Is Haskell dynamically typed ?

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Haskell is indeed a unique programming language due to its strong static system. The best way to have control over Haskell is to understand its design. Ideally, the system radically differs from dynamic programming languages such as Python, JavaScript, and Ruby. Interestingly, Haskell differs from other statistical languages like C++ and Java. 

Based on type systems, there are three categories of programming languages:

  1. No typing – these languages do not have a notion of types. The language has exactly one type. This is common in assembly languages as they only have the type “bit pattern,” and TK (Tcl) has on the type “Text,” and core MatLab features only the type ‘complex-valued matrix’.
  2. Weak typing – there are different types of types, though few. Again, developers can also use the several available type synonyms. This is common in programming languages like C. C uses integer numbers for Booleans, bit sets, characters, integers, and enumerations.
  3. Strong typing: these categories of programming languages features a fine set of types. This is prominent in languages like Ada, Wirth languages, e.g., Pascal & Modula-2, and Eiffel. Strong typing implies that variables lack Types, and the types within a language affect performing operations on a given variable. Strong typing requires that types be compatible with the operand while performing procedures. In dynamically typed languages like Python, a developer can add an integer and a floating-point number; however, adding an integer to strong results in error. 

Indeed understanding Haskell also involves understanding the fundamental difference between imperative programming and functional programming. While imperative programming developers give a program a series of commands, the developer’s code is simply an expression to be evaluated in functional programming. Haskell has a type system in which every expression has a type. Good thing; its compiler (GHC) is pretty good at type interface. It can determine each expression’s type in a code. 

Is Haskell dynamically typed
Is Haskell dynamically typed

Is Haskell dynamically or statically typed?

Haskell has static typing, making it a statically typed language. Static languages have types that are known at compile time. Haskell shares this feature with languages such as C/C++, Go, C#, Rust, Pascal, among others. 

Note that a statically typed programming language might or might not have a type interface. For instance, Java almost doesn’t have a type interface. By contrast, Haskell features an entire type interface.

A statically typed language might or might not have type inference. Java almost completely lacks type inference (but it’s very slowly changing just a little bit); Haskell has full type inference except for a few advanced extensions.

The unique thing about Haskell is that it provides a type – Dynamic that developers can safely use; however, this type is seldom needed. 

Dynamic vs. Static Typing

Type systems are essential for programming languages as they part of the advantages and disadvantages of the system. Static typing comes with several benefits – for instance, developers usually identify bugs at compile time instead of run time. This differs from dynamically typed languages, which identifies bug at run time. That means it’s possible to ship codes that seem to be working well but only run in problems later – causing the program to crash. 

For statistically typed languages, a code won’t run in the first place if it has a problem – errors are spotted when they occur. With statically typed languages, developers need a lot less time to test type agreements between methods. Besides, this a great thing in case developers is running an extensive library. 

Static type results in efficient codes – if the variable type is ‘ASCII character,’ the compiler understands that it must reserve a byte. So, a program won’t need to allocate memory for it during run time. 

The major shortcoming of statically typed languages like Haskell is that it takes much longer to complete the development of a code. So finding a solution in a dynamically typed language is much easier – for instance, you can do a database operation midway a pure code. In Haskell, this is an uphill task. 

Again, statically typed languages have more boilerplate code, which violates the DRY. Repeating the same code (boilerplate) across the classes is easy. However, if you want to change the codes, you might not remember all places you repeated the code. 

Object-oriented type systems offer a balancing act between static typing and dynamic typing. Each reference features a static type; however, developers can assign an object of a more specialized type to it at run time. Developers require type information and type checks at run-time. Nonetheless, performing static checks is essential. 

Haskell And Type Inference

As earlier stated, every expression has a type in Haskell. So, assigning types to expressions is not necessary for Haskell as is in C++ or Java. The compiler has sufficient information to perform the actions. But there is some consequence on the code syntax – all IF statements should have an else statement because every expression has a type. And, the result from both branches should have a similar type. Else, the compiler might not work correctly. 

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Why is Haskell called a lazy language?

Haskell features lazy evaluation – a feature that sets it apart from other programming languages. The main idea is that developers can only evaluate expressions when they need those expressions. This is the opposite of most other programming languages that implement Eager Evaluation

Eager evaluation means that an expression is evaluated in the instance that the program execution reaches an expression. This is particularly more sensible for imperative programming languages as they have a series of commands. Therefore, to flawlessly execute these commands, each expression is evaluated immediately. 

Though Haskell has a series of expressions to be evaluated, it works a little different here – Haskell has Lazy Evaluation. So, it will only evaluate those expressions it needs to generate a program output. Further, it only evaluates those expressions when it needs them instead of the moment it encounters them. 

Typically, when an evaluation engine spots an expression, it creates a thunk data structure containing the values it needs to evaluate the expression and a pointer to the expression. When the developer needs results, the evaluation engine calls the expression and replaces the thunk with future reference results.

A unique twist is; Haskell is also specified as Non-Strict, which is pretty much not similar to lazy evaluation. So, what does non-strict mean?

