Haskell is a powerfully expressive language, often used for solving complex problems in an elegant and concise manner. This characteristic of Haskell also makes it suitable for solving common problems that are similar in nature, such as checking if a list is empty. This might seem like a straightforward problem, but it’s a common task that developers perform across different programming languages.
This article will dig into this common problem and demonstrate how to tackle it using Haskell. We will write and explain a function that returns “False” if a list is empty and “True” if it otherwise.
isEmpty :: [a] -> Bool isEmpty  = True isEmpty _ = False
This Haskell function works in a straightforward manner. The function `isEmpty` takes a list of any type (denoted by [a]) and returns a Boolean. If the list is empty (), it returns True, else it will return False. This function highlights the power of Haskell’s pattern matching.
Haskell has a rich set of libraries that you can use to solve problems in a more efficient manner. Some libraries that directly or indirectly relate to our problem of checking if a list is empty include:
- Data.List: A core Haskell library that provides functions for list manipulations. It doesn’t include the ‘isEmpty’ function as implemented above, but it provides many functions related to list manipulation including checking if a list contains a specific element.
- Safe: This library offers some additional safety to Haskell by providing versions of functions that don’t fail unexpectedly.
Using libraries can make your code more efficient and easier to understand, so it is always good practice to be aware of the libraries available and how they can help.
The function that we have discussed to check if a list is empty employs a powerful Haskell feature known as pattern matching. Pattern matching in a function definition allows you to create different outputs depending on the input structure.
For example, in our “`isEmpty“` function, we define two “patterns” to match. If the input matches the pattern of an empty list (), our function outputs True. For any other pattern represented by the underscore (_), it outputs False. Pattern Matching is fundamental in many Haskell functions and is quite an elegant aspect of the language, enabling us to write cleaner and more readable code.
In conclusion, the discussed Haskell function and libraries, along with the concept of pattern matching, allow for great efficiency and elegance when dealing with the problem of checking if a list is empty.