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Generalised plusequals

15 points by leontrolski

by flebron

1 subcomments

The 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...).

by RodgerTheGreat

1 subcomments

In 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 dictionary. Lil's basic datatypes are immutable, so "l" is rebound to a new list containing a new dictionary, leaving any previous references undisturbed:
```
    l[1][1].age:9
    # (1,(2,{"age":9}),4)
    cat
    # {"age":3}
```
There's no special "infix" promotion syntax, so that last example would be:
```
    l:l,5
    # (1,(2,{"age":9}),4,5)
```
[0] http://beyondloom.com/tools/trylil.html

by rokob

0 subcomment

Yeah this looks like lenses at first glance

by hatthew

1 subcomments

It 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?

by beaumayns

0 subcomment

q 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.