Compiler Architecture

Ferricel compiles CEL expressions into self-contained WebAssembly modules. The process involves two distinct Rust artifacts: the runtime and the compiler.

The Runtime

The runtime crate is a Rust library compiled to wasm32-unknown-unknown. It provides the low-level functions that a compiled CEL program calls at execution time, like memory allocation, value serialization, arithmetic helpers, string operations, and so on. Because the target is bare Wasm (no WASI, no OS), it is entirely self-contained.

The Compiler

ferricel-core contains the compiler. It parses the CEL source using the parser that is part of the cel crate. The parser produces a typed AST, which the compiler then traverses, emitting WebAssembly instructions. The WebAssembly instructions are produced using the walrus crate.

Rather than generating a Wasm module from scratch, the compiler loads the pre-embedded runtime.wasm module and injects the compiled CEL program into it. A dead-code-elimination pass (based on walrus::passes::gc) then removes any runtime functions the program does not call, keeping output files small.

The result is a single .wasm file that is fully self-contained and can be executed anywhere a WebAssembly runtime is available.