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Type-checked non-empty strings
9 days ago
- The article describes a Haskell technique for creating type-checked non-empty strings using RequiredTypeArguments from GHC 9.10.
- It presents a type-level validation mechanism that replaces TemplateHaskell calls, leading to a ~10% build-time improvement in a data-heavy package.
- The technique uses a type family or typeclass to enforce non-empty strings at compile time, with custom error messages for invalid inputs.
- Examples include implementing a NonEmptyText type and extending the approach to validate DynamoDB table names with regex-like constraints.
- The article notes limitations, such as GHC's reduction limit and complexity in expressing non-trivial algorithms at the type level.
- It concludes by discussing the trend towards Dependent Haskell and acknowledges potential risks with UndecidableInstances.
Data-Directed Programming in Haskell
3 days ago
- The article discusses implementing data-directed programming in Haskell as seen in SICP 2.4.3, starting with tagged data and moving to an explicit operation table.
- It shows how to handle complex numbers in rectangular and polar forms using generic functions, and transitions to Haskell type classes for a cleaner, type-safe approach.
- The implementation allows for generic return types and uses existential types (AnyComplex) to create homogeneous collections of different representations.
- Type classes are compared to explicit dictionaries, highlighting compile-time safety and conciseness over Lisp's dynamic approach.
Low-level Haskell: The cursed way to emulate inline assembly in Haskell/GHC, or
3 days ago
- Haskell (GHC) lacks inline assembly or intrinsics like C/C++, but techniques exist to use CPU-specific instructions.
- Multiple methods to return 128-bit products from 64-bit multiplication include C FFI with pointers, unsafe/safe FFI, foreign import prim, and using SIMD registers.
- Foreign import prim allows low-overhead custom primops via assembly thunks, closely matching performance of GHC's built-in timesWord2# intrinsic.
- Benchmarks show timesWord2# is fastest (~4.0ns), followed by foreign import prim (~4.5ns); unsafe FFI with double calls is competitive (~5.8ns), while safe FFI is slowest (>60ns).
- Using unsafe FFI over safe FFI is crucial for performance in short, non-blocking foreign calls to avoid GC blocking and overhead.

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Type-checked non-empty strings

Data-Directed Programming in Haskell

Low-level Haskell: The cursed way to emulate inline assembly in Haskell/GHC, or