Programming Languages

1177 readers

1 users here now

Hello!

This is the current Lemmy equivalent of https://www.reddit.com/r/ProgrammingLanguages/.

The content and rules are the same here as they are over there. Taken directly from the /r/ProgrammingLanguages overview:

This community is dedicated to the theory, design and implementation of programming languages.

Be nice to each other. Flame wars and rants are not welcomed. Please also put some effort into your post.

This isn't the right place to ask questions such as "What language should I use for X", "what language should I learn", and "what's your favorite language". Such questions should be posted in /c/learn_programming or /c/programming.

This is the right place for posts like the following:

"Check out this new language I've been working on!"
"Here's a blog post on how I implemented static type checking into this compiler"
"I want to write a compiler, where do I start?"
"How does the Java compiler work? How does it handle forward declarations/imports/targeting multiple platforms/?"
"How should I test my compiler? How are other compilers and interpreters like gcc, Java, and python tested?"
"What are the pros/cons of ?"
"Compare and contrast vs. "
"Confused about the semantics of this language"
"Proceedings from PLDI / OOPSLA / ICFP / "

See /r/ProgrammingLanguages for specific examples

Related online communities

founded 1 year ago

MODERATORS

armchair_progamer

If Inheritance is so bad, why does everyone use it? (buttondown.email)

submitted 6 months ago by armchair_progamer to c/programming_languages

31 comments fedilink hide all child comments

This essay says that inheritance is harmful and if possible you should "ban inheritance completely". You see these arguments a lot, as well as things like "prefer composition to inheritance". A lot of these arguments argue that in practice inheritance has problems. But they don't preclude inheritance working in another context, maybe with a better language syntax. And it doesn't explain why inheritance became so popular in the first place. I want to explore what's fundamentally challenging about inheritance and why we all use it anyway.

you are viewing a single comment's thread
view the rest of the comments

[–] oessessnex 5 points 6 months ago (1 children)

The sum and product types follow pretty much the same algebraic laws as natural numbers if you take isomorphism as equality.

Also class inheritance allows adding behaviour to existing classes, so it's essentially a solution to the expression problem.

[–] onlinepersona 1 points 6 months ago (1 children)

Yes, I know some of those words. Could you repeat that for those that aren't mathematicians or in the know?

Anti Commercial-AI license

[–] oessessnex 1 points 6 months ago* (last edited 6 months ago)

As you already figured out the types are sets with a certain number of elements.

Two types are isomorphic if you can write a function that converts all elements of the first one into the elements of the second one and a function which does the reverse. You can then use this as the equality.

The types with the same number of elements are isomorphic, i.e True | False = Left | Right. For example, you can write a function that converts True to Left, False to Right, and a function that does the reverse.

Therefore you essentially only need types 0, 1, 2, 3, ..., where type 0 has 0 elements, type 1 has 1 element, etc. and all others are isomorphic to one of these.

Let's use (*) for the product and (+) for the sum, and letters for generic types. Then you can essentially manipulate types as natural numbers (the same laws hold, associativity, commutativity, identity elements, distributivity).

For example:

2 = 1 + 1 can be interpreted as Bool = True | False

2 * 1 = 2 can be interpreted as (Bool, Unit) = Bool

2 * x = x + x can be interpreted as (Bool, x) = This of x | That of x

o(x) = x + 1 can be interpreted as Option x = Some of x | None

l(x) = o(x * l(x)) = x * l(x) + 1 can be interpreted as List x = Option (x, List x)

l(x) = x * l(x) + 1 = x * (x * l(x) + 1) + 1 = x * x * l(x) + x + 1 = x * x * (l(x) + 1) + x + 1 = x * x * l(x) + x * x + x + 1 so a list is either empty, has 1 element or 2 elements, ... (if you keep substituting)

For the expression problem, read this paper: doi:10.1007/BFb0019443