not like Haskell's
> "quicksort in 2 lines" is any better mind you, its slow as balls
> because of all the memory allocation it has to do).
>
> Anyway, yay for functional programming and thread derailment.
>
> James

If it is slow and uses an awful lot of auxiliary memory it is not quicksort as much as it may conceptually resemble quicksort. Try to implement in-place quicksort in Haskell. It will look like C code. Also see: http://stackoverflow.com/questions/5268156/how-do-you-do-an-in-place-quicksort-in-haskell

February 13, 2012
On 14 February 2012 06:25, Timon Gehr <timon.gehr@gmx.ch> wrote:
> On 02/13/2012 03:19 PM, James Miller wrote:
>>
>> On 11 February 2012 10:45, Jonathan M Davis<jmdavisProg@gmx.com>  wrote:
>>>
>>> On Friday, February 10, 2012 13:32:56 Marco Leise wrote:
>>>
>>>> I know that feeling. I had no exposure to functional programming and
>>>> options like chain never come to my head. Although "map" is a concept
>>>> that
>>>> I made friends with early.
>>>
>>>
>>> It would benefit your programming in general to learn a functional
>>> programming
>>> language and become reasonably proficient in it, even if you don't intend
>>> to
>>> program in it normally. It'll increase the number of tools in your
>>> programming
>>> toolbox and improve your programming in other programming languages. It's
>>> something that not enough programmers get sufficient exposure to IMHO.
>>>
>>> - Jonathan M Davis
>>
>>
>> I found that learning Haskell made me significantly better at what I do. New paradigms are good for reminding you to think outside the box, I also learnt Prolog for a university course (AI) and that was an interesting challenge. Logical programming, where you define the boundaries of the program and then it works out the possible answers for you, amazingly useful for BNF grammars and similar constructs.
>>
>> If fact it's got to the point where I feel hamstrung if I can't do at least function passing (fortunately C, C++ and D can do this), and I prefer to work with languages that support closures and anonymous functions, since you can do wonders with simple constructs like map, fold (reduce) and filter. In fact a naive implementation of quicksort can be done succinctly in any language that supports filter.
>>
>>     T[] sort(T)(T[] array) {
>>         pivot = array[array.length/2];
>>         return sort(filter!("a<  "~pivot)(array)~pivot~sort(filter!("a
>>>
>>> "~pivot)(array));
>>
>>     }
>>
>> (Disclaimer, this is probably a very slow implementation, possibly very broken, may cause compiler demons to possess your computer, DO NOT USE!)
>>
>> I have left out some details for brevity, and it probably won't work in alot of situations, but it demonstrates the power of functional programming, quicksort in 4 lines (sort of, its not like Haskell's "quicksort in 2 lines" is any better mind you, its slow as balls because of all the memory allocation it has to do).
>>
>> Anyway, yay for functional programming and thread derailment.
>>
>> James
>
>
> If it is slow and uses an awful lot of auxiliary memory it is not quicksort
> as much as it may conceptually resemble quicksort. Try to implement in-place
> quicksort in Haskell. It will look like C code. Also see:
> http://stackoverflow.com/questions/5268156/how-do-you-do-an-in-place-quicksort-in-haskell
>

It is still conceptually quicksort, the divide-and-conquer method based on partitioning the list. I wasn't writing it to show a valid implementation (I didn't even test it, it probably doesn't compile), I even warned of compiler demons! Its a demonstration of the succinctness of functional techniques for certain problems, not a show that functional languages "are teh awesum and all other langauges suck". Haskell is almost a pure functional language, therefore, under normal circumstances, every change to the array will allocate a new array, this is because of the whole immutability thing that it has going on. Of course I would never use such an implementation in real life, and Haskellers tend to avoid algorithms that do these kinds of things, using sorts like mergesort instead.

Saying "it is not quicksort as much as it may conceptually resemble quicksort" is kinda odd, its like saying "it is not a car, as much as it may conceptually resemble a car" because it doesn't run on petrol or gas, but instead runs on environment destroying orphan tears.