It simply means that reduction proceeds from outside to inside. Reduction is the mathematical term for evaluations. For instance, in the expression (a+(b*c)), reduce the + followed by the (b*c). for strict languages, the evaluations begin from the innermost brackets to the outer ones. 

These paradigms matter to the semantics because having an expression that evaluates to the bottom. Any language that begins at the inside and works outwards always finds the base value. Hence, the bottom propagates outwards. Contrarily, if you start from outside and work inwards, then eliminate some sub-expressions by outer reductions. This means they won’t be evaluated; thus, you won’t get “bottom.”

There is a strong correspondence between partly evaluated expression and thunk. As a result, the terms “lazy” and “non-strict” are synonyms in most cases. But there is a difference. 

Practically, Haskell isn’t a purely lazy language – for example, pattern matching is stringent. This forces evaluation to happen far enough to accept or reject a match. Besides, the strictness analyzer searches for cases where sub-expressions are always needed by other outer expressions and converts them to eager expressions. 

Its semantics don’t change – that’s why it’s able to do this. And, developers can use the seq primitive to force an expression to evaluate.

Advantages Of Laziness

The lazy execution idea is pretty straightforward. But it comes with great benefits:

  • It makes the program much faster. A Haskell program doesn’t call all functions unless it needs them. This is the opposite in cases like Java or C++, which require a compiler to run the full sorting algorithm, taking much longer than needed. 
  • There is a greater possibility of infinite lists, providing solutions to many list problems. 

Is Haskell a high-level language?

Haskell is a high-level programming language. Keep in mind that the language level is flaky and quite relative. But only assembly languages are low-level languages. All high-level programming languages are abstracted from the native language of the processor.   

Some languages relative to others can be high level or low level. For instance:

  • Ada programming language is a high-level language compared to Assembly language, its medium-level language compared to C, and low-level language compared to Haskell.
  • C is either high or medium-level language compared to Assembly language and low-level language compared to Haskell.

A programming language whose fundamental design allows inherent communication with hardware is considered a low-level language. In this category falls JavaScript, Python, and Haskell, among others. However, Haskell might shift to a medium-level programming language if there is an extremely high-level programming language.  

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Though a high-level language, Haskell can be harsh as a beginner language. So, that calls for understanding the basics right first. Good thing; Haskell is highly flexible in its characteristics, unlike Perl and Python languages. If you select these languages as your first programming language, you probably may not migrate to other programming languages because they have a highly alienated code structure. 

Learning Haskell to the last details takes time due to its broad characteristic base. But that doesn’t make it a so difficult language for beginners. Nonetheless, the effort is much needed. 

High Level vs. Low-Level Languages 

A high-level programming language is designed to make computer programming simpler. Several steps have been removed from the actual code that runs on a computer processor in such programs. As a result, its source code features an easy-to-read syntax, which is later converted into a low-level language. Finally, the CPU recognizes it and runs it. 

There are many low-level languages, and each has a unique syntax. While some are designed for writing desktop software programs, others are tailored for web development. What unites them is the fact that a compiler or an interpreter processes their code before execution. For instance, a code compiled in C++ is compiled to machine code before running. Put simply, these languages require a translator to translate their machine code.

By contrast, lower-level languages sit very close to the set of computer instructions – instructions that the computer understands. Low-level languages are either assembly languages or machine code. 

Machine code: this is an instruction set that the CPU directly understands and can therefore act upon. Any program in machine code has zeros (0) and ones (1) – binary. Writing and debugging them is difficult.  

Assembly language: primarily, they are considered mid-level languages because they are relatively easy to use. However, unlike high-level languages that use statements, assembly languages use mnemonics, i.e., short abbreviations. Each mnemonic corresponds with a machine code instruction—for instance, STA, which stores a value in a memory address. Ideally, a developer writes programs as series of mnemonics as they are much easier to understand and debug than machine code. This gives programmers a more straightforward way of directly controlling a computer.

What is a static type system?

By now, you know that static typic can keep you out of trouble., making it a great option. Nevertheless, dynamic typing lets you work faster, which also makes it excellent. Statically typed and dynamically typed are standard terms in programming languages. the two terms refer to the action of a type checking. – and these two terms refer to different types of systems. 

A type system means a collection of rules, which assign a property to various constructs in a computer program – for instance, expressions, variables, modules, or functions. The purpose here is to remove or reduce the number of bugs by verifying that data is represented correctly throughout a program.

Statically typed languages are programming languages whose variables do not need to be defined before usage. That means that this typing type deals with explicit declaration or initialization of variables before their deployment. 

C, C++, and Java have statically typed languages. However, in C and C++, you can cast variables into other types, but they are not converted – you’ll read them assuming they are a different type. Note that static typing doesn’t mean you need to declare all variables first before using them. Rather. You can initial variables anywhere. However, these require that developers initialize the variable before using them.  

It’s true; static typing avoids bugs in a code, especially in weakly typed languages. It does so by adding more constraints in a compiler; however, it can’t check anything while the program runs in C++ and objective C . these languages allow developers to mix weakly typed C code with a static typed C++ to bypass all other checking types. 

