# Guile Style Guide for Safsaf

This guide draws on
[Riastradh's Lisp Style Rules](https://mumble.net/~campbell/scheme/style.txt),
the [Guix Coding Style](https://guix.gnu.org/manual/1.5.0/en/html_node/Coding-Style.html).

---

## Formatting

### Indentation

Use **2-space indentation**, no tabs. When a subform follows the
operator on the same line, align subsequent subforms to that column.
When the first subform is on the next line, align it with the operator.
Special forms (`define`, `let`, `lambda`, `if`, `cond`, `match`, etc.)
follow standard Scheme indentation.

### Line Length

Do not exceed **80 columns**.

### Parentheses

Never place closing parentheses on their own line. Do not put spaces
after opening parentheses or before closing ones.

### Blank Lines

Separate top-level forms with a single blank line. Do not place blank
lines in procedure bodies except to separate internal definitions from
the body.

### Square Brackets

Do not use square brackets. They are non-standard and non-portable.


## Naming

Write names with **English words separated by hyphens**. No underscores,
camelCase, or abbreviations.

- **`?` (predicates):** Boolean-returning questions. E.g., `route?`,
  `logged-in?`.
- **`!` (mutation):** Procedures whose primary purpose is destructive
  update. E.g., `set-route-handler!`. Do not append to every procedure
  with side effects.
- **`%` (private):** Module-private bindings. E.g., `%make-route`,
  `%email-rx`.
- **`*` (variants):** Variations on a theme (`let*`, `define*`).

### Records

```scheme
(define-record-type <route>
  (%make-route method pattern handler name)   ; internal constructor
  route?                                       ; predicate
  (method  route-method)                       ; accessor
  (handler route-handler set-route-handler!))  ; accessor + setter
```

- `make-foo` for public constructors, `%make-foo` for raw constructors.
- `foo?` for predicates, `foo-field` for accessors, `set-foo-field!`
  for setters.

### Parameters and Dynamic State

- Guile parameters use the **`current-`** prefix: `current-session`,
  `current-csrf-token`.
- **`with-`** establishes dynamic state and calls a thunk.
- **`call-with-`** calls a procedure with arguments, managing resources
  or continuations.

### Local Variables

Use meaningful names. Single-letter names only for unambiguous index
variables in tight loops.


## Comments

```scheme
;;;; file-heading.scm — File Heading

;;;
;;; Section Heading
;;;

;;; Top-level explanatory comment.

(define (fnord zarquon)
  ;; Fragment comment before code.
  (quux zot mumble             ;margin note
        frotz))
```

- **`;;;;`** — File headings.
- **`;;;`** — Section headings (use the sandwich: `;;;` / `;;; Title` /
  `;;;`) and top-level explanations.
- **`;;`** — Fragment comments, before the code they describe.
- **`;`** — Margin comments, after code on the same line.

Write comments only where the code cannot explain itself.


## Docstrings

All public procedures must carry a docstring. Place it as the first
expression after the parameter list. Describe what the procedure does,
its parameters, and return values:

```scheme
(define* (route method pattern handler #:key (name #f))
  "Create a route.  METHOD is a symbol, list of symbols, or '* for any.
HANDLER is a procedure (request body-port) -> (values response body).
NAME is an optional symbol used for reverse routing with path-for."
  ...)
```

For parameters, use `set-procedure-property!` with `'documentation`.


## Module Definitions

Use `define-module` with `#:use-module` and `#:export`. Group imports:

1. **Standard library** — `(ice-9 ...)`, `(web ...)`
2. **SRFIs** — `(srfi srfi-1)`, `(srfi srfi-9)`, etc.
3. **External dependencies** — `(knots ...)`, `(webutils ...)`, `(json ...)`
4. **Internal modules** — `(safsaf ...)`

Prefer `#:use-module`; use `#:autoload` for heavy or circular deps.
Standalone scripts may use `use-modules` instead of `define-module`.


## Procedures

- No more than **four positional parameters**. Use keyword arguments
  (via `define*`) beyond that.
- Keep procedures under roughly **21 lines** (excluding docstring).
  Break long procedures into meaningfully named helpers.
- Prefer **purely functional** code. Use mutation only for I/O,
  performance, and low-level utilities.
- Avoid point-free style and functional combinators. Use explicit
  `lambda`. Reserve `compose` for cases where composition is genuinely
  the idea being expressed.


## Data Types

- Prefer **records** (`define-record-type` from `(srfi srfi-9)`) over
  ad-hoc lists. Do not browse data with `car`/`cdr`/`cadr`.
- Do not export record type descriptors (e.g., `<route>`). Export only
  predicates, constructors, and accessors.
- Use `(ice-9 match)` for pattern matching.
- Use **alists** for lightweight key-value data (route params, headers,
  config).


## Multiple Return Values

Use `values` for multiple return values. Prefer `(srfi srfi-71)` extended
`let` over `(srfi srfi-11)` `let-values`:

```scheme
(let ((response body (handler request body-port)))
  (values response body))
```


## Error Handling

Use `(ice-9 exceptions)` functionality.


## File Organization

- Keep files under **512 lines**. Do not exceed 1024.
- Minimize module dependencies.
- Structure files with `;;;` section headings.


## Testing

Tests use `define-suite`, `suite`, `test`, and `is`. Keep test files
under `tests/`.