# MACH
C23 web framework. App = `config mach()` returning `(config){...}` of resources, databases, modules, etc. Each request runs a pipeline of steps over a shared per-request context. Memory, threads, and I/O are managed by the framework. Tasks and events are durable.
---
## CRITICAL RULES — read these BEFORE writing any code
Almost every bug a small model writes in MACH comes from breaking one of these.
Skim once, refer back often.
### Rule 1 — NEVER use dot notation in `{{ }}`
The character `.` is **forbidden** between `{{` and `}}` anywhere in any
template, SQL string, URL, or interpolated string. The MACH interpreter
treats `{{a.b}}` as an unknown key and renders it as the **empty string**.
You access nested data **only** by entering nested sections with
`{{#name}}...{{/name}}`. The shape of the template must mirror the shape
of the context.
> **Self-check before emitting any tag**: is there a `.` between `{{` and `}}`?
> If yes, the template is wrong. Stop, rewrite with sections.
#### Pattern A — Single root scalar (from `.context`)
A scalar seeded into root context is read directly. There is nothing to
"dot through" in this case; this pattern just shows the baseline.
```c
.context = {{"site_name", "MACH App"}}
```
```html
✅
{{site_name}}
```
#### Pattern B — One-row flat access (single-row `find()` / `query()` result)
Even a single-row result is stored as a **table**. Fields are not at
root scope. Open the section, then read the field.
```c
find({.set_key = "todo", .db = "todos_db",
.query = "select id, title from todos where id = {{id}};"})
```
Context after the step:
```
{ todo: [ { id: 5, title: "Learn MACH" } ] }
```
```html
✅ {{#todo}}
{{title}}
id={{id}}
{{/todo}}
❌ {{todo.title}} renders ""
❌
{{title}}
renders "" (not inside #todo)
❌ {{#todo}}{{todo.title}}{{/todo}} renders "" (dot still banned)
```
#### Pattern C — After `join()`: parent + nested children
The most common nested-context scenario in MACH. Concurrent `query()`
produces two **sibling** tables; `join()` then **moves** the children
inside each parent record. After the join, the children are no longer
accessible at root — the template MUST enter the parent section to
reach them.
```c
query(
{.set_key = "project", .db = "projects_db",
.query = "select id, name from projects where id = {{id}};"},
{.set_key = "tasks", .db = "projects_db",
.query = "select id, project_id, title from tasks where project_id = {{id}};"}
),
join(
.target_table_key = "project",
.target_field_key = "id",
.nested_table_key = "tasks",
.nested_field_key = "project_id",
.target_join_field_key = "tasks"
),
```
Context shape, before vs after the join:
```
after query(): { project: [{id, name}],
tasks: [{id, project_id, title}, ...] } // siblings
after join(): { project: [{id, name,
tasks: [{id, project_id, title}, ...]}] } // tasks now INSIDE project
```
```html
✅
{{#project}}
{{/project.tasks}} dot in section name
❌ {{#tasks}}
{{title}}
{{/tasks}} renders nothing — after join(),
tasks lives INSIDE project,
not at root. No dot, but
still wrong: must open
{{#project}} first.
❌
{{name}}
renders nothing — name is a
field of the project record,
{{#tasks}}
{{title}}
{{/tasks}} not a root key. Even though
{{#tasks}} is correctly
wrapped, {{name}} at root
reads from root scope where
no "name" key exists.
EVERY field of the parent —
its scalars AND its nested
children — requires opening
{{#project}} first.
```
The last two counter-examples are the subtle ones — there are no
dots, but the templates still render empty. Both fail because the
template doesn't enter the parent section. **After a `query()` that
sets `project`, every field of the project (its own `name` and `id`,
AND any tasks joined into it later) lives inside the project record,
not at root.** Wrapping only the children in `{{#tasks}}` while
leaving `{{name}}` and `{{id}}` at root is a half-fix that produces
silent empty output.
Rule of thumb: **if you are reading any field that came from a
`query().set_key = "project"`, you must be inside `{{#project}}`.**
That includes the project's own scalars. There is no "partial entry"
into a record — you're either inside the section or you're at root.
The last counter-example is the subtle one: a join doesn't *copy* the
children, it **moves** them. Iterating `{{#tasks}}` at root after the
join silently produces nothing, even though there's no dot.
#### Pattern D — 3+ levels of nested sections
After multiple `join()` steps, or from nested JSON returned by `fetch()`,
context can be arbitrarily deep. Walk down level by level with one
section per level.
Context shape:
```
{ org: [ { name: "Acme",
projects: [ { title: "Site",
tasks: [ { label: "Design" }, { label: "Build" } ] } ] } ] }
```
```html
✅
{{#org}}
{{name}}
{{#projects}}
{{title}}
{{#tasks}}
{{label}}
{{/tasks}}
{{/projects}}
{{/org}}
❌ {{org.name}} renders ""
❌ {{org.projects.title}} renders ""
❌ {{org.projects.tasks.label}} renders ""
❌ {{#org}}{{projects.title}}{{/org}} renders ""
❌ {{#org.projects}}{{title}}{{/org.projects}} dot banned in section names too
❌ {{#org}}{{#projects}}{{tasks.label}}{{/projects}}{{/org}} still has a dot
```
#### Pattern E — Iterating an array of nested sections
A `{{#name}}...{{/name}}` block automatically loops when `name` is an array.