Static Type Checking

When a variable is known at compile time rather than run time, that is a statically typed language, e.g., Haskell. The code compiled can be executed faster since the compiler knows the exact data types; thus, it can produce optimized machine codes using less memory.

Static type checkers only evaluate information that can be determined at compile-time; however, they can verify that the checked conditions hold for all program executions. This eliminates the need for repeating type checks whenever the program is executed. 

Interestingly, a static type checker can easily detect errors in code paths that are rarely used. This is unique because code coverage tests may be unable to find such type errors. The shortcoming of static typing makes it difficult to manually raise a type error in a code because such cod blocks are hardly called. 

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What is meant by is Haskell statically typed?

Are statistically typed languages a relic of the past? Look, these languages allow developers to write down so much information in a program to declare certain variables of certain types. In return, developers get to catch some errors at compile time. The cluttering of the code with noise declarations comes at a high price. These are some reasons that make dynamically typed languages currently more fashionable – their biggest promise is to achieve more within a short time by eliminating static type checking. 

But that doesn’t do away with static languages. Haskell comes in as a strongly typed language with the ability to offer much more. 

Haskell is strongly statistically typed, similar to other functional programming languages. The strong typing gives Haskell the functionality of type inference, a powerful feature at eliminating hidden bugs. All these happens at compile-time, and it minimizes the size of the source code. 

The real benefits of statistically typed languages like Haskell are: 

  • Type inference: the friendly type interface doesn’t need a declaration of the types of your variables. Ideally, the compilers look at how the developer is using them and determine the type they have.
  • Code reuse: in Haskell and other statically typed languages, some generics let developers abstract over type parameters. Specifically, Haskell allows you to write a code piece that can work for several types – the type inference tells you it can work by inferring a non-polymorphic type. 
  • Introducing new datatypes made easy: you can define new types in one line in Haskell. You can give it a new name but has a similar run time as the existing types, but the type system treats it distinctly. 
  • Run type information isn’t by default: after type checking, Haskell erases all type information. The absence of this piece of knowledge implies that a polymorphic code cannot access specific values. This is a robust safety net. Note that Haskell offers developers varying degrees of selective run-time typing. If a developer truly needs it, they can explicitly attach the run-time type information to value and make type-based decisions. 

Typically, in Haskell, functions are simply expressions such as a string or an integer; thus, they have types. Developers can apply functions by rendering arguments. However, it is unnecessary to use all arguments of a function at once – but that varies. Developers can apply an integer function and still have a function that requires a string. 

Dynamic typing

Dynamic typic is a feature programming language that performs type checks at run time instead of statically typed language that performs the checks at compile time. So, a dynamically typed variable is a variable that will not specify the types of the object at the compile time.

  • Dynamically typed languages are sometimes called value typed languages. 
  • A dynamically-typed program uses at least a single dynamically typed variable 
  • A programming language supports dynamic typing if developers can be able to create dynamically typed programs 
  • If most variables in a typical language program are dynamically typed, that makes it a dynamically typed language. 

In this regard, a variable is used in a broader sense, and it may mean things such as class instances or slot slots in structure. 

There a two noting of dynamic typing:

  • Syntactic dynamic typing: in this case, a developer does not need to write type declarations
  • Semantic dynamic typing: this implies that the variable can feature objects of different types

It’s not easy for many developers to get the difference finely, and the type inference further blurs the distinction a little more. 

Keep in mind that type inference is not “syntactic dynamic typing.” That also means it is not dynamic typing and doesn’t type checking.

All dynamically typed languages do not need an explicit declaration of variables before using them. Good examples of such languages include Python and PHP. 

Check out this Python code:

/* Python code */ 

num = 20 // directly using the variable

In this example, a programmer directly assigns a variable num the value 20 before initializing. 

Static Typing and Dynamic Typing vs. Strong Typing and Weak Typing

This represents two different concepts that many people are so much confused about. 

Strong Typing

A strongly typed programming language is one with variables having specific data types. Here, variables are bound to particular data types, like in the case of Java and Python. 

Weak Typing

In this category of programming languages, they aren’t of a specific data type. However, this doesn’t mean that these variables don’t have types. Instead, it indicates that variables are not bound to a particular data type in PHP and C.

All told, Python is both strongly typed and dynamically typed, while Java is strongly typed and statically typed. PHP is dynamic typed and weak typed. On the other hand, C is weakly typed and statically typed. 

The lack of initial variables in dynamically typed languages is a plus to programmers because they can use variables at will without initializing them. 


Luis Gillman
Luis Gillman

Hi, I Am Luis Gillman CA (SA), ACMA
I am a Chartered Accountant (SA) and CIMA (SA) and author of Due Diligence: A strategic and Financial Approach.

The book was published by Lexis Nexis on 2001. In 2010, I wrote the second edition. Much of this website is derived from these two books.

In addition I have published an article entitled the Link Between Due Diligence and Valautions.

Disclaimer: Whilst every effort has been made to ensure that the information published on this website is accurate, the author and owners of this website take no responsibility  for any loss or damage suffered as a result of relience upon the information contained therein.  Furthermore the bulk of the information is derived from information in 2018 and use therefore is at your on risk. In addition you should consult professional advice if required.