6 ms·

I did look at wikipedia, yes, which gave me a page of type theory related stuff without any apparent grounding in practicalities, which gives the conclusion tha

by pm215 9y ago

I did look at wikipedia, yes, which gave me a page of type theory related stuff without any apparent grounding in practicalities, which gives the conclusion that it's apparently unimportant unless you particularly like mathematical theory. Yes, I could go and research functional programming languages and type theory; but my point is that if you're critiquing a blog post on a non-functional programming language then doing it in terms that only FP advocates will understand is missing the target audience.

kod 9y ago
What wikipedia page did you look at? This has plenty of practicality https://en.m.wikipedia.org/wiki/Sum_type https://en.m.wikipedia.org/wiki/Sum_type
- pm215 9y ago
  I was looking at https://en.wikipedia.org/wiki/Product_type https://en.wikipedia.org/wiki/Product_type FWIW.
tel 9y ago
Type theory isn't FP as much as logic--it applies everywhere. That said, totally agree that you're unlikely to have encountered it outside of an FP context in 2017. Product and sum type are fundamental structures for construction of information. A product of two pieces of information is a piece of information equivalent to having both at once: it's sort of like "and". A sum of two pieces of information is a piece of information equivalent to having exactly one or the other and knowing which of the two you have: it's sort of like "xor".
rbehrends 9y ago
A sum type `T = A | B` means that a value of type `T` can be either of type `A` or of type `B`. Such a type is used to express polymorphism. A product type (from "Cartesian product", i.e tuples) `T = A * B` means that a value of type `T` has a component that is of type `A` and another component that is of type `B`. It is used to aggregate parts into a whole. > Yes, I could go and research functional programming languages and type theory It has absolutely nothing to do with functional programming and touches only upon the barest essentials of type theory (and calling it type theory is already stretching it, because it's just about defining a couple of common computer science concepts). Sum and product types are fundamental computer science vocabulary to such an extent that it's not really possible to have a useful discussion about programming language semantics without them.
- vram22 9y ago
  >A sum type `T = A | B` means that a value of type `T` can be either of type `A` or of type `B`. Such a type is used to express polymorphism. Taking this example (in English / pseudocode): Define a class Animal. Define Dog as a subclass of Animal. Define Cat as a subclass of Animal. Case 1) Now if we have a variable a1 that can, at runtime, contain (or refer to) either a Dog or an Animal instance. Case 2) And if we have a variable a2 that can, at runtime, contain (or refer to) either a Dog or a Cat instance. Referring to your quoted sentences above, would you say that Case 1, Case 2 or both, are about sum types? Just trying to understand the terminology.
  - rbehrends 9y ago
    Both. Assuming that you can actually exclude instances of class Cat in case 1 and of Animal in case 2, that is. In case 1, the actual type of a1 would be Animal | Dog. In case 2, the actual type of a2 would be Dog | Cat. (Either a1 or a2 might be declared with a different type, this is about the values that they can actually hold, according to your stated premises.)
    - vram22 9y ago
      >Both. Assuming that you can actually exclude instances of class Cat in case 1 and of Animal in case 2, that is. Good point. I was actually thinking in terms of Python OOP, and in that, you cannot exclude those instances (at least not without some extra code).
  - leshow 9y ago
    I'm not sure if you can really express it in OO. Sum types are used to represent a closed set of variants. Inheritance like that isn't closed. In languages that have both OO and ML/Haskell-style type systems like Scala, the fact that the set is closed is denoted by the keyword 'sealed'. example sealed trait Color final case object Red extends Color final case object Green extends Color Color can only be Red OR Green. In your example you can have an Animal, a Dog, a Cat, and other things can inherit Animal and create more variants.
deleted 9y ago
[deleted]
empath75 9y ago
A practical example is a function that can return either a value or an error. Those are two different types that are combined into a Sum type called a Result. When you write some code that handles results, you need to account for both possible outcomes or you'll get a compiler error (or a panic). A product type is basically an object where you have a person type which in includes attributes like 'Name', 'Age', etc.
nine_k 9y ago
Remember when you first encountered some seemingly hard topic early in your developer's life. Pointers? Virtual functions? Futures? Pick something from your experience on what you had to spend a couple of weeks to get a grasp. Now think: * Was it useful? * Is it hard, from your current perspective? Ponder.

