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.

learn more… | top users | synonyms (1)

5
votes
3answers
151 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 ...
4
votes
2answers
61 views

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 ...
8
votes
1answer
156 views

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. ...
19
votes
1answer
1k views

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 ...
4
votes
1answer
110 views

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> ...
3
votes
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 ...
3
votes
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 ...
3
votes
1answer
230 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 ...
2
votes
2answers
218 views

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 ...
2
votes
2answers
174 views

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 ...
23
votes
8answers
4k 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 ...
12
votes
2answers
795 views

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 ...
2
votes
3answers
418 views

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 ...
0
votes
5answers
110 views

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 ...
0
votes
2answers
130 views

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 ...
3
votes
4answers
295 views

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 ...
1
vote
4answers
208 views

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 (...
3
votes
3answers
3k views

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
votes
4answers
786 views

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?
4
votes
1answer
292 views

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 ...
4
votes
1answer
183 views

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 ...
0
votes
2answers
93 views

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 ...
13
votes
1answer
265 views

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 ...
119
votes
10answers
9k views

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 ...
2
votes
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 ...
4
votes
2answers
138 views

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 ...
1
vote
1answer
59 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/...
39
votes
7answers
6k 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 ...
15
votes
2answers
504 views

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 ...
18
votes
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 ...
13
votes
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&...
14
votes
3answers
2k views

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 ...
0
votes
2answers
223 views

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 ...
2
votes
2answers
217 views

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 ...
18
votes
5answers
3k 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, ...
5
votes
0answers
170 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: -...
2
votes
1answer
94 views

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. ...
9
votes
5answers
2k views

class in OOP language and type

In programming language theory, a type is a set of values. E.g. the type "int" is the set of all integer values. In OOP languages, a class is a type, is it? When a class is defined with more than ...
27
votes
6answers
2k views

What are the caveats of implementing fundamental types (like int) as classes?

When designing and implenting an object-oriented programming language, at some point one must make a choice about implementing fundamental types (like int, float, double or equivalents) as classes or ...
1
vote
3answers
327 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 ...
7
votes
1answer
200 views

I'm being warned that the Monoid I'm creating is an Orphan Instance. Is there a better way to write this functionality in?

type PromptSegment = IO (Maybe String) instance Monoid a => Monoid (IO a) where mempty = return mempty mappend = liftA2 (<>) This behaves exactly how I want for my purposes. For ...
26
votes
3answers
2k views

A good generic type system

It's commonly accepted that Java generics failed in some important ways. The combination of wildcards and bounds led to some seriously unreadable code. However, when I look at other languages, I ...
3
votes
2answers
489 views

Is there a difference between duck typing and structural typing? [duplicate]

Duck typing is deciding on the type of an object, based on the operations it supports and the attributes it owns. Structural typing is... the same thing? What exactly is the difference?
6
votes
2answers
841 views

Alternative to language purity

Purity One of the interesting concepts in Haskell is the purity. However, I am wondering what the pragmatic reasons behind this is - let me explain a bit more before you reject my question. My main ...
3
votes
1answer
112 views

Is there a way to define a consistent date in a dependent type language?

I am looking for an example (if exists at all) of a definition of a date in a programming language (Idris, Coq, etc) that features dependent types where such definition is consistent and type safe by ...
22
votes
5answers
4k 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 ...
6
votes
2answers
323 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) ...
2
votes
3answers
267 views

Is 'design with types first' ultimately the same as 'design with interfaces first'?

In Object Oriented Programming, we're taught to think in terms of Polymorphism (the idea that the implementation is decoupled from the interface - and that it makes sense to think of the interface ...
1
vote
2answers
1k views

The Definition of “Strong Type Systems” [closed]

I saw Martin Odersky's "The Trouble with Types" presenstaion. He divided programing-languages in two dimensions in the "Type Systems Landscape" chart; A "Static/Dynamic" dimension and A "Strong/Weak" ...
3
votes
2answers
573 views

How does a dependently typed programming language cope with mutability?

I have been investigating on the viability of a "normal" programming language with dependent types. Think for example in Java and add dependent types to it. One difficulty which I have found is that ...