March 09, 2006
Hello,

With the new IFTI support I have been looking at ways of upgrading the standard library with new and more generic functions. What follows is my suggestions for functions to be added to std.array. I have implemented all of them and the current (0.149) limited IFTI-support is enough to support them. That being said, I wish to hold off making a source code submission until a) I get review comments on the suggested function prototypes and b) it is more clear how far D is taking IFTI support (meaning possibly neater implementation).

All functions are designed to be used both as free function and as implicit array methods. Except for the inplace versions, no functions modifies the array.

The prototype notation is my own. a|b means two alternative types. T is the generic element type. T[] is the array.

-----------

T fold(T[] arr, T init, T delegate|function combiner(T,T));

Generic array recursion function. combiner is called recursively:
	return combiner(init,fold(arr[1..$],arr[0],combiner));
(The actual implementation will of course call the combiner iteratively)


T max(T[] arr)

Returns the maximum element in arr as defined by the > operator.


T min(T[] arr)

Returns the minimum element in arr as defined by the < operator.


T sum(T[] arr)

Returns the sum of the element in arr as defined by the + operator.


ptrdiff_t find(T[] arr, T|delegate|function d);

Returns the index of the first occurence of d or the first true predicate d applied to the elements in order. Returns -1 when no element is found.


size_t indexOf(T[] arr, T|delegate|function d);

Like find, but throws on missing element.


T[][] split(T[] arr, T|T[]|delegate|function d);

Split the array arr using a predicate/element/subarray d.
(obsoletes std.string.split that only works for char[])


T[] join(T[][] arr, T|T[]|delegate|function separator);

Join the elements array arr using separator.
(obsoletes std.string.join that only works for char[])


T[] join(T[][] arr);

Join the array T[][] without separator.


U[] map(T[] arr, U delegate|function f(T));

Map the elements of arr over function f, returning an array of the results.


T[] filter(T[] arr, delegate|function p(T));

Filters arr over the predicate p, returning array of elements of arr where the predicate is true.


Possible inplace version of map:

T[] doMap(T[], T delegate|function f(T));

---------

I would also prefer those over the language built in .sort .reverse:

T[] sort(T[]);
T[] stableSort(T[]);
T[] sort(T[], delegate|function wrongOrder(T,T));
T[] reverse(T[]);


With the corresponding inplace versions:

T[] doSort(T[]);
T[] doStableSort(T[]);
T[] doSort(T[], delegate|function wrongOrder(T,T));
T[] doReverse(T[]);

---------

Is there in general even any interest in adding generic functions to the standard library?

Regards,

Oskar
March 09, 2006
"Oskar Linde" <oskar.lindeREM@OVEgmail.com> wrote in message news:dup4fr$2c0b$3@digitaldaemon.com...
> Hello,
>
> With the new IFTI support I have been looking at ways of upgrading the standard library with new and more generic functions. What follows is my suggestions for functions to be added to std.array. I have implemented all of them and the current (0.149) limited IFTI-support is enough to support them. That being said, I wish to hold off making a source code submission until a) I get review comments on the suggested function prototypes and b) it is more clear how far D is taking IFTI support (meaning possibly neater implementation).
>
> All functions are designed to be used both as free function and as implicit array methods. Except for the inplace versions, no functions modifies the array.
>
> The prototype notation is my own. a|b means two alternative types. T is the generic element type. T[] is the array.
>
> -----------
>
> T fold(T[] arr, T init, T delegate|function combiner(T,T));
>
> Generic array recursion function. combiner is called recursively:
> return combiner(init,fold(arr[1..$],arr[0],combiner));
> (The actual implementation will of course call the combiner iteratively)
>
>
> T max(T[] arr)
>
> Returns the maximum element in arr as defined by the > operator.
>
>
> T min(T[] arr)
>
> Returns the minimum element in arr as defined by the < operator.
>
>
> T sum(T[] arr)
>
> Returns the sum of the element in arr as defined by the + operator.
>
>
> ptrdiff_t find(T[] arr, T|delegate|function d);
>
> Returns the index of the first occurence of d or the first true predicate d applied to the elements in order. Returns -1 when no element is found.
>
>
> size_t indexOf(T[] arr, T|delegate|function d);
>
> Like find, but throws on missing element.
>
>
> T[][] split(T[] arr, T|T[]|delegate|function d);
>
> Split the array arr using a predicate/element/subarray d. (obsoletes std.string.split that only works for char[])
>
>
> T[] join(T[][] arr, T|T[]|delegate|function separator);
>
> Join the elements array arr using separator.
> (obsoletes std.string.join that only works for char[])
>
>
> T[] join(T[][] arr);
>
> Join the array T[][] without separator.
>
>
> U[] map(T[] arr, U delegate|function f(T));
>
> Map the elements of arr over function f, returning an array of the results.
>
>
> T[] filter(T[] arr, delegate|function p(T));
>
> Filters arr over the predicate p, returning array of elements of arr where the predicate is true.
>
>
> Possible inplace version of map:
>
> T[] doMap(T[], T delegate|function f(T));
>
> ---------
>
> I would also prefer those over the language built in .sort .reverse:
>
> T[] sort(T[]);
> T[] stableSort(T[]);
> T[] sort(T[], delegate|function wrongOrder(T,T));
> T[] reverse(T[]);
>
>
> With the corresponding inplace versions:
>
> T[] doSort(T[]);
> T[] doStableSort(T[]);
> T[] doSort(T[], delegate|function wrongOrder(T,T));
> T[] doReverse(T[]);
>
> ---------
>
> Is there in general even any interest in adding generic functions to the standard library?
>
> Regards,
>
> Oskar
I like it.  It would be especially cool if we could get rid of the necessary () after each call when using property syntax, thus making truely plugable properties.


