Generalised plusequals
leontrolski.github.io
Generalised plusequals
1–10 of 13 posts
Re: Generalised plusequals
#2The website asks what they do in Haskell. The answer is property modification and reading, as well as very powerful traversal constructs, use lenses (https://hackage.haskell.org/package/lens , tutorial at https://hackage.haskell.org/package/lens-tutorial-1.0.5/docs...).
Re: Generalised plusequals
#3Yeah this looks like lenses at first glance
Re: Generalised plusequals
#4It seems like this is proposing syntactic sugar to make mutating and non-mutating operations be on equal footing.
> The more interesting example is reassigning the deeply nested l to make the cat inside older, without mutating the original cat
Isn't that mutating l, though? If you're concerned about mutating cat, shouldn't you be concerned about mutating l?
Re: Generalised plusequals
#5It seems like this is proposing syntactic sugar to make mutating and non-mutating operations be on equal footing. > The more interesting example is reassigning the deeply nested l to make the cat inside older, without mutating the original cat Isn't that mutating l, though? If you're concerned about mutating cat, shouldn't you be concerned about mutating l?
It doesn't mutate l exactly, it makes a new list slightly different from the original one and assigns it to l.
That means if someone has a reference to the original l, they do not see the change (because l is immutable. Both of them).
Re: Generalised plusequals
#6q has the concept of amend, which is similar: https://code.kx.com/q4m3/6_Functions/#683-general-form-of-fu...
It's quite handy, though the syntax for it is rather clunky compared to the rest of the language in my opinion.
Re: Generalised plusequals
#7In Lil[0], this is how ordinary assignment syntax works. Implicitly defining a dictionary stored in a variable named "cat" with a field "age":
cat.age:3
# {"age":3}
l:1,(list 2,list cat),4
# (1,(2,{"age":3}),4)
l[1][1].age:9
# (1,(2,{"age":9}),4)
cat
# {"age":3}
l:l,5
# (1,(2,{"age":9}),4,5)
Re: Generalised plusequals
#8It seems like this is proposing syntactic sugar to make mutating and non-mutating operations be on equal footing. > The more interesting example is reassigning the deeply nested l to make the cat inside older, without mutating the original cat Isn't that mutating l, though? If you're concerned about mutating cat, shouldn't you be concerned about mutating l?
It doesn't mutate l exactly, it makes a new list slightly different from the original one and assigns it to l. That means if someone has a reference to the original l, they do not see the change (because l is immutable. Both of them).
[deleted]
Re: Generalised plusequals
#9It seems like this is proposing syntactic sugar to make mutating and non-mutating operations be on equal footing. > The more interesting example is reassigning the deeply nested l to make the cat inside older, without mutating the original cat Isn't that mutating l, though? If you're concerned about mutating cat, shouldn't you be concerned about mutating l?
It doesn't mutate l exactly, it makes a new list slightly different from the original one and assigns it to l. That means if someone has a reference to the original l, they do not see the change (because l is immutable. Both of them).
I think I am misunderstanding the behavior of the alt keyword
Re: Generalised plusequals
#10In Lil[0], this is how ordinary assignment syntax works. Implicitly defining a dictionary stored in a variable named "cat" with a field "age": cat.age:3 # {"age":3} Defining "l" as in the example in the article. We need the "list" operator to enlist nested values so that the "," operator doesn't concatenate them into a flat list: l:1,(list 2,list cat),4 # (1,(2,{"age":3}),4) Updating the "age" field in the nested dic…
This is surprising to me:
l[1][1].age:9
# (1,(2,{"age":9}),4)
{"age":9}
l_inner = l[1][1]
l_inner.age:9