Hi all!
This touches one of the most interesting aspects of J.
Variables in J are normally non-mutable in the sense that they can not
be modified in-place.
You can not set variable A to 1 2 3 and then change it to 1 3 without
creating a new variable, but one which might have the same name.
This means that the answer to question 1. is "There is no way to delete
an item from a list.". What you do is assigning the items you want to
remain in the list to a new variable.
So, why is this interesting?
In functional programming we usually work with non-mutable variables.
This means we can not even reassign a loop variable. Usually this means
we work recursively. There are also lots of other tricks we use to
transform one variable into another without doing it in small
increments. J is filled with such tricks. This means, as I see it, that
J should be interesting for functional programmers since it shows many
ways to transform a variable into another without changing the variable
incrementally.
Many APL/J tricks for this are now built into for example the array
class in F#. There is scan, fold and map, for example. But as far as I
know, many are still not widely used among other functional programmers.
Agreement and Rank are some examples.
PS. There are some exceptions when J variables are changed in-place. DS.
Cheers,
Erling Hellenäs
On 2017-12-03 18:40, Andrew Dabrowski wrote:
1. What's the idiomatic way to delete an item from a list? This
doesn't seem to come up in Learning J. For that matter, what's a good
reference for list slicing ops in J?
2. Is anyone bothered by the lack of a built-in associative list
structure? There are at least two different implementations in
Rosetta Code, but one is very bare-bones and the other uses classes,
which I'd prefer to avoid (I confess to having a bias against OO). I
guess J people have found other substitutes for
dicts/hashes/maps/associative arrays.
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