The J way is for x to be 'control information' and y to be 'data', so
that x u^:v y is intuitive.
Also, u/ processing is generally right to left through a cascade of items.
Also, x is optional. y can never be optional.
Putting those thoughts together, I came up with the current design.
Some agree, some have complained, but not stridently enough to convince
us to change it. Dissenters could get in the habit of writing (v~),
perhaps.
Henry Rich
On 7/2/2020 3:22 AM, Piet de Jong wrote:
Thanks. Didn’t realise the significance of the change. Have now got it to
work.
There is a feature of F:. which I find confusing.
The x argument to u F:. v appears to be the initial condition while the items
of y (I understand) are the items to be processed.
However insofar as v is concerned, the roles of x and y are reversed. That
is each y item becomes x for v as while the result of the previous
application of v is assumed to be y. Why this design?
Isn’t it more natural to think of the result of each iteration as the new
“initial condition.” (ie x) and the y for v as the next item to be processed
— ie the relevant item of y as passed to (u F:. v)
Having said that I find F:. an impressive addition.
On 2 Jul 2020, at 10:14 am, Henry Rich <[email protected]> wrote:
Fold changed in 9.02, reversing the meaning of u and v. You have 9.01 and are
expecting the old interpretation. NuVoc is for 9.02 (it has a note to that
effect IIRC).
Henry Rich
On 7/1/2020 7:29 PM, Piet de Jong wrote:
Started looking at fold — seems a very useful new verb.
However couldn’t get it to work
Engine: j901/j64avx2/darwin
Release-e: commercial/2020-01-29T12:41:32
Library: 9.01.21
Qt IDE: 1.8.6/5.12.7(5.12.7)
Platform: Darwin 64
Installer: J901 install
InstallPath: /applications/j901
Here is the what happens when I run the example from the vocabulary
u
3 : 0
z=. -y
z [smoutput ' u' ; y ; '-->' ; z
)
v
4 : 0
z=. y + 0.01
z [smoutput x ; 'v' ; y ; '-->' ; z
)
y
100 0.1 1.1 2.1 3.1
u F:.v y
|domain error
| u F:.v y
Any help much appreciated.
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