by pm215 9y ago

kod 9y ago

What wikipedia page did you look at? This has plenty of practicality https://en.m.wikipedia.org/wiki/Sum_type https://en.m.wikipedia.org/wiki/Sum_type

pm215 9y ago
I was looking at https://en.wikipedia.org/wiki/Product_type https://en.wikipedia.org/wiki/Product_type FWIW.

tel 9y ago

Type theory isn't FP as much as logic--it applies everywhere. That said, totally agree that you're unlikely to have encountered it outside of an FP context in 2017. Product and sum type are fundamental structures for construction of information. A product of two pieces of information is a piece of information equivalent to having both at once: it's sort of like "and". A sum of two pieces of information is a piece of information equivalent to having exactly one or the other and knowing which of the two you have: it's sort of like "xor".

rbehrends 9y ago

A sum type `T = A | B` means that a value of type `T` can be either of type `A` or of type `B`. Such a type is used to express polymorphism. A product type (from "Cartesian product", i.e tuples) `T = A * B` means that a value of type `T` has a component that is of type `A` and another component that is of type `B`. It is used to aggregate parts into a whole. > Yes, I could go and research functional programming languages and type theory It has absolutely nothing to do with functional programming and touches only upon the barest essentials of type theory (and calling it type theory is already stretching it, because it's just about defining a couple of common computer science concepts). Sum and product types are fundamental computer science vocabulary to such an extent that it's not really possible to have a useful discussion about programming language semantics without them.

vram22 9y ago
>A sum type `T = A | B` means that a value of type `T` can be either of type `A` or of type `B`. Such a type is used to express polymorphism. Taking this example (in English / pseudocode): Define a class Animal. Define Dog as a subclass of Animal. Define Cat as a subclass of Animal. Case 1) Now if we have a variable a1 that can, at runtime, contain (or refer to) either a Dog or an Animal instance. Case 2) And if we have a variable a2 that can, at runtime, contain (or refer to) either a Dog or a Cat instance. Referring to your quoted sentences above, would you say that Case 1, Case 2 or both, are about sum types? Just trying to understand the terminology.
- rbehrends 9y ago
  Both. Assuming that you can actually exclude instances of class Cat in case 1 and of Animal in case 2, that is. In case 1, the actual type of a1 would be Animal | Dog. In case 2, the actual type of a2 would be Dog | Cat. (Either a1 or a2 might be declared with a different type, this is about the values that they can actually hold, according to your stated premises.)
  - vram22 9y ago
    >Both. Assuming that you can actually exclude instances of class Cat in case 1 and of Animal in case 2, that is. Good point. I was actually thinking in terms of Python OOP, and in that, you cannot exclude those instances (at least not without some extra code).
- leshow 9y ago
  I'm not sure if you can really express it in OO. Sum types are used to represent a closed set of variants. Inheritance like that isn't closed. In languages that have both OO and ML/Haskell-style type systems like Scala, the fact that the set is closed is denoted by the keyword 'sealed'. example sealed trait Color final case object Red extends Color final case object Green extends Color Color can only be Red OR Green. In your example you can have an Animal, a Dog, a Cat, and other things can inherit Animal and create more variants.

deleted 9y ago

[deleted]

empath75 9y ago

A practical example is a function that can return either a value or an error. Those are two different types that are combined into a Sum type called a Result. When you write some code that handles results, you need to account for both possible outcomes or you'll get a compiler error (or a panic). A product type is basically an object where you have a person type which in includes attributes like 'Name', 'Age', etc.

nine_k 9y ago

Remember when you first encountered some seemingly hard topic early in your developer's life. Pointers? Virtual functions? Futures? Pick something from your experience on what you had to spend a couple of weeks to get a grasp. Now think: * Was it useful? * Is it hard, from your current perspective? Ponder.