Questions tagged [type-systems]

a type system is a collection of rules that assign a property called a type to the various constructs—such as variables, expressions, functions or modules— that a computer program is composed of.

Filter by
Sorted by
Tagged with
12
votes
4answers
2k views

How do existential types differ from interfaces?

Given the existential type T = ∃X.{op₁:X, op₂:X→boolean} and this generic Java interface: interface T<X> { X op₁(); boolean op₂(X something); } What are the fundamental differences ...
31
votes
8answers
7k views

What's the tradeoff for type inference?

It seems that all new programming languages or at least the ones that became popular use type inference. Even Javascript got types and type inference though various implementations (Acscript, ...
1
vote
2answers
2k views

What exactly is a P-type software

I find this concept hard to understand. So in what situations we have solutions that are impractical or impossible like those P-systems try to implement? P-systems are described as: P-type [...
-1
votes
1answer
56 views

Appropriate base type for simply typed lambda calculus

Given the following hypothetical programming language: Intended for practical programming A simply typed lambda calculus (STLC) All objects are functions, based on Church encodings I am aware that ...
2
votes
3answers
183 views

Where is the boundary between things which can be statically typechecked, and those which must be typechecked dynamically?

I am brain storming on how to create a type system for a programming language, and what the compiler will do with the typing information. Here is what I have found, followed by the main question, ...
9
votes
6answers
851 views

Do any programming languages use types as values? Would there be any point?

The standard way that types are handled in programming languages that have such a concept, is that they are: removed entirely at compile time and are just used to determine memory layout, function ...
6
votes
3answers
603 views

Naming of union and intersection types in TypeScript

In TypeScript, the following is called a union type: number | string and this is called an intersection type: number & string However, is the resulting type of the | not actually an intersection,...
0
votes
1answer
55 views

What are the problems of subtyping?

I've heard often that Subtyping breaks some important and useful properties: many nice innovations developed by pure programming language researchers can't be brought to Java or C++ because of ...
1
vote
0answers
56 views

Using ftype to Declare Functions in Common Lisp

The Common Lisp Cookbook discusses how to use ftype to declare the inputs and outputs of functions. In compilers with a lot of type inferencing like SBCL, this would seem to offer a lot of support ...
4
votes
3answers
271 views

Verbose Return Types

I've recently been writing some code that deals with 3rd parties -- obviously errors will happen so I'm using Either/Maybe monads where appropriate. As this is C# I'm also using async Tasks too. My ...
2
votes
2answers
470 views

How are dynamic and static typings implemented?

As I understand, every programming language is either statically type checked or dynamically type checked (and there are cases where these two approaches are mixed, but for simplicity I won't mention ...
4
votes
1answer
1k views

When writing an interpreter, how should the type inference algorithm change the parsed AST? Should it?

When writing an interpreter, how should the type inference algorithm change the parsed AST? Should it? Or parsing and inference are done necessarily simultaneously? I have implemented a strongly typed ...
41
votes
6answers
9k views

Why is type inference useful?

I read code way more often than I write code, and I'm assuming that most of the programmers working on industrial software do this. The advantage of type inference I assume is less verbosity and less ...
4
votes
3answers
353 views

Liskov substitution for voids and weakened preconditions

I am learning a lot about this principle (also thanks to two answers I received here) and would like to elaborate on another point that somebody mentioned. 1) Is the following a violation of LSP? ...
0
votes
1answer
94 views

What are the benefits of not checking function arguments in python?

I'm trying to understand what are the benefits of the fact that python defaults to not checking function arguments. For example: from some_module import my_function my_function(some_argument) # ...
15
votes
2answers
2k views

Correct terminology in type theory: types, type constructors, kinds/sorts and values

In an answer to a previous question, a small debate started about correct terminology for certain constructs. As I did not find a question (other than this or that, which is not quite the right thing) ...
1
vote
1answer
110 views

How to avoid code duplication from handling “structually similar types” in Scala?

