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Parsing JSON Objects without intermediate ASTs

The author presents an alternative approach to JSON parsing that avoids constructing an intermediate abstract syntax tree (AST), instead using partially-initialized data structures directly to reduce allocation and computational overhead. While demonstrated in Haskell, the technique is also applicable to languages with ADTs and staged metaprogramming like Rust.

Background

JSON parsing is ubiquitous in modern software, but most libraries build a full AST before extracting application-specific data, incurring unnecessary memory and CPU costs. This post explores a zero-allocation parsing strategy aimed at performance-sensitive applications.

Source
Lobsters
Published
Sep 23, 2026 at 12:28 PM
Score
6.0 / 10