Extreme Haskell: Typed Expression EDSLs (Part 1)

A deep dive into building a fully type-safe embedded domain-specific language (EDSL) in Haskell that represents a typed lambda calculus. Starting from an untyped expression ADT, the post progressively adds phantom type indices, singletons, existentials, runtime type equality, typed records and sums using vinyl-style heterogeneous lists, and finally a scoped variable environment that makes ill-typed or unbound variable references impossible to construct in Haskell. The result is an expression language where GHC statically rejects any invalid domain-level term. The series aims to eventually compile these typed expressions to multiple backends (C, JavaScript) and generate Graphviz visualizations of state machines.

Nguồn: https://blog.jle.im/entry/extreme-haskell-typed-expression-edsls-1.html. 8sync News chỉ tóm tắt và dẫn link; bản quyền nội dung thuộc tác giả và nguồn gốc.

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Haskell for all: Mechanized type inference for record concatenation

A deep technical exploration of type inference for biased record concatenation (the // operator in Nix), formalizing the 1991 Wand paper algorithm that no language has fully implemented. The post presents three formalizations: declarative natural deduction semantics, an algorithmic constraint generation and resolution approach, and a ~400-line reference Haskell implementation. Key concepts covered include row-polymorphic record types, field annotations (present/absent/unknown), a canonical field concatenation operator with monoid laws, sibling row variables, disjoint set data structures for tracking variable relationships, and field instantiation for handling record unification mismatches. A companion GitHub REPL is provided for testing.

#general-programming