In earlier articles, we have implemented a tokenizer, parser, and transformer to convert WAT syntax to a Wasm AST, and got started on the code generation.

In this part, we’ll finally wrap up code generation and be able to compile our hello world sample into something that wasmtime can run.

I hope.

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In earlier articles, we have implemented a tokenizer, parser, and transformer to convert WAT syntax to a Wasm AST and got started on the code generation. This part will continue with code generation. We’ll start with the import section because it has a couple interesting complications that we need to take into account. The Import Section Consider this wat import statement: (module (import "wasi_snapshot_preview1" "fd_write" ( func $fd_write (param i32 i32 i32 i32) (result i32)) ) ) If we look at the bytes in the binary representation of this section, it’s surprisingly long:

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In earlier articles, we have implemented a tokenizer, parser, and transformer to convert the Web Assembly Text Format to an Abstract Syntax Tree that can hopefully easily compile to Wasm. Truthfully, the next step should be validation. Validation is the process of statically analyzing the syntax tree to catch as many errors as possible. This is where things like type checking and borrow checking happen, for example. The wasm spec has an in-depth description of what validation should look like for a conforming compiler.

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In earlier articles, we implemented a tokenizer and parser to convert Wasm’s WAT syntax into an S-expression abstract syntax tree and started to implement a transformer to convert that AST into one more suitable for generating Wasm bytecode. Now that the boilerplate is in place, this article will continue to implement recursive transformer functions, getting into some of the more complicated expressions in the “hello world” WAT example. I should mention that the code in this article gets long and repetitive.

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