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Haskell vs. PureScript: The difference is complexity

Haskell and PureScript each provide their own unique development advantages, so how should developers choose between these two popular programming languages?

Reliance on immutable data structures is a key aspect of functional programming. By defining variables at the outset, programming languages like Haskell and PureScript aim to help developers write bug-free code, particularly in production systems and research.

This article examines key feature similarities and differences between PureScript and Haskell to help developers discern the types of projects each language is best suited for.

Haskell: A practical approach to complex programming

Haskell is an open source programming language that contains a broad selection of packages made available through public package servers. Haskell has a static typing system, features a concise syntax and is competent at detecting errors at compile time.

One particularly attractive aspect of Haskell is its embrace of programming concepts like immutability, lazy evaluations and strict types. Haskell also places an emphasis on monads and monad transformers, which developers can use to describe computations as a sequence of steps.

Another unique feature of Haskell is that it is also a "lazy" language. Using a technique called lazy evaluation, Haskell-based programs wait as long as they possibly can to call the functions and extract the values necessary to evaluate an expression. This means that Haskell typically won't execute operations or calculate types until required to show a result, offering programmers the option to write control structures like if-then-else.

Developers can give their programs explicit directions to take certain actions by applying and composing pure functions along with immutable data -- in Haskell, data structures are immutable by default. Haskell also simplifies the creation of clean and simple abstractions, while enabling developers to render declarative code.

Haskell's strict type system may require a little more development expertise to work with, but it's highly expressive and incorporates a lightweight, elegant syntax to describe functions. If the codebase compiles, programmers can be relatively assured the software will run without errors. Glasgow Haskell Compiler also offers developers that use the language access to a high-performance parallel garbage collector and lightweight concurrency library stocked with readily accessible primitives and abstractions.

However, programming operations in Haskell often relies on sophisticated levels of functional thinking and mathematics, which could present a steep learning curve for newer programmers or those not experienced in complex computational programming. The language exposes many underlying details that would otherwise remain hidden from most developers as abstracted library implementation code.

PureScript: Lean code for functional, front-end applications

While conceptually similar to Haskell, PureScript offers straightforward installation and build processes, helping developers create either simple or complex front-facing applications that are easy to refactor, debug and test. PureScript is strongly typed and purely functional. Also, it compiles to JavaScript and offers type classes that enable programmers to create reusable code.

PureScript tends to find more favor among developers looking to learn functional paradigm concepts within the safety of easier installation and build processes. The high granularity of PureScript's type classes also eliminates the need for many of the language extensions JavaScript developers typically rely on, such as TypeScript, Flow and JSDoc.

PureScript Registry on GitHub acts as a repository for packages and metadata, where developers can also find access to APIs that handle tasks like registering, updating, transferring and unpublishing packages. While libraries for PureScript are stable and secure, the language is best suited for front end-facing work, particularly single-page web applications. Unfortunately, the language doesn't yet enjoy the mature ecosystem of libraries it would need to fully support more intensive back-end development efforts.

PureScript's dedicated syntax for creating, updating and accessing records arguably offers it an advantage over languages like Haskell. Since PureScript bases all records on row polymorphism, programmers can write unique collections of functions for record access and retrieval. The PureScript compiler infers most types and works to prevent programmers from releasing bug-filled code into production environments. Instead, the language obligates developers to resolve errors at the outset, pushing off extra work until later.

PureScript also uses a rich type system to downplay some of the complexities associated with functional programming, such as overly verbose code or a lack of abstraction capabilities. Due to its ability to quickly generate human-readable code, PureScript offers a useful balance between the theoretical advantages of functional programming and the practical speed of JavaScript. The language's expressive types and support for type inference also reduce the number of type annotations developers have to create compared to what is required in languages like Haskell.

Pursuit, a coding boot camp website, hosts PureScript API documentation. Programmers can search capabilities for hundreds of PureScript libraries to build everything from simple applications to web services and games. Developers can express many common patterns, whether they are mapping over and traversing the properties of a record or merging and zipping using type-safe actions. However, keep in mind that porting libraries from Haskell to PureScript can potentially introduce mismatched types and other performance-hampering issues related to data or variables.

In the end, Haskell's strong focus on type influences how programmers continue to write sophisticated, complex code once they learn its main properties. For PureScript developers, reusable code and a straightforward approach to records and polymorphism offer some compelling advantages for primarily front-end development.

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