March 09, 2006
Oskar Linde wrote:
> Hello,
> 
> With the new IFTI support I have been looking at ways of upgrading the standard library with new and more generic functions. 

[snip]
> Is there in general even any interest in adding generic functions to the
> standard library?

Some of these functions are the last thing remaining in std.math2 (but they definitely don't below there, none of them are truly mathematical). We definitely want to remove std.math2 prior to 1.0, std.array sounds good to me.

I'll just comment on one function:

> T sum(T[] arr)
>
> Returns the sum of the element in arr as defined by the + operator.

This one has an interesting twist. I'm not sure that the sum should necessarily be of type T. I've been playing around with the concept of what I've called the Archetype of a type, which is the largest type with the same semantics as T (possibly with the same calculation speed). (ie,
Archetype!(byte)= Archetype!(short)
Archetype!(int) = long
Archetype!(float) = Archetype!(double) = real,
Archetype!(cfloat)= creal, etc). Obviously it's a trivial template.

I think that at least,  sum(double[] ) should internally use a real while accumulating the sum, so that it can satisfy this test (at least on x86 platforms):

unittest {
   const double a = [ double.max, double.max, -double.max];
   assert(sum(a) == double.max);
}

After all, this is one of the reasons why reals exist. I'm still not sure if sum(double []) should return a double or a real, although I'm inclined to think that *any* function that returns a single floating point value should return a real (on x87, the 80-bit result is just left on the FPU stack anyway). But, I'm less confident about how a sum of ints should behave.

