The verb form u} is still supported. It doesn't fit in well with the
rest of u} as currently defined, which is why I deprecated it. I think
if Ken designed the language anew he might define u} differently.
(x u y) calculates a set of atom numbers (each a single number giving
the position of a modificand atom in ,y). Atoms of x are stored at
those numbers. Calculating the atom numbers is expensive for arrays of
rank>1, and modifying a cell larger than an atom requires addressing
each atom individually. m} is faster and easier.
Henry Rich
On 7/1/2019 11:41 PM, Daniel Eklund wrote:
I have been working my way through the "Learning J" online book
https://www.jsoftware.com/help/learning/contents.htm
with a recency of 2015.
In the 6th chapter (https://www.jsoftware.com/help/learning/06.htm) there
is a sub-section dedicated to using bare verbs (not gerunds) as the bound
left conjunct to Amend (with explanations of linear-indices).
Later, in the 14th chapter (14.3.5 Gerund as Argument to Amend) gerunds are
introduced as viable tied-nouns to be the bound left conjunct to Amend.
Additionally, the NuVoc for Amend has (all the way at the bottom) a warning
as follows:
"An obsolete form of Amend: (x u} y) was used in early versions of J.
where operand u is a verb. Its use is deprecated in favor of x m} y."
Is it true to say that this warning refers to the same verbs as discussed
in Chapter 6?
thanks
Daniel Eklund
PS. It took me a bunch of searching through nabble to find the gerund
usage of Amend as a means (preferable, in my opinion) to dynamically
generate indices and replacement values in a nice calculable way (
http://jsoftware.2058.n7.nabble.com/Tacit-definition-using-Amend-td4950.html#a4951).
which led me to search ahead to Chapter 14 to discover the gerund form.
I say this in the context of me being a complete newbie and struggling to
use Amend with calculated indices in various programming exercises. I hope
not to sound critical.
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