Every iteration enters one record. Nested arrays loop the same way inside.
Context shape:
```
{ projects: [
{ title: "A", tasks: [{ label: "x" }, { label: "y" }] },
{ title: "B", tasks: [{ label: "z" }] }
] }
```
```html
✅
{{#projects}}
{{title}}
{{#tasks}}
{{label}}
{{/tasks}}
{{/projects}}
❌ {{#projects}}{{tasks.label}}{{/projects}} dot banned
❌ {{projects.title}} dot banned
❌ {{#projects.tasks}}...{{/projects.tasks}} dot banned
```
**Recap.** All five cases — flat single-row access, post-`join()`
parent/children, 3+ level nesting, iteration of nested arrays — use
the **same one rule**: open a section for every level, then read fields
by their bare name. There is never a reason to type a `.` inside
`{{ }}`. If you find yourself writing one, the data shape is fine; the
template is wrong. Add a section.
And remember the silent failure mode from Pattern C: after a `join()`,
the joined-in table is no longer at root. `{{#tasks}}` at root after
joining tasks into project renders nothing — open `{{#project}}` first.
> **Helpers like `{{url:name}}`, `{{input:title}}`, `{{error:title}}`,
> `{{precision:total:2}}` use `:` (colon), not `.` (dot)** — those are
> not dot notation and are fully supported.
#### Template Checklist — run this BEFORE typing any `render(.template = ...)` or template asset
A small model gets here, holds Rule 1 in mind for half a second, then
slips back into training-set Mustache habits ("`{{thing.field}}`"). The
checklist exists to catch that slip the moment it happens.
For **every** `{{ ... }}` you are about to type, walk these three checks:
**Check 1 — Is there a `.` between `{{` and `}}`?**
- YES → **STOP. The template is wrong. Do not emit the tag.** Add a
section instead and read the bare field inside.
- NO → continue to Check 2.
**Check 2 — Is the bare name reachable from the *current* nesting level?**
- At root scope, only top-level context keys are reachable.
- Inside `{{#project}}...{{/project}}`, only fields of the current
`project` record are reachable.
- After `join(... → project)`, the joined-in table (`tasks`, `comments`,
whatever) **moved** — it is no longer at root, only inside `project`
records.
- If the field is not at the current level, you need to open one or
more sections to enter the right scope. Go to Check 3.
**Check 3 — How many levels deep is the field?**
- Count the levels: root → table → record-field is 1 section deep
(`{{#table}}{{field}}{{/table}}`).
- A nested table inside a record (e.g. `tasks` inside `project` after
a join) is 2 sections deep
(`{{#project}}{{#tasks}}{{title}}{{/tasks}}{{/project}}`).
- Three nested levels = three section wrappers. Always exactly the
same number of `{{#...}}{{/...}}` pairs as levels of nesting.
If any check fails, do not emit the tag — fix it first.
> **The rule has zero exceptions.** Not in `render(.template = ...)`,
> not in templates loaded from `.context`, not in SQL `{{interpolation}}`,
> not anywhere a `{{` appears in MACH source. If you find yourself about
> to type `.` between `{{` and `}}`, the template is wrong.
---
### Rule 2 — ONE database per DOMAIN, not one database per table
A database holds many tables. Group every table that belongs to the same
business domain into one database. **Do not** create one database per
table — that is the most common mistake a small model makes here.
#### What "domain" actually means in MACH
> **A "domain" is what one MODULE owns — a feature slice of the app,
> not a noun in your data model.** A `projects` module owns
> *everything* about projects: project records, the tasks attached to
> them, comments on those tasks, project tags, daily project counts,
> archived projects. All of that lives in **one** database
> (`projects_db`) with **many** migrations (one per table).
>
> Tasks are NOT their own domain just because "tasks" is a noun.
> Tasks are part of the projects domain because tasks belong to
> projects.
>
> A new domain (= a new database) appears only when a new **module**
> appears — adding a `billing` module gives you a `billing_db`. Adding
> a new table inside the existing `projects` module does **not** give
> you a new database; it gives you a new migration in `projects_db`.