Often, when programming, you'll have different degrees of information to you in different contexts. For example, a web server may have two routes, which recieve information about a Person, one of ...
0
votes
2answers
221 views

Liskov substitution principle: clarification about the “history rule”

I`m trying to understand the LSP History rule. I have read Wikipedia entry which states the requirement and provides an example: History constraint (the "history rule"). Objects are regarded as ...
7
votes
3answers
4k views

Is there a practical use for dependent types?

I've been reading about this thing called dependent types. So for example imagine a function firstNPrimes(int n) which returns an array of length n. In other words the type it returned would be int[...
0
votes
1answer
101 views

What's the name of the technique of using very specific types to help catch errors?

By way of background, I recently coded a small app that detects the number of boxes in an image. The app defines some types, for example: class Box(val x1: Int, val y1: Int, val x2: Int, val y2: Int) ...
3
votes
2answers
163 views

Should entities have nullable id because they're autoganerated by the database?

Suppose I have a domain entity representing a person. (Examples in TypeScript) class Person { constructor(public name: string) {} } Now, because other parts of the domain will need to reference ...
18
votes
3answers
3k views

How do the type systems in functional languages differ from those in OO languages? [duplicate]

I keep reading stories from developers who state that once they are able to get the FP programs written in languages like Haskell, Ocaml, Elm and even Rust, to compile without errors, they are pretty ...
1
vote
0answers
111 views

What to do about compilation errors if ignoring them makes the app run fine?

Updating the libraries in my Angular 8/Electron app produced compilations errors eg, in Electron's menu.ts file, Also, a few of the project external libraries contain @ts-ignore lines, suppressing ...
1
vote
1answer
105 views

When is it a good idea to include explicit type declarations in Kotlin?

In Kotlin, specifying the return types of functions and the types of variables is usually optional but can be optionally included. I've encountered a few benefits of including them: It sometimes ...
1
vote
0answers
44 views

What is the advantage to inferred types *in Swift*? [duplicate]

As I fool around in Swift I have come to absolutely hate variable declarations. int c = 0 seems easier to read than var c:Int = 0 and more informative than var c = 0, and int some() is radically ...
28
votes
7answers
8k views

Is hungarian notation a workaround for languages with insufficiently-expressive static typing? [closed]

In Eric Lippert's article What's Up With Hungarian Notation?, he states that the purpose of Hungarian Notation (the good kind) is to extend the concept of "type" to encompass semantic information ...
5
votes
3answers
260 views

Is checking for unexpected types in dynamic languages in an untyped project necessary?

In statically typed languages or dynamically typed languages that use a type checking system you can guarantee that the input type is the type that you specified in the contract. However, in ...
0
votes
1answer
774 views

Difference between a strongly typed language and a weakly typed language with type annotations from the developer's point of view?

I understand that there are major technical differences between how a strongly typed language is compiled and how a type annotated language is compiled/transpiled. But as a developer writing in a ...
51
votes
8answers
9k views

Is there a reason to have a bottom type in a programming language?

A bottom type is a construct primarily appearing in mathematical type theory. It is also called the empty type. It is a type that has no values, but is a subtype of all types. If a function's return ...
72
votes
7answers
8k views

Dynamically vs Statically typed languages studies [closed]

Do there exist studies done on the effectiveness of statically vs dynamically typed languages? In particular: Measurements of programmer productivity Defect Rate Also including the effects of ...
15
votes
2answers
2k views

(Dis-)advantages of structural typing

I’ve just watched this talk by Daniel Spiewak where he talks about the advantages of structural typing as compared to Scala’s ans Java’s nominal typing. One example for this difference would be the ...
45
votes
5answers
17k views

Why does Java not do type inference?

I have always wondered why Java does not do type inference given that the language is what it is, and its VM is very mature. Google's Go is an example of a language with excellent type inference and ...
1
vote
2answers
320 views

Best practice regarding interfaces between “typed” and untyped" languages?

Our frontend JavaScript / Vue code makes uses of a number of "internal" REST endpoints, which are implemented in Java using Jersey/jax-rs. We have an "informal" specification that lists the ...
58
votes
16answers
12k views

How should I store “unknown” and “missing” values in a variable, while still retaining the difference between “unknown” and “missing”?