James Miller
February 13, 2012
On 02/13/2012 03:34 PM, James Miller wrote:

> Saying "it is not quicksort as much as it may conceptually resemble
> quicksort" is kinda odd, its like saying "it is not a car, as much as
> it may conceptually resemble a car" because it doesn't run on petrol
> or gas, but instead runs on environment destroying orphan tears.

For what its worth, Andrei uses that argument in his "On Iteration" article with "For starters, [one implementation of Haskell's] qsort is not really quicksort. Quicksort, as defined by Hoare in his seminal paper [8], is an in-place algorithm."

  http://www.informit.com/articles/printerfriendly.aspx?p=1407357

Ali

February 14, 2012
On 14 February 2012 12:45, Ali Çehreli <acehreli@yahoo.com> wrote:
> On 02/13/2012 03:34 PM, James Miller wrote:
>
>> Saying "it is not quicksort as much as it may conceptually resemble quicksort" is kinda odd, its like saying "it is not a car, as much as it may conceptually resemble a car" because it doesn't run on petrol or gas, but instead runs on environment destroying orphan tears.
>
> For what its worth, Andrei uses that argument in his "On Iteration" article with "For starters, [one implementation of Haskell's] qsort is not really quicksort. Quicksort, as defined by Hoare in his seminal paper [8], is an in-place algorithm."
>
>  http://www.informit.com/articles/printerfriendly.aspx?p=1407357
>
> Ali
>

Fair enough, I didn't realise that Quicksort was defined as in place, in that case, I retract my opposition to "not really a quicksort" however my "missing the point" still stands. I still prefer arrays over S-lists anyway, how else do I efficiently implement a heap?
February 14, 2012
On Tuesday, February 14, 2012 13:02:43 James Miller wrote:
> On 14 February 2012 12:45, Ali Çehreli <acehreli@yahoo.com> wrote:
> > On 02/13/2012 03:34 PM, James Miller wrote:
> >> Saying "it is not quicksort as much as it may conceptually resemble quicksort" is kinda odd, its like saying "it is not a car, as much as it may conceptually resemble a car" because it doesn't run on petrol or gas, but instead runs on environment destroying orphan tears.
> > 
> > For what its worth, Andrei uses that argument in his "On Iteration" article with "For starters, [one implementation of Haskell's] qsort is not really quicksort. Quicksort, as defined by Hoare in his seminal paper [8], is an in-place algorithm."
> > 
> > http://www.informit.com/articles/printerfriendly.aspx?p=1407357
> > 
> > Ali
> 
> Fair enough, I didn't realise that Quicksort was defined as in place, in that case, I retract my opposition to "not really a quicksort" however my "missing the point" still stands. I still prefer arrays over S-lists anyway, how else do I efficiently implement a heap?

Orphan tears. It's the only way to go.