#### ✅ Correct: one database per domain, many tables inside
A `projects` domain owning `projects`, `tasks`, `comments`, `tags`:
```c
.databases = {{
.engine = sqlite_db,
.name = "projects_db", // one db for the whole domain
.connect = "file:projects.db?mode=rwc",
.migrations = {
"CREATE TABLE projects ("
"id INTEGER PRIMARY KEY AUTOINCREMENT,"
"name TEXT NOT NULL"
");",
"CREATE TABLE tasks ("
"id INTEGER PRIMARY KEY AUTOINCREMENT,"
"project_id INTEGER NOT NULL REFERENCES projects(id),"
"title TEXT NOT NULL"
");",
"CREATE TABLE comments ("
"id INTEGER PRIMARY KEY AUTOINCREMENT,"
"task_id INTEGER NOT NULL REFERENCES tasks(id),"
"body TEXT NOT NULL"
");",
"CREATE TABLE tags ("
"id INTEGER PRIMARY KEY AUTOINCREMENT,"
"label TEXT NOT NULL"
");"
}
}}
```
#### ❌ Wrong (form 1): one database per table
```c
// DO NOT do this. Four databases for one domain is wrong.
.databases = {
{.engine=sqlite_db, .name="projects_db", .connect="file:projects.db?mode=rwc",
.migrations={"CREATE TABLE projects (...);"}},
{.engine=sqlite_db, .name="tasks_db", .connect="file:tasks.db?mode=rwc",
.migrations={"CREATE TABLE tasks (...);"}},
{.engine=sqlite_db, .name="comments_db", .connect="file:comments.db?mode=rwc",
.migrations={"CREATE TABLE comments (...);"}},
{.engine=sqlite_db, .name="tags_db", .connect="file:tags.db?mode=rwc",
.migrations={"CREATE TABLE tags (...);"}}
}
```
#### ❌ Wrong (form 2): parent and child split into separate databases
This is subtler and the most common failure mode. The model "knows" to
group related tables, gets *projects* + *tasks* together in
`projects_db`, then **also** creates a `tasks_db` because tasks "feel
like a separate concept." Every line in this snippet is a Rule 2
violation:
```c
// DO NOT do this. Tasks belong to projects → ONE db, two migrations.
.databases = {
{.engine=sqlite_db, .name="projects_db", .connect="file:projects.db?mode=rwc",
.migrations={
"CREATE TABLE projects (...);",
"CREATE TABLE tasks (...);" // tasks already correctly here
}},
{.engine=sqlite_db, .name="tasks_db", .connect="file:tasks.db?mode=rwc",
.migrations={
"CREATE TABLE tasks (...);" // ❌ duplicate — tasks already exists above
}}
}
// And then the query reaches for the wrong db:
query(
{.set_key="project", .db="projects_db", .query="..."},
{.set_key="tasks", .db="tasks_db", .query="..."} // ❌ should be projects_db
)
```
> **Parent-child relationships are ONE domain, ONE database.** A project
> and its tasks, a blog and its comments, an order and its line items,
> a user and its sessions, a todo and its comments — these are all
> parent-child relations within a single domain. They live as separate
> **migrations on the same database**, joined later via `join()`.
> Splitting them across `projects_db` + `tasks_db` (or `blogs_db` +
> `comments_db`, etc.) is **wrong** — both ❌ examples above show why.
#### Rationalizations to recognize and REJECT
The model talks itself into Rule 2 violations using familiar-sounding
reasoning. Each of these is wrong:
- *"Projects and tasks are different concepts, so they should be
different domains."* → **Wrong.** A parent-child relation is by
definition ONE domain. The relation IS the thing that makes them
one domain.
- *"Separating tables by entity is cleaner / more normalized / better
separation of concerns."* → **Wrong in MACH.** The framework's unit
of separation is the **module**, not the table. Splitting one
module's tables across multiple databases doesn't add separation,
it adds duplication and cross-db query friction.
- *"Microservices use one database per service, so I should use one
database per table."* → **Wrong analogy.** In MACH, the equivalent
of "service" is **module**, not "table." One module = one database.
- *"My data model has X different entities, so I need X databases."*
→ **Wrong.** Number of databases = number of modules, not number of
entities. A module typically owns 3–10 tables.
> **Self-check before adding a second `.databases` entry:** "Am I
> introducing a new module?" If no, you don't need a new database —
> add a migration to the existing one. If yes, the new module gets
> its own one db (with however many tables it owns).
**Where the boundary actually goes.** A new database appears when a new
**module** appears, because each module owns its domain. The `todos`
module has one `todos_db` (containing `todos`, `comments`, `daily_stats`,
etc.). The `activity` module has its own `activity_db`. The `billing`
module has `billing_db`. One database per domain, one domain per module.
A new database appears with a new module, **not** with a new table.
Migrations are an array on the same database; they run in order, so a
later table can reference an earlier one with `REFERENCES`.
#### ✅ Canonical worked snippet — project + tasks pipeline (copy this shape)
This is the exact pattern for "show one parent and its children." If
you're writing anything that fits this shape (project + tasks, blog +
comments, order + line items, user + sessions), copy this snippet's
structure and rename.
