as double adverb,
lr =: 3 : '5!:5 < ''y'''
break =: 1 : '(`(lr@] 13!:8 1:))(@.u)'
+: (0 = ]) break("0) 2 3 0 1
|0
| +:(0=])break("0)2 3 0 1
+:(0 e.])break 2 3 0 1
|2 3 0 1
| +:(0 e.])break 2 3 0 1
no error,
+:(0=])break("0)2 3 10 1
4 6 20 2
But the missing feature is I think is tacit return. I understand there is
already a lot of special code, but as a problem example
find the largest cummulative sum +/\ under 1e6. What if your list has a
billion items?
syntax would be something like: Returnif is conjunction.
+Returnif (1e6 < ])/\
The internals would be that the argument to other adverb (/ in this case) would
be a special gerund of u ar (,<) 'R.' , v ar . And it is up to each adverb to
implement how it handles R.
But a more general solution would be a 13!: code similar to 13!:8 but does not
halt. Consider:
1!:2&2@:+: (0 = ]) break("0) 2 3 0 1
4
6
|0
| 1!:2&2@:+:(0=])break("0)2 3 0 1
if returnif was defined similar to break but used the codes below:
+:(1=])return("0)2 3 1 11
the 13!:81 code would return 4 6 normally, (does not execute last call before
return)
x 13!:82 would return 4 6 2 . double of 1 included in list.
13!:83 would return (0$0.5) ,&< resultsofar (4 6)
x 13!:84 would return (0$0.5) ,&< resultplus1more(x) (4 6 2)
the 0$0.5 code is optional, but basically allows functional error handling,
where you don't want any halting but you can guard results from further
processing. Codes similar to C and socket library also work so 0 ,&< y for no
error. And some number designated as early return (I recommend positive
numbers for "halting" errors, and negative numbers for contextual info about
result. reserving _1 for early return would seem fine)
The 13!:8x codes can be simplified from 4 to 2. the y argument to them is the
return value (can be any type), and null ('') signals to return nothing. It
would be up to the user if they want to do 1 more execution to return extra
result or not. J is pretty good at assembling nulls with other data.
Here is something weird I noticed btw,
1!:2&2@:+/ i.5
7
9
10
10
10
Id expect to see the same numbers as
+/\ i.5
0 1 3 6 10
----- Original Message -----
From: Henry Rich <henryhr...@gmail.com>
To: sou...@jsoftware.com
Sent: Wednesday, August 3, 2016 6:29 PM
Subject: Re: [Jsource] F. WAS: Proposal for new looping primitive x N.
This is a very good idea. Perhaps gerund v could be (selection
function)`(termination function)
or
perhaps we could define a 'termination' error code that would be
signaled with 13!:8
or maybe someone has a better way.
Henry Rich
On 8/3/2016 3:42 PM, Joe Bogner wrote:
> I like the sound of it. Really happy to hear about a new language feature.
>
> Just a thought - is there any reason to have a way to specify an
> early-termination condition, so the entire set of data doesn't need to be
> evaluated? I don't have a specific use case in mind, so it's not worth it
> if others don't either
>
>
>
> On Wed, Aug 3, 2016 at 9:11 AM, Henry Rich <henryhr...@gmail.com> wrote:
>
>> Thanks for the ideas, guys. New proposal below.
>>
>> Let's keep the definition in explicit form, so that we can have more
>> readers involved.
>>
>> u/\ has no place here: it requires u to be associative.
>>
>> Definition:
>>
>> [x] u F. v y
>>
>> where
>>
>> u is a verb to be applied repeatedly
>> v is a verb to apply to the result of each execution of u, to
>> produce the part saved in the final result, or [: to get the full result
>> of only the final execution of u
>> x is the (optional) initial value (if omitted, u is applied first
>> between the last 2 items of y)
>> y is the argument array
>> F. applies between items of y starting at the end, F: starts at the
>> front. In either case the x argument to u is the next item of y, and the y
>> argument to u is the initial value/state from previous execution.
>>
>> Formal definition:
>> Fdot =: 2 : 0
>> cap =. [:
>> if. 'v' -:&(5!:1)&< 'cap' do.
