Most J programmers don't try to do everything functionally.
I write tacit programs for things that have a crystal-clear spec and
will not require much maintenance. Everything else is explicit.
Henry Rich
On 6/7/2017 2:26 PM, Michael Rice wrote:
@Raul Miller
Thanks for the paste tip. I was unaware of that feature.
I'm "giving up on" the peg game. I didn't think that needed identifying as
it's been my only focus. I think of "academic exercises" as homework,
seeking answers to which is, rightly, taboo on computer language web-sites.
The peg game search function has five arrays it recursively manipulates to
a solution, three of which begin as empty, all having varying shapes, even
empty, as they pass through recursions. From what I've read in *Learning J*,
for their heterogeneous shapes they would have to be boxed to be passed as
a functional parameter, un-boxed inside a recursive pass to be altered, and
then boxed again to be passed on to the next recursion. I didn't say it was
impossible, just that it seemed kludgy, or, as you put it "forced."
I spent quite a bit of time with Haskell. As a functional language it's
hard to beat, but some problems on which I used it I felt like I was having
to go around the block just to get next door. Why bother?
Thanks for your input.
On Wed, Jun 7, 2017 at 1:11 PM, Raul Miller <[email protected]> wrote:
When pasting into gmail, please use "Paste and match style" to avoid
the extra blank lines that someone at google somehow managed to work
into the default Paste action.
That said:
my_empty =: }. 1
< my_empty
┌┐
││
└┘
What you are seeing here is not an empty list of boxes but a box
containing an empty. Or, ok, yes: "an empty box".
Note also that a: is the same:
a:
┌┐
││
└┘
a: -: <}.1
1
(Finally, I should perhaps note that I have no idea what problem you
are giving up on. Usually, though, "academic exercises" - which
typically focus more on how the goal is reached than on reaching the
goal - tend to feel forced in J.)
Thanks,
--
Raul
On Wed, Jun 7, 2017 at 1:03 PM, Michael Rice <[email protected]> wrote:
@robert therriault
my_empty =: }. 1
my_empty
f my_empty
1
< my_empty
┌┐
││
└┘
An empty box?
I'm beginning to see the problem I was thinking of doing in J is
ill-suited
to the language. It could be done, as it could in any computer language,
but the solution would be pretty kludgy.
I'll soon think of something else on which to apply J. It's already
invading my sleep. Going through exercises is no way to get into a
language. One needs a problem on which to focus it. I've been wanting to
explore cryptography more deeply, and J seems ideal for it.
Thanks to all,
Michael
On Wed, Jun 7, 2017 at 12:01 PM, robert therriault <
[email protected]>
wrote:
I'm going to look at these results through the lens of Shape ($)
f =: (1&,)
f 2
1 2
$ f 2 NB. shape is 2
2
f ''
1
$ f '' NB. shape is 1
1
empty NB. it is a verb in my environment
(i.0 0)"_
f empty
f empty NB. result of two verbs and no arguments is just the two verbs
f empty 2 NB. this is where you expect to have a 1 returned
$ f empty 2 NB. shape is 1 0
1 0 NB. one line of no items means no display
I think it is the second dimension of EMPTY as opposed to NULL that is
tripping you up.
NULL=.''
$ NULL
0
EMPTY
$EMPTY
0 0
EMPTY-:empty 1
1
In answer to your most recent question Michael, I would say just make
sure
that the empty list that you pass is the right shape.
Cheers, bob
On Jun 7, 2017, at 8:48 AM, Raul Miller <[email protected]>
wrote:
empty is a verb
f is a verb
so f empty is a verb (a hook)
f=: 1&,
(f empty) 3
$(f empty) 3
3 0
$(f empty) 5
5 0
The reasons for this are documented at
http://www.jsoftware.com/help/dictionary/dictf.htm (hooks) and
http://www.jsoftware.com/help/dictionary/d630n.htm (x m&v y).
That said, verbs take arguments and empty is a verb - it always
produces an empty result, but only when it gets an argument.
I hope this helps,
--
Raul
On Wed, Jun 7, 2017 at 11:39 AM, Michael Rice <[email protected]>
wrote:
Oops! Guess I creamed empty. Will close and regen Jqt before
proceeding.
Done!
f =: (1&,)
f 2
1 2
f empty
f empty
Shouldn't it have returned
1
?
On Wed, Jun 7, 2017 at 11:22 AM, robert therriault <
[email protected]>
wrote:
One thing to remember is that empty is already defined as a verb
empty
(i.0 0)"_
So if you overwrite this you may break some code if you have
previously
relied on the existing verb definition.
I think along the lines that Pascal mentioned that null could be
similarly
defined as
null NB. check that it is not already used
|value error: null
null=:(i.0)"_
NULL NB. check that it is not already used - uppercase for global
nouns is a convention I like and is often seen in J code
|value error: NULL
NULL=:'' NB. I use this as the null string (same as what John
suggested)
NULL-:null 2 NB. any argument produces NULL from null
1
Hope this helps,
Cheers, bob
On Jun 7, 2017, at 8:09 AM, 'Jon Hough' via Programming <
[email protected]> wrote:
I may be wrong in doing this, but I usually write
empty=: ''
to signify an empty list, array, matrix etc.
On Jun 7, 2017, 23:59, at 23:59, Michael Rice <[email protected]
wrote:
Is there a special "noun" for an empty list?
Creating one seems enigmatic.
empty =: 1 2
empty
1 2
empty =: }. empty
empty
2
empty =: }. empty
empty
empty1 =:
|syntax error
| empty1=:
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