```c
#include
#include
config mach(){
return (config){
.resources = {
{"project", "/projects/:id",
.get = {
validate({"id", .validation = validate_integer,
.message = "must be an integer"}),
// Rule 3: ONE step, TWO items, SAME db (Rule 2: parent + child = same domain).
query(
{.set_key = "project", .db = "projects_db",
.query = "select id, name from projects where id = {{id}};"},
{.set_key = "tasks", .db = "projects_db", // ← SAME db
.query = "select id, project_id, title from tasks where project_id = {{id}};"}
),
join(
.target_table_key = "project",
.target_field_key = "id",
.nested_table_key = "tasks",
.nested_field_key = "project_id",
.target_join_field_key = "tasks"
),
// Rule 1: open {{#project}} first; tasks lives INSIDE it after join.
render(.template =
"{{#project}}"
"
{{name}}
"
"
Tasks
"
"
{{#tasks}}
{{title}}
{{/tasks}}
"
"{{/project}}")
}
}
},
// Rule 2: ONE db for the projects domain. TWO migrations.
.databases = {{
.engine = sqlite_db,
.name = "projects_db",
.connect = "file:projects.db?mode=rwc",
.migrations = {
"CREATE TABLE projects ("
"id INTEGER PRIMARY KEY AUTOINCREMENT,"
"name TEXT NOT NULL"
");",
"CREATE TABLE tasks ("
"id INTEGER PRIMARY KEY AUTOINCREMENT,"
"project_id INTEGER NOT NULL REFERENCES projects(id),"
"title TEXT NOT NULL"
");"
}
}},
.modules = {sqlite} // ← REQUIRED. The sqlite bundled module must be
// registered for SQLite databases to work.
// Do NOT remove this line "for brevity" or
// assume some other file handles it. Every
// bundled module you use (sqlite, postgres,
// htmx, datastar, session_auth, etc.) must
// be listed here.
};
}
```
Every piece labeled. Every rule satisfied. If you're about to write
something similar and your version has a second `.databases` entry, or
two configs that aren't connected via `.modules`, or a `{{project.name}}`
in the template, or a missing `.modules = {sqlite}` line — your version
is wrong, this one is right. Reshape yours to match.
---
### Rule 3 — Concurrent queries: ONE step, MANY items (across databases too)
`query()` and `fetch()` run their items **in parallel**. Two separate
`query()` steps run **serially**. Whenever you need more than one query
or fetch and they don't depend on each other's results, put them in
**one** step. This works **even when the items hit different databases**.
#### ✅ Concurrent — one `query()` call with multiple items
Same database:
```c
query(
{.set_key = "todos", .db = "todos_db", .query = "select id, title from todos;"},
{.set_key = "count", .db = "todos_db", .query = "select count(*) as n from todos;"}
)
```
**Across multiple databases — still one step, still concurrent:**
```c
query(
{.set_key = "user", .db = "users_db", .query = "select * from users where id = {{id}};"},
{.set_key = "orders", .db = "commerce_db", .query = "select * from orders where user_id = {{id}};"},
{.set_key = "activity", .db = "activity_db", .query = "select * from events where user_id = {{id}};"}
)
```
Same rule for `fetch()`:
```c
fetch(
{"https://api.x.dev/a", .set_key = "a"},
{"https://api.y.dev/b", .set_key = "b"}
)
```
#### ❌ Serial — multiple steps, each waiting for the previous
```c
// DO NOT do this when the queries are independent. Three round-trips, in series.
query({.set_key = "user", .db = "users_db", .query = "..."}),
query({.set_key = "orders", .db = "commerce_db", .query = "..."}),
query({.set_key = "activity", .db = "activity_db", .query = "..."})
```
Use separate steps **only** when a later query depends on a value the
earlier query produced. Otherwise: one step, many items.
---
### Rule 4 — SQL `{{values}}` are bound as prepared-statement parameters
In `query()` and `find()`, `{{interpolation}}` is **bound as a parameter**,
never spliced into the SQL string. SQL injection is impossible at the
framework level. Do not pre-quote, do not pre-escape.
```c
✅ query({.db = "db", .query = "insert into todos(title) values({{title}});"})
❌ query({.db = "db", .query = "insert into todos(title) values('{{title}}');"}) // double-quoted
```
For transactions, use `BEGIN` / `COMMIT` / `ROLLBACK` directly in your queries.
---
### Rule 5 — Each `query()` / `find()` item: positional asset name **OR** `.query`. Pick exactly one. The asset name must actually exist.
There are two ways to supply SQL to a query item. Pick **exactly one**
per item, and if you pick the positional asset-name form, the name
must reference an asset that **actually exists** in `.context`.
```c
✅ query({.set_key = "todos", .db = "todos_db",
.query = "select id, title from todos;"})
// SQL inlined. No .context entry needed. Works in any snippet.
✅ query({"get_todos", .set_key = "todos", .db = "todos_db"})
// SQL loaded by name from .context. Requires the asset to be defined:
// .context = {{"get_todos", (asset){#embed "get_todos.sql"}}}
// Without that .context entry, this is a phantom reference (see ❌ below).
❌ query({"get_todos", .set_key = "todos", .db = "todos_db",
.query = "select ..."})
// BOTH forms in one item → boot rejection.