>> u&:>/ (<"_1 y)
>> else.
>> v@> u&.>/\. (<"_1 y)
>> end.
>> :
>> cap =. [:
>> if. 'v' -:&(5!:1)&< 'cap' do.
>> u&:>/ (<"_1 y) , <x
>> else.
>> v@> u&.>/\. (<"_1 y) , <x
>> end.
>> )
>>
>> Fcolon =: 2 : 0
>> cap =. [:
>> if. 'v' -:&(5!:1)&< 'cap' do.
>> u&:>/@|. (<"_1 y)
>> else.
>> v@> u&.>/\.&.|. (<"_1 y)
>> end.
>> :
>> cap =. [:
>> if. 'v' -:&(5!:1)&< 'cap' do.
>> u&:>/ (|. <"_1 y) , <x
>> else.
>> v@> u&.>/\.&.|. (<"_1 y) ,~ <x
>> end.
>> )
>>
>>
>>
>> Example:
>>
>> f =. ((i. , ]) >./)@:(({:@])`({.@])`[})
>>
>> this takes x=list and y=index,value. It stores value into x at location
>> index, and returns the index and value of the largest atom in the resulting
>> list. (Yeah, it's a punk function.)
>>
>> 0 0 f Fdot (1&{) a =: 20 20 ?@$ 10099 99 99 99 99 99 99 99 99 99 99 99
>> 99 99 99 99 99 99 99 96 0
>>
>>
>> The result is the list of the indexes that were encountered.
>>
>> 0 0 f Fdot [: a =: 20 20 ?@$ 100
>>
>> 2 99
>>
>>
>> The result is the result of the last execution only.
>>
>>
>> Henry Rich
>>
>>
>> On 8/3/2016 4:11 AM, 'Pascal Jasmin' via Source wrote:
>>
>>> posting code before words,
>>>
>>> reduce2 =: (((&.>)/)(>@:))(@:(<"_1@:[ , <@:]))
>>> reduce3 =: ((((&.>)/)\.)(>@:))(@:(<"_1@:[ , <@:]))
>>>
>>> Rdot =: 2 : '>@:(u&.>(n aar 5!:0))@:(<"_1@:[ , <@:])'
>>> Rdot1 =: 2 : '>@:(u&.>(n aar 5!:0))@:(<"_1@:[ ,~ <@:])'
>>>
>>> + reduce2
>>>
>>>> @:(+&.>/)@:(<"_1@:[ , <@:])
>>>>
>>> + Rdot '/'
>>>
>>>> @:(+&.>/)@:(<"_1@:[ , <@:])
>>>>
>>> + reduce2
>>>
>>>> @:(+&.>/)@:(<"_1@:[ , <@:])
>>>>
>>> + reduce3
>>>
>>>> @:(+&.>/\.)@:(<"_1@:[ , <@:])
>>>>
>>> + Rdot '/\.'
>>>
>>>> @:(+&.>/\.)@:(<"_1@:[ , <@:])
>>>>
>>> They are grouped by equivalent use. Rdot1 reverses the order, but the
>>> only point of that seems to use (Rdot1 '/\') instead of Rdot '/\.' Rdot1
>>> '/\' could easily have a reduce4 adverb "predefinition".
>>>
>>>
>>> The first thing you seem to be missing is using just / instead of /\.
>>> Its a much more common use. The next point is that Ndot1 probably should
>>> use /\ instead of /\.
>>>
>>>
>>>
>>> 1 2 + Rdot'/'~ 1 2 3 4
>>> 11 12
>>> 1 2 + Rdot'/\.'~ 1 2 3 4
>>> 11 12
>>> 10 11
>>> 8 9
>>> 5 6
>>> 1 2
>>> 1 2 + Rdot1'/\'~ 1 2 3 4
>>> 1 2
>>> 2 3
>>> 4 5
>>> 7 8
>>> 11 12
>>>
>>> Rdot1 isn't absolutely necessary because (u Rdot'/\.'~ |.) will produce
>>> all of the same items in reverse order.
