That 2 ?. 8 is 2 4 is an accident. It doesn't explain why or how ?. works.
For instance, ([ , %~) is another verb that gives 2 4 from 2 f 8; I'm sure
imagination can supply others. The random number is not guaranteed to
generate any result in particular across versions; only, within a given
version, it is stable. What is important about ?. is that it generates random
numbers, and that the stream is the same for all invocations.
On Tue, 9 Aug 2022, Henry Rich wrote:
Thanks to you, Hauke, Don for the comments.
The Glossary has links to definitions.
We made the decision that !&| would be better known that the standard
math symbols
Certain special combinations ARE shown; which ones would you like?
2 ?. 8 is 2 4. What's wrong with that?
The Re and Im are a standard math notation.
The formulas is for the Moore-Penrose inverse, which is what %. y computes
If you want a simpler card, make one!
Henry Rich
On 8/9/2022 5:28 PM, Elijah Stone wrote:
It claims that x|y is x mod y, but it is in fact y mod x.
I don't think an example result of 2 4 for ?. is helpful.
In 'scalar dyadic verbs', why is footnote b attached to 'rnd', but
footnote c is attached to '?.'? They should be consistent.
I think that instead of 'Rank of ?. _, others 0', it should be 'Rank 0
(except ?.)'. Begin with the common case, then list exceptions.
The way the words 'Shape, Length, Rank' are spaced makes it look like
they are labels for the columns of the table they accompany. I don't
know what the solution is; it might be a good idea to left-align the
table headings, or possibly tighten the horizontal spacing.
The vertical spacing, on the other hand, is too tight; it makes the
tables difficult to scan. I would loosen it, even if it requires
adding a third page.
Names of standard library functions (datatype, load, etc.) don't link
anywhere.
'r. π' should presumably be 'r. 1p1', as it is meant to be a j sentence?
Maybe it helps somebody, but I find the colouration on the second
page--in particular for modifier trains and conjunctions--too busy; I
would mute it a bit. But this is a matter of taste.
For @., rather than '[x] Vn y' with a footnote to explain what n is, I
would say '[x] Vn y [ n=. [x] v y'. I would also use subscripts for
0, 1, and n. And I would replace n with i, since n is conventionally
used to name an argument to a conjunction.
u::v needs a space after u. I suggest that it should be stylised 'u .
v', not 'u .v' (and analogously for other conjunctions that start with
inflections).
'[x] u^:v y' is '[x] u^:([x] v y) y', which is not what the reference
says. Perhaps there should be a second row giving the common case of v
as a predicate.
In 'apply [x&]u til x&u y false', the second 'x&' needs to be
bracketed as optional.
In place of '[x&]u ...(n times) y', I would say '[x] u [x] u ...(n
times) y'. I don't think the & is helpful, and and showing multiple
instances of u makes it clearer exactly what it is that is happening n
times.
In the 'sort and grade' section, for a moment, I thought 'abcd' was
intended as a left argument to all the verbs. I guess this is because
it is the middle-most item. Maybe simply reordering would fix it.
Perhaps move /:@/: up above the sorts, together with the grades. Then
'abcd' is no longer in the middle, and /:~ has pride of place as the
last row (since it is likely to be the most common use of /: et co).
In 'atomic compound forms a?b', it looks like there is an application
of the verb ?. I would at the least italicise it rather than bolding it.
I am curious where the convention of using black capital letters R and
I to indicate the real and imaginary parts of a complex number comes
from.
On Tue, 9 Aug 2022, Henry Rich wrote:
Viktor Grigorov has a draft version of the new J Reference Card.
Please criticize it.
The source for the card is a LaTeX document, and will be freely
available for editing.
A PDF version is at
https://drive.google.com/file/d/1bpyfmksD-XEJaJJ972jOy3b2_KWfV0Wi/view?usp=sharing
Henry Rich
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