❌ query({"get_todos", .set_key = "todos", .db = "todos_db"})
// The name "get_todos" is positional asset reference, but no
// .context = {{"get_todos", (asset){#embed "..."}}} entry exists
// anywhere in the config. The query has NO SQL to run. Boot
// rejection / runtime failure. (Same shape as the ✅ above — the
// ONLY difference is whether .context defined the asset.)
```
> **If your config does not have a `.context` section that embeds SQL
> files, you MUST use inline `.query`.** The two forms are not
> interchangeable; the positional form is shorthand that says "this
> name was already embedded as an asset elsewhere in the config".
>
> The asset-name form is a Step-8 optimization (see Guide §8 "External
> Assets") for when SQL grows too large to keep in the `.c` file. For
> any inline-only snippet, `.query` is the only valid form. Do not
> reach for the positional name to avoid writing the SQL string —
> that produces a phantom reference, not a working query.
The same rule applies to `find()` and to `render()` (asset name in
`.context` vs `.template` inline string).
---
### Rule 6 — `find()` raises `http_not_found` on zero rows, `query()` does not
Otherwise the two are identical. Use `find()` for "must exist" lookups
(detail pages, by-id reads). Use `query()` for lists, counts, writes,
and anything where zero rows is a normal outcome.
---
### Rule 7 — No `malloc` / `free`, no threads, no mutexes, no locks
Per-request arena handles all memory. Reactors and the shared thread pool
handle all concurrency. Application code never calls these.
For a buffer in a pipeline: `char *buf = allocate(256);` (reclaimed when
the request ends). To clean up a pointer returned by an external library:
`defer_free(out);` (cleanup runs when the arena releases).
---
### Rule 8 — Resource-based, not route-based
Resources are referenced by **name**, never by hard-coded path:
```c
{{url:todos}} // → /todos
{{url:todo:5}} // → /todos/5 (literal arg)
{{url:todo:id}} // → /todos/{id from context}
redirect("todo:{{id}}") // 302 to /todos/{id}
reroute("todos") // re-enter pipeline server-side, same request
```
Changing `/todos` to `/items` later means changing one `.url` field.
Every link, redirect, and reroute follows.
---
## C SYNTAX PATTERNS — MACH expects standard C23 idioms
Three C-language patterns trip up small models even when MACH semantics
are correct. Get these wrong and the snippet **will not compile**, no
matter how perfectly it follows Rules 1–8. If your output looks
semantically right but doesn't match these three patterns, fix it.
### Pattern 1 — Adjacent string literals concatenate. One quoted line per source line.
C joins adjacent string literals at compile time. Use this idiom for
**every** multi-line SQL statement and **every** inline template. Do
NOT put a raw newline inside a single quoted string. Do NOT mix quoted
text and bare text on the same line.
```c
✅ "CREATE TABLE projects (" // each source line is its own
"id INTEGER PRIMARY KEY," // properly terminated quoted string
"name TEXT NOT NULL" // C concatenates them automatically
");"
❌ "CREATE TABLE projects ( // ← raw newline inside string = compile error
id INTEGER PRIMARY KEY,
name TEXT NOT NULL
);"
❌ "CREATE TABLE projects ("
id INTEGER PRIMARY KEY, // ← bare identifier, not in any string
name TEXT NOT NULL
");"
```
The exact same rule applies to inline templates — including the
Mustache section markers:
```c
✅ render(.template =
"{{#project}}" // every fragment is a quoted
"
// ← bare HTML, not a string
{{/tasks}} // ← bare Mustache, not a string
" // ← stray closing quote opens nothing
"{{/project}}")
```
The mental model: a MACH inline template is **not** a heredoc. It is a
pile of small C string literals that the compiler glues together. Every
fragment, every section marker, every literal HTML scrap must be inside
its own `"..."`.
### Pattern 2 — Don't quote SQL column/table names with `"..."`; it collides with C string delimiters
Standard SQL allows quoting identifiers with double quotes, but MACH
embeds SQL inside C strings, so a `"` inside the SQL ends the C string.
```c
✅ "CREATE TABLE projects (id INTEGER PRIMARY KEY, name TEXT NOT NULL);"
❌ "CREATE TABLE projects (\"id\" INTEGER PRIMARY KEY, \"name\" TEXT NOT NULL);"
// ↑ technically works (escaped), but unnecessary
❌ "CREATE TABLE projects ("id" INTEGER PRIMARY KEY, "name" TEXT NOT NULL);"
// ↑ this " closes the C string immediately — broken
```
SQLite, Postgres, and MySQL all accept unquoted identifiers for normal
column and table names. **Never quote identifiers in MACH SQL** unless
the identifier is a SQL reserved word — and even then, escape with
`\"`, not bare `"`.
### Pattern 3 — All top-level config fields go INSIDE the same `(config){...}` block, comma-separated
The single most common structural bug: prematurely closing the
`(config){...}` initializer, then trying to add more fields after it.