>>>
>>>
>>>
>>> I don't think any other use case makes sense. And I don't see a monadic
>>> application making sense either. A monad would just use / or /\. or /\
>>> instead. The other model is:
>>>
>>>
>>> reducE =: 1 : (':'; 'o=. x for_i. y do. o =. o u i end.')
>>>
>>> which is the same as u~ reduce2~
>>>
>>>
>>> The next point to notice is that the pattern (adverb) (>@:)(@:(<"_1@:[ ,
>>> <@:])) imposes a guarantee on its u argument to produce a consistent
>>> shape. In terms of looking for special code, there's just 2 necessary
>>> patterns on the left: (&.>/) or (&.>/\.)
>>>
>>> bit 1: if / and /\. are the only practical uses of this, then the result
>>> can always be unboxed at the end. because u&.>/ started with 2 boxes on.
>>> If u wants to add "extra" box layers, then u can do so, and it is up to u
>>> to figure out a consistent interpretation. Usually pretty straightforward,
>>> but I'd need to see a use case for bit1 "auto-boxing" that is diffucult to
>>> do in u.
>>>
>>> imo bit0 is not needed, but bit 2 is / or /\. . A 3rd conceivable use
>>> that may be too esoteric is instead of (<"_1@:[ , <@]) :
>>> <@(<\@:[ ,. <@]) or
>>> <@(<\.@:[ ,. <@])
>>>
>>>
>>> this builds boxes of lists of boxes, and is different from the "core
>>> pattern" I described above. What seems to actually be the core pattern is
>>> the 2:
>>>
>>> ((&.>)/)(>@:)(list of boxings adverb)
>>>
>>> ((&.>)/\.)(>@:)(list of boxings adverb)
>>>
>>> where the "list of boxings adverb" could be limited to:
>>>
>>> @:(u(<"_1@:) , v(<@:)) and maybe
>>> @:(u(<"_1@:) ,~ v(<@:))
>>>
>>> u and v can maybe even be limited to [ ]
>>>
>>> there's a similar pattern in ,&< ... We know that both sides (and that
>>> count = 2) were homogeneous prior to their boxings. In the case of
>>>
>>>
>>> (>@:)(list of boxings adverb)
>>>
>>> we know that u (to left of this adverb) must create a homogeneous result
>>> (or error). In addition to fold/scan operations, u can also be something
>>> like x&{ leaf.
>>>
>>> in the context of fold/scan,
>>>
>>> fold(initialstate, array, function) the u and v in the above pattern are
>>> initialstate and array. As you know, the optimization potential is that
>>> they never have to be boxed. The point of the rambling, is that there is a
>>> more general pattern in (>@:)(@:(boxing of 2 variables verb))
>>>
>>> I'd recommend against putting an extra function parameter for twiddling
>>> (reversing) x or y. I think its better for user to pretweak them, or they
>>> can write/use a modifier that adds the functionality.
>>>
>>>
>>> about v,
>>>
>>> your implementation I think means that it can only be a noun, and so I
>>> think the result would always have a compatible shape, and so no need to
>>> box it. An alternative to a v parameter to function is special code for
>>>
>>> (v {"_1 (bound N.)), and then consider {. {: # without the "_1
>>> restriction.
>>> (v {"1 _1 L:0 _ (bound N.)) might also solve the box/no box bit.
>>>
>>>
>>> A problem with having a v embedded parameter in the modifier is that it
>>> may be a function of the data. 90%+ of the time, you will want all of it.
>>> A selection formula might be (<@i.@#"_1 {"1 _1 leaf ]) even though the
>>> same (selection vector) value would most likely be generated for all
>>> items. Basically having a v parameter embedded in the modifier would mean
>>> instead of
>>>
>>> v&{&.> u&.>/\. (<"_1 y) , <x
>>>
>>> have
>>>
>>> v&.> u&.>/\. (<"_1 y) , <x
>>>
>>> This would let ] be a simple v parameter to get the full results. In
>>> terms of optimization, you may not need to care whether # or {. is used.
>>> The shape is not guaranteed linear either, so v may be much more complex
>>> than a noun argument to { .
