Type-checked non-empty strings
A Haskell technique for type-checked non-empty strings using custom data types and compile-time validation, encoding the non-emptiness constraint at the type level to prevent invalid data without runtime checks.
Background
Haskell is a purely functional programming language known for its strong static type system—meaning many bugs can be caught at compile time rather than at runtime. A "type" is a category of data (like String, Integer, or a custom type). A "non-empty string" is a string that is guaranteed by the compiler to contain at least one character, preventing errors from accidentally using blank text. The article explores how to encode this guarantee in Haskell's type system, an example of "type-driven design" or "making illegal states unrepresentable"—a best practice in typed functional programming. Bellroy is an Australian company that occasionally publishes technical essays on software design.