```c
✅ config mach(){
return (config){
.resources = {...}, // comma between fields
.databases = {{...}}, // comma between fields
.modules = {sqlite} // last field — no trailing comma needed
}; // ONE closing brace + ONE semicolon
}
❌ config mach(){
return (config){
.resources = {...}
}; // ← THIS ends the return statement
// everything below is dead code
.databases = {{...}}; // ← outside any expression: compile error
.modules = {sqlite};
}
```
**Brace count check.** In the ✅ form there is exactly **one**
`(config){...}` initializer, opened once and closed once. Every
top-level field — `.resources`, `.databases`, `.modules`, `.events`,
`.tasks`, `.publishes`, `.context`, `.errors`, `.repairs` — goes
inside that single block, separated by commas. If your snippet has
two `};` near the end of `mach()`, you've broken the structure.
### Self-check before emitting any snippet
Three quick passes over your generated code:
1. **Strings:** does every line of every multi-line SQL or template
start with `"` and end with `"`? Are there any raw newlines inside
a string, or any bare HTML/SQL tokens between strings?
2. **SQL quotes:** are any column or table names wrapped in `"..."`?
Remove the quotes (or escape with `\"`).
3. **Brace count:** is there exactly one `};` at the end of `mach()`,
closing one `(config){...}` initializer? Are all `.fields` inside
that one block, comma-separated?
If any check fails, the snippet won't compile. Fix it before returning.
---
## Guide
A todo app, built one concept at a time. Each step shows only the new
pieces; carry forward the previous code.
### 1. A Page
Two resources, each with a GET pipeline. `{{url:name}}` resolves at render time.
```c
#include
config mach(){
return (config) {
.resources = {
{"home", "/",
.get = { render(.template =
"
") }
}
}
};
}
```
### 2. Show Data
Add SQLite. `query()` stores rows under `todos`. The template opens the
section to iterate (Rule 1: section, never dot).
```c
#include
// inside todos resource:
.get = {
query({.set_key = "todos", .db = "todos_db",
.query = "select id, title from todos;"}),
render(.template =
"
My Todos
"
"
{{#todos}}
{{title}}
{{/todos}}
")
}
// inside config:
.databases = {{
.engine = sqlite_db,
.name = "todos_db",
.connect = "file:todos.db?mode=rwc",
.migrations = {
"CREATE TABLE todos ("
"id INTEGER PRIMARY KEY AUTOINCREMENT,"
"title TEXT NOT NULL"
");"
},
.seeds = {"INSERT INTO todos(title) VALUES('Learn MACH');"}
}},
.modules = {sqlite}
```
To fetch two things at once, put both items in **one** `query()` call (Rule 3):
```c
query(
{.set_key="todos", .db="todos_db", .query="select id, title from todos;"},
{.set_key="count", .db="todos_db", .query="select count(*) as n from todos;"}
)
```
### 3. Accept Input
`validate()` → `query()` → `redirect()` (POST-redirect-GET). On success
`title` is promoted from `input:title` to app scope and bound as a
prepared parameter (Rule 4) in the SQL.
```c
.post = {
validate({"title",
.validation = validate_not_empty,
.message = "title cannot be empty"}),
query({.db = "todos_db",
.query = "insert into todos(title) values({{title}});"}),
redirect("todos")
}
```
Add the form to the GET template; `{{input:title}}` repopulates after errors:
```html
```
### 4. Handle Errors
A failed `validate()` raises `http_bad_request`. A resource-scoped error
handler re-enters the GET pipeline with `reroute()`. Both `input:` and
`error:` scopes survive the reroute.
```c
.errors = {
{http_bad_request, { reroute("todos") }}
}
```
```html
{{#error:title}}{{error_message:title}}{{/error:title}}
```
### 5. Nested Data
Fetch parent + children **concurrently** in one `query()` (Rule 3),
`join()` to nest, then enter the parent section to render. Comments
belong to the same domain as todos, so `comments` is a new **migration**
on the existing `todos_db` (Rule 2), not a new database.
```c
{"todo", "/todos/:id",
.get = {
validate({"id", .validation = validate_integer,
.message = "must be an integer"}),
query(
{.set_key = "todo", .db = "todos_db",
.query = "select id, title from todos where id = {{id}};"},
{.set_key = "comments", .db = "todos_db",
.query = "select id, todo_id, body from comments where todo_id = {{id}};"}
),
join(
.target_table_key = "todo",
.target_field_key = "id",
.nested_table_key = "comments",
.nested_field_key = "todo_id",
.target_join_field_key = "comments"
),
render(.template =
"{{#todo}}"
"
{{title}}
"
"
{{#comments}}
{{body}}
{{/comments}}
"
"{{/todo}}")
}
}
```
After `join()`, `comments` lives **inside** each `todo` record. Reach it
from within `{{#todo}}`. Iterating `{{#comments}}` at root after a join
renders nothing.