>>>
>>> The v parameter is obviously not needed for / version. Seperate
>>> functions are good if you accept that both are useful. But you can also
>>> look at it as 3 function patterns
>>>
>>> u (((&.>)/)(>@:))(@:(boxing of 2 variables)) (reduce2)
>>> u reduce3(v&>@:) NB. /\. version
>>>
>>> u reduce3(v&.>@:)
>>>
>>> But for the latter 2, it may be better and simpler to do it through
>>> special code detection? If you call either
>>>
>>> (u reduce3)(v&.>@:)
>>> or
>>>
>>> v&.>@:(u reduce3)
>>>
>>> then v can get "optimized within the main loop"
>>>
>>>
>>> ----- Original Message -----
>>> From: Henry Rich <henryhr...@gmail.com>
>>> To: Source forum <sou...@jsoftware.com>
>>> Sent: Tuesday, August 2, 2016 8:43 PM
>>> Subject: [Jsource] Proposal for new looping primitive x N.
>>>
>>> As Marshall once noted, the biggest deficiency in J is looping over an
>>> array when you need a result from each iteration, and the calculation
>>> requires an initial value and some internal state. Your code looks like
>>>
>>> result {"_1 f/\. array , initialstate
>>>
>>> where each execution of f produces a result value plus the internal
>>> state to feed into the next iteration. The problems are:
>>> * the result is the entire array of internal state, which is more, maybe
>>> MUCH more than you need, since the final result needs only a portion of
>>> the state
>>> * The state is probably not commensurate with a item of the array, so
>>> you end up boxing the initial state and the array items, which is very
>>> wasteful.
>>>
>>> I propose a new primitive, call it N. (for insert). N. is an adverb
>>> that produces a conjunction. In (x N.), x specifies options for the
>>> processing, much as the right operand of u;.n does.
>>>
>>> Definition:
>>>
>>> [x] u (n N.) v y
>>>
>>> where
>>>
>>> u is the function to be applied
>>> v is the selector to apply to the result of each execution of u, to
>>> produce the part saved in the final result
>>> x is the (optional) initial value (if omitted, f is applied first
>>> between the last 2 items of y)
>>> y is the argument array
>>> n selects from several variants:
>>> bit 0=0 operation goes back to front
>>> bit 0=1 operation goes front to back, as if using &.|.
>>> bit 1=0 selected result from each iteration becomes one item of result
>>> bit 1=1 selected result from each iteration is boxed before becoming
>>> an item of result
>>>
>>> Formal definition:
>>> Ndot0 =: 2 : 0
>>> v&{@> u&.>/\. (<"_1 y)
>>> :
>>> v&{@> u&.>/\. (<"_1 y) , <x
>>> )
>>> Ndot1 =: 2 : 0
>>> v&{@> u&.>/\.&.|. (<"_1 y)
>>> :
>>> v&{@> u&.>/\.&.|. (<"_1 y) ,~ <x
>>> )
>>> Ndot2 =: 2 : 0
>>> v&{&.> u&.>/\. (<"_1 y)
>>> :
>>> v&{&.> u&.>/\. (<"_1 y) , <x
>>> )
>>> Ndot3 =: 2 : 0
>>> v&{&.> u&.>/\.&.|. (<"_1 y)
>>> :
>>> v&{&.> u&.>/\.&.|. (<"_1 y) ,~ <x
>>> )
>>>
>>> Ndot =: 1 : 0
>>> assert. m e. i. 4
>>> select. m
>>> case. 0 do. Ndot0
>>> case. 1 do. Ndot1
>>> case. 2 do. Ndot2
>>> case. 3 do. Ndot3
>>> end.
>>> )
>>>
>>>
>>> I look forward to criticism of this proposal.
>>>
>>> Henry Rich
>>>
>>> ----------------------------------------------------------------------
>>> For information about J forums see http://www.jsoftware.com/forums.htm
>>> ----------------------------------------------------------------------
>>> For information about J forums see http://www.jsoftware.com/forums.htm
>>>
>> ----------------------------------------------------------------------
>> For information about J forums see http://www.jsoftware.com/forums.htm
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
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For information about J forums see http://www.jsoftware.com/forums.htm
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