- Jonathan M Davis
February 14, 2012
On 02/14/2012 12:34 AM, James Miller wrote:
> On 14 February 2012 06:25, Timon Gehr<timon.gehr@gmx.ch>  wrote:
>> On 02/13/2012 03:19 PM, James Miller wrote:
>>>
>>> On 11 February 2012 10:45, Jonathan M Davis<jmdavisProg@gmx.com>    wrote:
>>>>
>>>> On Friday, February 10, 2012 13:32:56 Marco Leise wrote:
>>>>
>>>>> I know that feeling. I had no exposure to functional programming and
>>>>> options like chain never come to my head. Although "map" is a concept
>>>>> that
>>>>> I made friends with early.
>>>>
>>>>
>>>> It would benefit your programming in general to learn a functional
>>>> programming
>>>> language and become reasonably proficient in it, even if you don't intend
>>>> to
>>>> program in it normally. It'll increase the number of tools in your
>>>> programming
>>>> toolbox and improve your programming in other programming languages. It's
>>>> something that not enough programmers get sufficient exposure to IMHO.
>>>>
>>>> - Jonathan M Davis
>>>
>>>
>>> I found that learning Haskell made me significantly better at what I
>>> do. New paradigms are good for reminding you to think outside the box,
>>> I also learnt Prolog for a university course (AI) and that was an
>>> interesting challenge. Logical programming, where you define the
>>> boundaries of the program and then it works out the possible answers
>>> for you, amazingly useful for BNF grammars and similar constructs.
>>>
>>> If fact it's got to the point where I feel hamstrung if I can't do at
>>> least function passing (fortunately C, C++ and D can do this), and I
>>> prefer to work with languages that support closures and anonymous
>>> functions, since you can do wonders with simple constructs like map,
>>> fold (reduce) and filter. In fact a naive implementation of quicksort
>>> can be done succinctly in any language that supports filter.
>>>
>>>      T[] sort(T)(T[] array) {
>>>          pivot = array[array.length/2];
>>>          return sort(filter!("a<    "~pivot)(array)~pivot~sort(filter!("a
>>>>
>>>> "~pivot)(array));
>>>
>>>      }
>>>
>>> (Disclaimer, this is probably a very slow implementation, possibly
>>> very broken, may cause compiler demons to possess your computer, DO
>>> NOT USE!)
>>>
>>> I have left out some details for brevity, and it probably won't work
>>> in alot of situations, but it demonstrates the power of functional
>>> programming, quicksort in 4 lines (sort of, its not like Haskell's
>>> "quicksort in 2 lines" is any better mind you, its slow as balls
>>> because of all the memory allocation it has to do).
>>>
>>> Anyway, yay for functional programming and thread derailment.
>>>
>>> James
>>
>>
>> If it is slow and uses an awful lot of auxiliary memory it is not quicksort
>> as much as it may conceptually resemble quicksort. Try to implement in-place
>> quicksort in Haskell. It will look like C code. Also see:
>> http://stackoverflow.com/questions/5268156/how-do-you-do-an-in-place-quicksort-in-haskell
>>
>
> It is still conceptually quicksort, the divide-and-conquer method
> based on partitioning the list.

Hoare's original quicksort algorithm is more detailed than what is sketched here. The main point is the in-place partition operation with the two pointers approaching each other.

> I wasn't writing it to show a valid
> implementation (I didn't even test it, it probably doesn't compile), I
> even warned of compiler demons! Its a demonstration of the
> succinctness of functional techniques for certain problems, not a show
> that functional languages "are teh awesum and all other langauges
> suck".

The approach given does not solve the problem (it does not implement Quicksort). Quicksort in Haskell looks like Quicksort in D, because the algorithm depends on destructive updates. Functional techniques can be succinct for certain problems, but implementing Quicksort is not one of them.

> Haskell is almost a pure functional language, therefore, under
> normal circumstances, every change to the array will allocate a new
> array,

Haskell can do destructive array updates that look like pure operations just fine. http://hackage.haskell.org/packages/archive/array/0.2.0.0/doc/html/Data-Array-MArray.html

> this is because of the whole immutability thing that it has going on.

This is confusing the abstraction with its implementation. It is impossible to recreate Haskell's execution semantics in D using only immutable types.

> Of course I would never use such an implementation in real
> life, and Haskellers tend to avoid algorithms that do these kinds of
> things, using sorts like mergesort instead.
>

Mostly lazy mergesort if I'm not mistaken. And they don't usually use it to sort arrays, they sort lists. Haskell arrays ought to be sorted with introsort if the comparison operation is cheap.

> Saying "it is not quicksort as much as it may conceptually resemble
> quicksort" is kinda odd, its like saying "it is not a car, as much as
> it may conceptually resemble a car" because it doesn't run on petrol
> or gas, but instead runs on environment destroying orphan tears.
>

It is more like saying "a handcart is not a car, as much as it may conceptually resemble a car" (the engine is missing!).

February 15, 2012
MattCodr wrote:

> I have a doubt about the best way to insert and move (not replace) some data on an array.

I have the vision, that a mapping from a dense range of integers to some value type and wast (i.e. Theta( n)) changes of this mapping are a severe hint for a maldesign.

-manfred
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