Lexing, Parsing, and Compiler Frontends in the Real World: Pratt Parsing, LR/GLR, Error-Tolerant Trees for IDEs (Tree-sitter, Roslyn), and Bidirectional Type Checking

Deep End Era. Engineering with Sankalp · Oct 29, 2026 · 1h 7m

In a batch compiler, a single missing semicolon can abort the build; in an IDE Language Server, the code is missing semicolons and closing braces on almost every keystroke, yet autocomplete must respond in ten milliseconds. We unpack how real-world compiler frontends work: SIMD lexing, Vaughan Pratt's 1973 operator-precedence algorithm, LR vs Tomita GLR in Tree-sitter, Roslyn's Red-Green immutable syntax trees, and Bidirectional Type Checking.

Chapters

00:00:00 Opening: Why Your Compiler Textbook Lied to You About How Modern Compilers Work

00:03:43 Lexical Analysis: Maximal Munch, SIMD…