### 6. Tasks
Tasks run async on task reactors. Trigger with `task("name")` or via
`.cron`. Same task can be both. Tasks are **durable**: the process can
crash mid-task and resume at the failed step on next boot.
```c
// in POST pipeline:
.post = {
validate({...}),
query({...}),
task("record_daily_stats"),
redirect("todos")
}
// at config level:
.tasks = {
{"record_daily_stats", {
query({.db = "todos_db",
.query = "insert into daily_stats(todo_count) "
"select count(*) from todos;"})
}, .cron = "0 0 * * *"}
}
```
If the task needs caller context, list keys under `.accepts`:
```c
{"recount_for_user", {
query({.db="todos_db", .query="update users set ... where id = {{user_id}};"})
}, .accepts = {"user_id"}}
```
### 7. Modules & Events
A module is a `.c` file with a function returning `config`. It owns its
own resources, **its own database** (one per domain — Rule 2),
migrations, tasks, and event subscribers. Modules communicate **only**
through pub/sub events, never direct calls. `main.c` includes them and
registers them under `.modules`.
```
.
├── todos/todos.c // config todos() { ... }
├── activity/activity.c // config activity() { ... }
└── main.c
```
**`main.c`**:
```c
#include
#include
#include "todos/todos.c"
#include "activity/activity.c"
config mach(){
return (config){
.resources = {{"home", "/", .get = { render(.template = "
Welcome
") }}},
.modules = {todos, activity, sqlite}
};
}
```
**Publisher** declares `.publishes` and calls `emit()`:
```c
config todos(){
return (config){
.name = "todos",
.publishes = {{"todo_created", .with = {"title"}}},
.resources = {
{"todos", "/todos",
.post = {
validate({"title", .validation = validate_not_empty}),
query({.db = "todos_db",
.query = "insert into todos(title) values({{title}});"}),
emit("todo_created"),
redirect("todos")
}
}
}
// ... own database (todos_db) here
};
}
```
**Subscriber** declares an `.events` entry. Published keys (`title`)
arrive in context. Subscriber owns its own database (`activity_db`).
```c
config activity(){
return (config){
.name = "activity",
.events = {
{"todo_created", {
query({.db = "activity_db",
.query = "insert into activities(kind, ref) "
"values('created', {{title}});"})
}}
}
// ... own database (activity_db) here
};
}
```
When `.publishes` exists anywhere, MACH creates a `mach_events` database
and tracks delivery. Undelivered events replay on next boot.
### 8. External Assets
Once templates and SQL grow, extract them into files. Embed with
`(asset){#embed "file"}` in `.context`, then reference by name from
`render()`, `query()`, and `find()`. `.migrations` accepts assets directly.
```
todos/
├── todos.c
├── todos_list.mustache.html
├── get_todos.sql
├── create_todo.sql
└── create_todos_table.sql
```
**`todos/get_todos.sql`**
```sql
select id, title from todos;
```
**`todos/todos.c`** (excerpt):
```c
.resources = {
{"todos", "/todos",
.get = { query({"get_todos", .set_key = "todos", .db = "todos_db"}),
render("todos_list") },
.post = { validate({"title", .validation = validate_not_empty}),
query({"create_todo", .db = "todos_db"}),
redirect("todos") }
}
},
.context = {
{"todos_list", (asset){#embed "todos_list.mustache.html"}},
{"get_todos", (asset){#embed "get_todos.sql"}},
{"create_todo",(asset){#embed "create_todo.sql"}}
},
.databases = {{
.engine = sqlite_db,
.name = "todos_db",
.connect = "file:todos.db?mode=rwc",
.migrations = {(asset){#embed "create_todos_table.sql"}}
}}
```
SQL `{{interpolation}}` works the same as inline (still parameter-bound).
### 9. External Data
`fetch()` makes an HTTP request and stores the response in context.
JSON is parsed into tables/records (nested JSON → nested context tables);
plain text stores as a string.
```c
.get = {
fetch("https://api.quotable.io/random", .set_key = "quote"),
render("home")
}
```
The Quotable API returns `{"author":"...","content":"..."}`, parsed into
a single-row table under `quote`. Template opens the section (Rule 1):
```html
{{#quote}}
{{content}}, {{author}}
{{/quote}}
```
Multiple items in one `fetch()` run concurrently, same as `query()`.
`fetch()` supports POST/PUT/PATCH/DELETE, custom headers, JSON or text
bodies, and `{{interpolation}}` in URLs.
---
## Reference
### Notation
- `{}` — single value or struct: `.get = { ... }`
- `{{}}` — array of structs: `.databases = {{ ... }}`
- Multiple elements: `.databases = {{...}, {...}}`
- Multiple step items: `query({...}, {...})`
### Context
Per-request scoped key-value store. Three scopes:
- `input:xxx` — raw request parameters
- `error:xxx` — validation/error data
- (unprefixed) — app scope: query results, validated inputs, `.context` values
`validate()` promotes from `input:` to app scope. Docker secrets land in
context. `.context` seeds variables and assets at the root. Assets baked
at compile time via `(asset){#embed "file"}`.