However, all the other functions seem to be free of mathematical subtleties. sum() is the only one which involves arithmetic operators, and therefore it might not belong with the rest.
March 09, 2006
Ameer Armaly wrote:
> "Oskar Linde" <oskar.lindeREM@OVEgmail.com> wrote in message news:dup4fr$2c0b$3@digitaldaemon.com...
>> Hello,
>>
>> With the new IFTI support I have been looking at ways of upgrading the standard library with new and more generic functions. What follows is my suggestions for functions to be added to std.array. I have implemented all of them and the current (0.149) limited IFTI-support is enough to support them. That being said, I wish to hold off making a source code submission until a) I get review comments on the suggested function prototypes and b) it is more clear how far D is taking IFTI support (meaning possibly neater implementation).
>>
>> All functions are designed to be used both as free function and as implicit array methods. Except for the inplace versions, no functions modifies the array.
>>
>> The prototype notation is my own. a|b means two alternative types. T is the generic element type. T[] is the array.
>>
>> -----------
>>
>> T fold(T[] arr, T init, T delegate|function combiner(T,T));
>>
>> Generic array recursion function. combiner is called recursively:
>> return combiner(init,fold(arr[1..$],arr[0],combiner));
>> (The actual implementation will of course call the combiner iteratively)
>>
>>
>> T max(T[] arr)
>>
>> Returns the maximum element in arr as defined by the > operator.
>>
>>
>> T min(T[] arr)
>>
>> Returns the minimum element in arr as defined by the < operator.
>>
>>
>> T sum(T[] arr)
>>
>> Returns the sum of the element in arr as defined by the + operator.
>>
>>
>> ptrdiff_t find(T[] arr, T|delegate|function d);
>>
>> Returns the index of the first occurence of d or the first true predicate d applied to the elements in order. Returns -1 when no element is found.
>>
>>
>> size_t indexOf(T[] arr, T|delegate|function d);
>>
>> Like find, but throws on missing element.
>>
>>
>> T[][] split(T[] arr, T|T[]|delegate|function d);
>>
>> Split the array arr using a predicate/element/subarray d.
>> (obsoletes std.string.split that only works for char[])
>>
>>
>> T[] join(T[][] arr, T|T[]|delegate|function separator);
>>
>> Join the elements array arr using separator.
>> (obsoletes std.string.join that only works for char[])
>>
>>
>> T[] join(T[][] arr);
>>
>> Join the array T[][] without separator.
>>
>>
>> U[] map(T[] arr, U delegate|function f(T));
>>
>> Map the elements of arr over function f, returning an array of the results.
>>
>>
>> T[] filter(T[] arr, delegate|function p(T));
>>
>> Filters arr over the predicate p, returning array of elements of arr where the predicate is true.
>>
>>
>> Possible inplace version of map:
>>
>> T[] doMap(T[], T delegate|function f(T));
>>
>> ---------
>>
>> I would also prefer those over the language built in .sort .reverse:
>>
>> T[] sort(T[]);
>> T[] stableSort(T[]);
>> T[] sort(T[], delegate|function wrongOrder(T,T));
>> T[] reverse(T[]);
>>
>>
>> With the corresponding inplace versions:
>>
>> T[] doSort(T[]);
>> T[] doStableSort(T[]);
>> T[] doSort(T[], delegate|function wrongOrder(T,T));
>> T[] doReverse(T[]);
>>
>> ---------
>>
>> Is there in general even any interest in adding generic functions to the standard library?
>>
>> Regards,
>>
>> Oskar

Upon rereading, I realized that the inplace versions should be void functions - not returning an array.

> I like it.  It would be especially cool if we could get rid of the necessary () after each call when using property syntax, thus making truely plugable properties. 

Yes, I agree. I would like to know if all pairs of empty parentheses after functions are supposed to be redundant or if calls without parentheses should be reserved to property like methods. Considering the current .sort and .reverse semantics, I guess the former is the case and DMD not allowing calls without parentheses for implicit array methods is an unintentional omission.

/Oskar
March 09, 2006
Don Clugston wrote:
> Oskar Linde wrote:
> I'll just comment on one function:
> 
>  > T sum(T[] arr)
>  >
>  > Returns the sum of the element in arr as defined by the + operator.
> 
> This one has an interesting twist. I'm not sure that the sum should necessarily be of type T. I've been playing around with the concept of what I've called the Archetype of a type, which is the largest type with the same semantics as T (possibly with the same calculation speed). (ie,
> Archetype!(byte)= Archetype!(short)
> Archetype!(int) = long
> Archetype!(float) = Archetype!(double) = real,
> Archetype!(cfloat)= creal, etc). Obviously it's a trivial template.

Interesting...

> I think that at least,  sum(double[] ) should internally use a real while accumulating the sum, so that it can satisfy this test (at least on x86 platforms):
> 
> unittest {
>    const double a = [ double.max, double.max, -double.max];
>    assert(sum(a) == double.max);
> }
> 
> After all, this is one of the reasons why reals exist. I'm still not sure if sum(double []) should return a double or a real, although I'm inclined to think that *any* function that returns a single floating point value should return a real (on x87, the 80-bit result is just left on the FPU stack anyway). But, I'm less confident about how a sum of ints should behave.

Int overflows is well defined, making the sum of ints behave correctly in the case above. Int is also the promotion type for integral operations and would be the natural return type for sum(int[]). A sum of shorts should probably return an int though, following integer promotion rules. Should Archetype for integers follow the integer promotion rules or all be long?

> However, all the other functions seem to be free of mathematical subtleties. sum() is the only one which involves arithmetic operators, and therefore it might not belong with the rest.

