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+Style: before writing or reviewing `.hon` code, read [docs/style.md](docs/style.md).
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 Honey is currently bootstrapped with the Bro compiler. The expected development workspace places the Bro project at [`../brolang`](../brolang); consult that project for compiler behavior and documentation.
 
+Style: see the [language guidelines](docs/style.md).
+
 Build Honey from this directory:
 
 ```sh
diff --git a/docs/style.md b/docs/style.md
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+# Honey style
+
+These guidelines apply to Honey programs, the compiler, and the standard library. The compiler is currently written in Bro; apply the same conventions using syntax supported by the bootstrap compiler.
+
+## Names
+
+- Use `snake_case` for procedures, variables, fields, and enum members; `PascalCase` for types; `SCREAMING_SNAKE_CASE` for named sentinel constants.
+- Choose names that describe the value or operation. Short loop indices are appropriate when their meaning is local.
+- Qualify imported operations with their module, such as `mem.alloc` and `ast.node_count`. Mark file-local implementation details with `@hide:file`.
+
+## Bindings and types
+
+- Prefer `::` for bindings that stay fixed; use `:=` for bindings that change.
+- Infer types when the initializer makes the intended type clear. Write an explicit type when it determines representation, mutability, or a public contract.
+- Request mutable pointers and slices only when the operation needs to modify their contents.
+- Give aggregates meaningful defaults. Use `undefined` only when every value that can be read is assigned first.
+
+## Layout and control flow
+
+- Use four-space indentation and put opening braces on the declaration or control-flow line.
+- Use single-line bodies for simple operations. Use braces for multiple statements or nested control flow.
+- Break long parameter lists and aggregate initializers across lines, with a trailing comma on the last item.
+- Use early returns for terminal cases so the main path stays shallow.
+- Register `defer` cleanup immediately after acquiring a resource. Use `errdefer` for cleanup needed only until ownership is transferred successfully.
+- Write comments for invariants, ownership, or reasons that the code alone does not explain. Use `#!` for API documentation.
+
+## Library operations
+
+- Reuse an existing standard-library operation when it expresses the work directly.
+- Use `mem.set(destination, value)` when assigning the same complete typed value to every element of a mutable slice. This preserves the value's fields; it is not a byte-wise zeroing operation.
+- Keep a loop when only one field is initialized, values differ by element, or initialization shares a pass with other work. A helper should not introduce unnecessary writes or another traversal.
+
+When editing or reviewing code, apply every relevant guideline to the changed code. Keep unrelated formatting changes separate.