WebAssembly and MoonBit

Bottom line

MoonBit is the clearer choice when WebAssembly is the primary goal. Nim offers broader native and C/C++ integration: its usual WASM route is Nim → C/C++ → Emscripten → WASM, while MoonBit directly targets wasm and wasm-gc.

Concern	Nim	MoonBit
WASM role	Distribution target through C/C++ tooling	First-class target
C/C++ integration	Very strong	Native/C support; WASM is host-FFI oriented
Native use	Strong	Supported, but not the primary focus
AST macros	Very strong	Not as macro-centric

Nim's generated C, runtime, memory management, Emscripten runtime, and JS glue can affect size and startup. MoonBit's wasm-gc can use GC reference types, but FFI boundaries still require deliberate design.

For a SQL parser, retain Nim when native/Rust C ABI integration, macros, C/C++ libraries, and code reuse matter. Evaluate MoonBit when browser WASM, small binaries, startup time, JS string exchange, and WASM GC dominate. Measure the existing Nim WASM version before porting: size, startup, parse throughput, transfer time, peak memory, AST-return cost, and diagnostics.