Haskell is a statically typed, purely functional programming language with type inference and lazy evaluation. It is designed for teaching, research, and industrial applications.
Haskell Anti-Patterns Overview
Haskell, despite being a powerful and elegant functional language, has several common anti-patterns that can lead to performance issues, maintainability problems, and bugs. Here are the most important anti-patterns to avoid when writing Haskell code.
String Concatenation with ++
Avoid using ++
for repeated string concatenation, as it has O(n²) complexity. Use more efficient data structures like Text
or ByteString
, or techniques like ShowS
or Builder
.
Partial Functions
Avoid partial functions like head
, tail
, fromJust
, etc. that can crash on certain inputs. Instead, use pattern matching or return Maybe
or Either
to handle all possible cases.
Inefficient List Processing
Avoid creating intermediate lists when processing data. Use higher-order functions like foldr
, foldl'
, or foldMap
for more efficient processing.
Not Using Strictness Annotations
Use strictness annotations (!
) for data fields that should be evaluated eagerly, especially in numeric computations, to avoid space leaks and improve performance.
Using String Instead of Text or ByteString
Avoid using String
(which is a linked list of characters) for text processing. Use Text
or ByteString
for better performance with large text data.
Not Using Newtypes
Use newtype
instead of type
for type aliases to get compile-time type checking and avoid mixing up values of the same underlying type but different semantic meanings.
Excessive Use of Point-Free Style
Avoid excessive point-free style that makes code hard to read. Use named parameters and intermediate values when it improves clarity.
Not Using Record Syntax
Use record syntax for data types with multiple fields to get accessor functions for free and make field access more explicit and maintainable.
Not Using Language Extensions Appropriately
Use appropriate language extensions like DeriveFunctor
, RecordWildCards
, or OverloadedStrings
to make your code more concise and expressive.
Not Using Smart Constructors
Use smart constructors to ensure that invalid states cannot be represented. Hide data constructors and expose only functions that create valid values.
Using IO Unnecessarily
Keep functions pure (without IO) whenever possible. Only use the IO monad when you actually need to perform input/output operations.
Not Using Appropriate Monads
Use appropriate monads and monad transformers for different concerns like error handling (Either
, ExceptT
), configuration (Reader
), or state (State
).
Not Using Lenses for Deep Updates
Use lenses (e.g., from the lens
package) for working with nested data structures, especially when you need to update deeply nested fields.
Not Using Type Classes Appropriately
Use type classes to define common interfaces for different types, enabling polymorphic functions and reducing code duplication.
Not Using Proper Error Messages
Provide descriptive error messages and use structured error types. Avoid using error
or undefined
in production code.
Using Lazy I/O
Avoid lazy I/O which can lead to resource leaks and unpredictable performance. Use strict I/O or streaming libraries instead.
Not Using Proper Project Structure
Organize your code into modules with clear responsibilities. Follow a consistent project structure to make your codebase more maintainable.
Not Using Proper Dependency Management
Use proper dependency management tools like Cabal or Stack to manage your project’s dependencies and build process.
Not Using Proper Testing
Write proper tests using frameworks like HUnit, Hspec, or QuickCheck. Use property-based testing when appropriate.
Not Using Proper Documentation
Document your code with Haddock comments. Include descriptions, examples, and edge cases to help users understand how to use your functions.