You make a strong argument and I agree. sum() is used as join() in other languages that lack the distinction between addition and concatenation. D doesn't need a non-arithmetic sum function. With the proposed fold function, you could also easily implement sum as:

sum = fold(arr,0,int function(int a, int b) { return a+b; });

prod = fold(arr,1,int function(int a, int b) { return a*b; });

Or generic, using Archetype:

fold(arr,0,Archetype!(T) function(Archetype!(T) a, T b) {return a+b;});

/Oskar
March 09, 2006
Oskar Linde wrote:
> sum = fold(arr,0,int function(int a, int b) { return a+b; });
> prod = fold(arr,1,int function(int a, int b) { return a*b; });
> fold(arr,0,Archetype!(T) function(Archetype!(T) a, T b) {return a+b;});
Oops, those should of course read:

sum = fold(arr,0, function int(int a, int b) { return a+b; });
prod = fold(arr,1, function int(int a, int b) { return a*b; });
fold(arr,0, function Archetype!(T)(Archetype!(T) a, T b) {return a+b;});

/Oskar
March 09, 2006
Oskar Linde wrote:

...

Totally agree that something like this (and more) should be in the standard library.

> 
> Upon rereading, I realized that the inplace versions should be void functions - not returning an array.

Not sure about this one. Returning an array allows chaining:

array.doMap(someDelegate).doSort();

...

> 
>> I like it.  It would be especially cool if we could get rid of the necessary () after each call when using property syntax, thus making truely plugable properties. 
> 
> 
> Yes, I agree. I would like to know if all pairs of empty parentheses after functions are supposed to be redundant or if calls without parentheses should be reserved to property like methods. Considering the current .sort and .reverse semantics, I guess the former is the case and DMD not allowing calls without parentheses for implicit array methods is an unintentional omission.
> 
> /Oskar
March 09, 2006
Ivan Senji wrote:
> Oskar Linde wrote:
> 
> ...
> 
> Totally agree that something like this (and more) should be in the standard library.

Please elaborate on (and more).

>> Upon rereading, I realized that the inplace versions should be void functions - not returning an array.
> 
> Not sure about this one. Returning an array allows chaining:
> 
> array.doMap(someDelegate).doSort();

Yes, but void removes the chance of using inplace versions by mistake and makes it extra obvious that they are not ordinary functions. I think this is more important than the ability of chaining.

/Oskar
March 09, 2006
"Oskar Linde" <oskar.lindeREM@OVEgmail.com> wrote in message news:dup4fr$2c0b$3@digitaldaemon.com...
> With the corresponding inplace versions:
>
> T[] doSort(T[]);
> T[] doStableSort(T[]);
> T[] doSort(T[], delegate|function wrongOrder(T,T));
> T[] doReverse(T[]);
>

My only reservation would be the decision to prefix these functions with "do". It's tautological and doesn't express anything about them being in-place versions. I suggest just calling them sortInPlace/inPlaceSort (or even sortInSitu or inSituSort).


March 09, 2006
Oskar Linde wrote:
> Ivan Senji wrote:
> 
>> Oskar Linde wrote:
>>
>> ...
>>
>> Totally agree that something like this (and more) should be in the standard library.
> 
> 
> Please elaborate on (and more).
> 

:P I knew you were going to say that. I was just trying to say that the new features open up a lot of possibilites. (not trying to say you didn't to a great job, more that there is more that could be done in a standard library)

No ideas at the moment, but when I think of something I'll let you know.


>>> Upon rereading, I realized that the inplace versions should be void functions - not returning an array.
>>
>>
>> Not sure about this one. Returning an array allows chaining:
>>
>> array.doMap(someDelegate).doSort();
> 
> 
> Yes, but void removes the chance of using inplace versions by mistake and makes it extra obvious that they are not ordinary functions. I think this is more important than the ability of chaining.
> 

What you say does make sense. But I don't think it would be souch a big problem. It is always safe to use ordinary array functions, and it would be nice to be able to just replace them with inplace ones for performance reasons if the original array is not needed any more.

So if I have:
array.map(someDelegate).sort();

and I figure out that it could be optimized because I don'n need the original array I could just change the functions used.

But if the general consensus would be for inplace functions to return void I would have to agree :)
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