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.

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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 ...
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Should an interface covariant on T ever implement an interface invariant on it?

I was reading through the Hacklang docs on Collections, and came across this curious definition [paraphrased slightly]: interface KeyedIterable<Tk, Tv> ... interface ConstVector<+Tv> ...
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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 ...
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Which statically typed languages support intersection types for function return values?

Initial note: This question got closed after several edits because I lacked the proper terminology to state accurately what I was looking for. Sam Tobin-Hochstadt then posted a comment which made ...
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Type of multi methods in a static object-functional language

I'm currently working on expanding the capabilities of my pet programming language project's type system, and have come across an interesting area where my research into other language's type systems ...
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What does the “t” in int32_t signify?

In C, what meaning, if any does the t at the end of integer types like uint8_t and int32_t have? Where did it originate? Why wasn't the type just called int32?
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Perform crossover operation on AST in genetic programming

So in general when you perform a crossover in GA, you directly flip a random section in the "genome", with the corresponding section in the other parent, and mutate it based on the mutation rate. ...
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Could Hindley-Milner inference work for the Go language?

I've read that Hindley-Milner does not work with type systems that have subclasses, and there are other type system features that also do not work well with it. Go currently has only very limited type ...
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Duck checker in Python: does one exist?

Python uses duck-typing, rather than static type checking. But many of the same concerns ultimately apply: does an object have the desired methods and attributes? Do those attributes have valid, in-...
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What does weak static typing/strong dynamic typing mean?

For most of my career, I've been working with strong static typed languaged such as Java. For this reason, probably I've mixed up these two typing dimension (strongness and staticness). I came upon ...
18
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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, ...
65
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5answers
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Is Haskell's type system formally equivalent to Java's? [closed]

I realize some things are easier/harder in one language than the other, but I'm only interested in type-related features that are possible in one and impossible/irrelevant in the other. To make it ...
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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 ...
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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 ...
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2answers
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Why (or why not) are existential types considered bad practice in functional programming?

What are some techniques I might use to consistently refactor code removing the reliance on existential types? Typically these are used to disqualify undesired constructions of your type as well as to ...
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2answers
884 views

Is it possible to “bake dimension into a type” in haskell?

Suppose I want to write a library that deals with vectors and matrices. Is it possible to bake the dimensions into the types, so that operations of incompatible dimensions generate an error at compile ...
3
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1answer
367 views

What do banks actually use as a data type for money? [closed]

I'm aware of a few good options: Big integers (e.g., int64_t, mpz_t, any bignum lib) to represent cents or 10-n cents—say, an integer represents 1/100 of a penny ($1.05 == 10500). This is called a ...
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1answer
240 views

Why covariance is forbidden for abstract class in C#

I've been digging in covariance and contravariance in C# and there is one thing I could not manage to understand. C# (AFAIK, as of 4 version) allows one to declare the covariant or contravariant ...
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7answers
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Type casting variables in PHP, what is the practical reason for doing this?

PHP, as most of us know, has weak typing. For those who don't, PHP.net says: PHP does not require (or support) explicit type definition in variable declaration; a variable's type is determined ...
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2answers
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Why are semantics and type systems are so important?

I heard that semantics and type systems are very important for all programmers! But I why are they so important? I don't understand. Maybe they are imortant only for theoreticians and compiler ...
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1answer
229 views

How can a object have many types?

I am currently reading Design Patterns - Elements of Reusable Object-Oriented Software. I am in chapter 1 at page 16 in section Class versus Interface Inheritance. There in the last line of the page ...
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2answers
192 views

Haskell types for functions

I don't understand the answer to this question: Q: Can Haskell find a type for the function selfapply defined by: selfapply f = f f A: The function selfapply is not typeable in the simple ...
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How do languages with Maybe types instead of nulls handle edge conditions?

Eric Lippert made a very interesting point in his discussion of why C# uses a null rather than a Maybe<T> type: Consistency of the type system is important; can we always know that a non-...
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2answers
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Is there a name for this in type theory? Specify that a value satisfies multiple interfaces without specifying the concrete type

I have often wanted the same feature which is asked for e.g. here and in many other questions on SO: Being able to specify that something satisfies multiple interfaces without specifying the ...
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3answers
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Should conditional logic be always coded via type system where possible?

I have a choice. Option 1: public class Sample { bool IsRelevant { get; set; } } Option 2: public class Sample { } public class RelevantSample : Sample { } Is there a clear well-known rule ...
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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 ...
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Why is behavorial subtyping undecidable?

