Best practices for writing clean and efficient Haskell code

Are you tired of writing messy code that is difficult to read and maintain? Do you want to improve the performance of your Haskell applications? Look no further! In this article, we will discuss the best practices for writing clean and efficient Haskell code.

Use Strictness

One of the most important aspects of writing efficient Haskell code is to use strictness whenever possible. By default, Haskell is a lazy language, meaning that expressions are only evaluated when they are needed. While this can lead to elegant code, it can also create performance issues when dealing with large data structures or long running computations.

To alleviate these performance issues, you can use the ! operator to force the evaluation of an expression at runtime. This can be particularly useful when dealing with numeric data types, where the overhead of lazy evaluation can be significant.

In addition to the ! operator, Haskell provides a number of ways to control the evaluation of expressions. For example, you can use the seq function to force the evaluation of two expressions in a specific order. This can be useful when dealing with computations that depend on the order of execution.

Avoid Excessive Allocation

Another important aspect of writing clean and efficient Haskell code is to minimize the amount of memory allocation that takes place. Allocating memory can be a costly operation, particularly in functional programming languages where immutability is a common practice.

To avoid excessive memory allocation, you can take advantage of techniques such as data structure reuse, lazy evaluation, and memoization. By reusing data structures rather than creating new ones, you can reduce the overhead of memory allocation.

Lazy evaluation can also be useful in reducing the amount of memory that is allocated. By only computing values when they are needed, you can avoid creating unnecessary data structures.

Memoization is another powerful technique for reducing memory allocation. By caching the results of computations, you can avoid recomputing expensive operations.

Use Appropriate Data Structures

Choosing the right data structure is another key aspect of writing efficient Haskell code. In general, you should choose data structures that provide the appropriate tradeoff between space and time complexity.

For example, when dealing with large sets of data, you might choose to use a hash table rather than a linked list. Hash tables provide constant time lookup and insertion, making them ideal for large collections.

Similarly, when dealing with trees, you might choose to use a balanced binary search tree rather than an unbalanced tree. Balanced trees provide logarithmic time complexity for search, insertion, and deletion, whereas unbalanced trees can have linear time complexity in the worst case.

Use Strict Types

In addition to using strictness, you can also use strict types to ensure efficient memory usage. Strict types are data types that are evaluated immediately, regardless of whether or not they are needed.

One example of a strict data type is the Int type, which is a fixed-width integer type. Because Int values are evaluated immediately, they can be more efficient than other types that are lazily evaluated.

Similarly, when dealing with collections of data, you might choose to use strict collections rather than lazy collections. For example, the Data.Vector module provides strict vector types that can be more efficient than the Data.List module.

Use Profiling Tools

Finally, when writing Haskell code, it is important to use profiling tools to identify performance bottlenecks. Profiling tools allow you to identify which parts of your code are taking the most time and memory.

To get started with profiling, you can use the -prof and -fprof-auto flags when compiling your code. These flags enable profiling and automatically insert cost centers into your code.

Once you have enabled profiling, you can use tools such as hp2ps and hp2anything to generate visual reports of your program's performance. These reports can show you which functions are taking the most time and memory, allowing you to focus your optimization efforts.


In conclusion, writing clean and efficient Haskell code is an important skill for any Haskell developer. By using strictness, avoiding excessive allocation, using appropriate data structures, using strict types, and using profiling tools, you can ensure that your programs are both elegant and efficient.

So what are you waiting for? Start implementing these best practices in your Haskell code today and watch your performance soar!

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