Where Clause Haskell

Other Programming Languages

In Haskell, the “where” clause is a powerful feature that allows you to define local bindings for variables within a function. It provides a clean and concise way to declare intermediate values or helper functions that are only relevant to a specific block of code.

Personally, I find the “where” clause to be one of the most elegant and efficient ways to enhance the readability and maintainability of my Haskell code. It enables me to break down complex computations into smaller, more manageable pieces, making my code easier to understand and debug.

Let’s dive deep into the details of how the “where” clause works in Haskell.

Defining a “where” clause

The “where” clause is typically used in function definitions. It follows the main function body and consists of one or more bindings enclosed within curly braces.

Here’s an example to illustrate its usage:

sumSquare :: Int -> Int -> Int
sumSquare x y = squareSum
squareSum = (x * x) + (y * y)

In this example, we have a function called “sumSquare” that takes two integer arguments, “x” and “y”. Instead of directly performing the computation within the function body, we use a “where” clause to define the intermediate value “squareSum”. This intermediate value is then used to calculate the final result.

Benefits of using a “where” clause

The “where” clause provides several benefits:

  • Code organization: By defining local bindings within a “where” clause, you can logically group related code together. This makes your code easier to read and follow.
  • Reusability: The variables defined in a “where” clause can be used multiple times within the function body. This allows you to avoid duplication and improve code reuse.
  • Readability: By giving well-named intermediate values a clear purpose, you can enhance the readability of your code. Meaningful names make it easier for others (and your future self) to understand the intention behind the code.

Scoping rules

The variables defined within a “where” clause are only visible within the function where the “where” clause is defined. They are not visible outside the function, ensuring that the code remains encapsulated and modular.

It’s important to note that the variables defined in the “where” clause cannot be accessed from other functions or code blocks within the same function.


The “where” clause in Haskell is a powerful tool that enhances code readability, maintainability, and organization. It allows you to define local bindings within a function and encourages breaking down complex computations into smaller, more manageable pieces.

Personally, I highly recommend utilizing the “where” clause whenever you need to introduce intermediate values or helper functions within your Haskell code. It will not only make your code cleaner and more readable but also enhance your overall programming experience.