Liskov's work in this area focused on behavioral subtyping, which besides the type system safety discussed in this article also requires that subtypes preserve all invariants guaranteed by the ...
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Confusion about data types, compilers, hardware data representation and static vs dynamic typing [closed]

I am trying to understand static vs dynamic typing, but am really struggling to see how everything fits together. It all starts with data types. As far as I understand, data types are quite abstract ...
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2answers
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Is there any practical use for the empty type in Common Lisp?

The Common Lisp spec states that nil is the name of the empty type, but I've never found any situation in Common Lisp where I felt like the empty type was useful/necessary. Is it there just for ...
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2answers
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Can there be value types in dynamic languages? [closed]

A value type is one whose instances are themselves saved in variables. A reference type is a type whose instances are saved somewhere and variables only hold the addresses of the instances. Some ...
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A secondary “type system” for references?

I'm designing a language and was wondering how to incorporate C++-like references with regards to their place in the type system. I think they're useful for operations like indexing and dereferencing (...
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3answers
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Banning zero-argument functions — what problems could it cause in a hypothetical language?

I'm creating a programming language as a hobby, but I encountered a problem with designing its syntax. The problem is the conflict between the syntax for defining zero-argument functions and the ...
4
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1answer
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Lambda Return Type Inference

Writing my own JVM compiler, I am facing a giant problem that I am desperately unable to solve: Lambda Return Type Inference 1. Overview of the compiler lifecycle More specifically, the order in ...
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1answer
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With sufficiently advanced static typing, what are the advantages of dynamic type systems? [closed]

This question appears to be fairly well tread, for example: Do dynamic typed languages deserve all the criticism? What is the supposed productivity gain of dynamic typing? etc. However, most ...
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Using uniqueness types to implement safe parallelism

I've been interested in uniqueness types as an alternative to monads in pure functional languages for some time; unfortunately, this is kind of an esoteric area of CS research and online resources ...
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2answers
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Are static methods of a class part of its type?

As far as I understand it, classes –as they are supported in OOP languages such as C++, Java, and Scala – define the type of each object I can instantiate with that class. Not all features of a class ...
32
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Is Haskell's type system an obstacle to understanding functional programming? [closed]

I'm studying Haskell for the purpose of understanding functional programming, with the expectation that I'll apply the insight that I gain in other languages (Groovy, Python, JavaScript mainly.) I ...
119
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10answers
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Should we define types for everything?

Recently I got into a problem with the readability of my code. I had a function that did an operation and returned a string representing the ID of this operation for future reference (a bit like ...
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1answer
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Why is Haskell unable to avoid repeated evaluation without the monomorphism restriction?

I just finished learnyouahaskell the other day, and I was trying to make sense of the Monomorphism Restriction, as described by the Haskell Wiki. I think I understand how the MR can prevent repeated ...
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What do you get when you cross a multi-precision integer with a floating-point number?

I'm working on adding multi-precision integers to the suite of numeric types in my APL interpreter, but I'm not sure what to do about the odd type-combinations that now arise. I now have the following ...
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Is there a difference between casting and converting types in imperative programming languages?

The question came up in a discussion at StackOverflow. Is there a clean distinction between the two concepts cast and convert (concerning the type of an object), or are these two words describing ...
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1answer
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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/...
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Is higher-rank parametric polymorphism useful?

I'm pretty sure everyone is familiar with generic methods of the form: T DoSomething<T>(T item) This function is also called parametrically polymorphic (PP), specifically rank-1 PP. Let's ...
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What are the safety benefits of a type system?

In JavaScript: The Good Parts by Douglas Crockford, he mentions in his inheritance chapter, The other benefit of classical inheritance is that it includes the specification of a system of types. ...
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1answer
541 views

Why do you need higher kinds?

Some languages allow for classes and functions with type parameters (such as List<T> where T may be an arbitrary type). For example, you can have a function like: List<S> Function<S, T&...
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What is the reason of using an interface versus a generically constrained type

In object-oriented languages that support generic type parameters (also known as class templates, and parametric polymorphism, though of course each name carries different connotations), it is often ...
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2answers
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how does test-driven development prevent us from type errors?

I heard (from Robert C. Martin) an assertion that since dynamic languages don't have static typechecking, people should write unit tests to prevent us from type errors. I'm not sure if I'm following ...
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Are single method interface and function type definition the same?

In a language where it is possible to define interfaces and typedefs (using Dart here): abstract class Receiver { void receive(int quantity); } typedef void Receive(int quantity); abstract class ...
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Managing types and conversions in a compiler

I am trying to determine how to manage types and conversions between types within a compiler that I am writing. The compiler is being written in C#. There are a number of different kinds of types. ...
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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: -...