Consider this an "academic" question. I have been wondering about about avoiding NULLs from time to time and this is an example where I can't come up with a satisfactory solution. Let's assume I ...
29
votes
8answers
6k views

Using a “strong” type system in the real world, say, for large-scale web-apps?

I know this is a very broad, ambiguous, and possibly philosophical question. To an extent, that the most important keyword in the question - "strong" type system - itself, is ill-defined. So, let me ...
-1
votes
1answer
90 views

How to develop larger client-site in-browser apps in javascript?

I'm new to javascript environment (I have background in C++ physical simulations and game engines). With rise of HTML5 and WebGL I was thinking I'd like to try make some games/3D editors using ...
0
votes
1answer
73 views

Implicit conversion for function subtyping

Languages with coercions (i.e. implicit type conversions) allows expressing things like that (irrespective of any syntax): f : int32 → int32 = λx.x+x a : int16 = 42 b : int64 = f(a) Where type ...
10
votes
4answers
539 views

How exactly does a compiler recover from a type error?

I've read several papers, articles, and section 4.1.4, chapter 4 of Compilers: Principles, Techniques, and Tools (2nd Edition) (a.k.a "The Dragon Book") which all discuss the topic of syntactical ...
3
votes
2answers
500 views

Representing a structure/tuple type with Hindley Milner Type Inference

I'm writing a really simple interpreted object oriented programming language with a C-like syntax. I've been looking into type inference and I've found a few implementations of the 'Hindley-Milner ...
0
votes
4answers
400 views

type infered statically typed languages?

are there any typeless typesafe languages? By typesafe I mean types are checked at compile time. By typeless I mean types are not declared. I know this is easier than it sounds, maybe even impossible ...
3
votes
2answers
126 views

What's the best way to store class/type info in a plugin system in your software?

There are lots of applications like 3ds Max, Maya, etc that allows you to use plugins, where even the default nodes are created as plugins. This is all good but if the developer changes the class/...
4
votes
2answers
798 views

Argument contravariance, real world purpose and usage?

I have read a few questions on the SO and elsewhere and still do not understand well where this "widening" of a parameter type can be helpful, i.e. compliying to Liskov substitution principle. The ...
1
vote
0answers
109 views

Can machine learning be used for non-numerical prediction?

I've started reading a machine learning book since a few days ago, and I've learned about how it can be used for classification/regression/etc. However, I am unsure if it will be able to handle the ...
2
votes
1answer
162 views

What is the term for different types that contain the same information?

What is the correct term(s) for different types that contain exactly the same information? For example (F#): type Type1 = (int * string) type Type2 = (string * int) When describing that these types ...
56
votes
14answers
7k views

When is type testing OK?

Assuming a language with some inherent type safety (e.g., not JavaScript): Given a method that accepts a SuperType, we know that in most cases wherein we might be tempted to perform type testing to ...
0
votes
1answer
315 views

TypeScript - Can “Structural typing” and “OOP paradigm” co-exist?

From Type Compatibility - Introduction: Structural typing is a way of relating types based solely on their members. This is in contrast with nominal typing. Consider the following code: ...
17
votes
9answers
48k views

Should one test the values of an enum using unit tests?

If you have an enum with values only (no methods as one could do in Java), and this enum is part of the business definition of the system, should one write unit tests for it? I was thinking that they ...
1
vote
2answers
81 views

Why 'Package' type does not inherit 'AccessibleObject' type?

Below are the relevant types(in java) for annotation processing, In addition to Field & Method types, Package type is also used in context of annotations with reflection, because these types ...
11
votes
1answer
512 views

Using Haskell type classes to enforce commutativity

I want to define a type class for geometric objects that can be intersected together: class Intersect a b c | a b -> c where intersect :: a -> b -> c -- Language extensions: -...
30
votes
9answers
4k views

Are there any design patterns that are possible only in dynamically typed languages like Python?

I've read a related question Are there any design patterns that are unnecessary in dynamic languages like Python? and remembered this quote on Wikiquote.org The wonderful thing about dynamic typing ...