```c
.context = {
{"site_name", "MACH App"},
{"layout", (asset){#embed "static/layout.mustache.html"}},
{"get_todos", (asset){#embed "todos/get_todos.sql"}}
}
```
### Databases
Migrations are forward-only, index-based, applied once each in array
order, tracked in `mach_meta`. Seeds are idempotent. Multi-tenant via
`{{interpolation}}` in `.connect`; connections pooled with LRU eviction.
**Reminder (Rule 2): one database per domain, many tables.** Related
tables go as separate migrations on the same database.
```c
.databases = {{
.engine = sqlite_db,
.name = "blog_db",
.connect = "file:{{user_id}}_blog.db?mode=rwc", // multi-tenant
.migrations = {
"CREATE TABLE blogs ("
"id INTEGER PRIMARY KEY AUTOINCREMENT,"
"title TEXT NOT NULL,"
"content TEXT NOT NULL"
");",
"CREATE TABLE comments ("
"id INTEGER PRIMARY KEY AUTOINCREMENT,"
"blog_id INTEGER NOT NULL REFERENCES blogs(id),"
"body TEXT NOT NULL"
");"
},
.seeds = {"INSERT OR IGNORE INTO blogs(id, title, content) VALUES(1, 'Hi', 'First');"}
}}
```
**Engines:** `sqlite_db`, `postgres_db`, `mysql_db`, `redis_db`, `duckdb_db`
### Resource Pipelines
Each `.resources` entry is a named URL endpoint. Identified by name in
`{{url:name}}`, `redirect()`, `reroute()` with colon-separated positional
args (`name:arg1:arg2`) that fill `:params` in URL-pattern order. Args
can be literals or context keys.
- `{{url:todos}}` → `/todos`
- `{{url:todo:5}}` → `/todos/5` (literal)
- `{{url:todo:id}}` → reads `id` from current scope
- `{{url:org_todo:acme:5}}` → fills multiple `:params`
Path specificity is automatic: `/todos/active` beats `/todos/:id`. Verb
selection: HTTP method, or `?http_method=...` parameter (lets HTML forms
reach PATCH/DELETE/SSE).
**Fields:**
- `.name` *(pos)* — identifier
- `.url` *(pos)* — pattern with `:params`
- `.steps` *(pos)* — shared steps run before every verb (middleware slot)
- `.mime` — default response content type
- `.get .post .put .patch .delete` — verb pipelines (arrays of steps)
- `.sse` — persistent SSE channel; first positional is channel name
- `.errors` — terminal handlers keyed by error code
- `.repairs` — resumable handlers keyed by error code
```c
{"todo", "/todos/:id", {
validate({"id", .validation = "^\\d+$", .message = "must be a number"})
},
.mime = mime_html,
.get = { find({"get_todo", .set_key = "todo", .db = "todos_db"}),
render("todo") },
.patch = { validate({"title", .validation = validate_not_empty, .message = "required"}),
query({.db = "todos_db",
.query = "update todos set title = {{title}} where id = {{id}};"}),
redirect("todo:{{id}}") },
.delete = { query({.db = "todos_db",
.query = "delete from todos where id = {{id}};"}),
redirect("todos") },
.sse = {"todo/{{id}}", sse(.event = "ready") },
.errors = {{http_not_found, { render("404") }}}
}
```
**MIME types:** `mime_html`, `mime_txt`, `mime_sse`, `mime_json`, `mime_js`
### Template Helpers
`{{helper:args}}` — positional, **colon-separated** (not dot-separated).
Each arg is a literal or a context key.
| Helper | Purpose | Example |
|---|---|---|
| `{{raw:field}}` | emit without HTML-escape (default escapes) | `
{{raw:body_html}}
` |
| `{{precision:field:N}}` | numeric format with N decimals | `${{precision:total:2}}` |
| `{{input:field}}` | raw request param (form repopulation) | `` |
| `{{error:field}}` | truthy when field has an error (use as section) | `{{#error:title}}!{{/error:title}}` |
| `{{error_message:field}}` | the validation/error message | `{{error_message:title}}` |
| `{{error_code:field}}` | HTTP status code for the field error | `{{error_code:title}}` |
| `{{url:name[:args]}}` | resource URL by name with positional args | `...` |
| `{{asset:filename}}` | cache-busted URL for `public/` file | `` |
| `{{csrf:token}}` | CSRF token (for query strings); sets cookie | `?csrf={{csrf:token}}` |
| `{{csrf:input}}` | hidden `` carrying CSRF token | `` |
CSRF verification is automatic: MACH compares the incoming token to the
cookie (httponly/secure/samesite) and returns 403 on mismatch. Just emit
`{{csrf:token}}` or `{{csrf:input}}`.
### Pipeline Steps
Every step accepts `.if_context` and `.unless_context`.
#### validate
Regex-checks request parameters. On success, promotes `input:name` to
app scope. On failure, sets `error:name` and raises `http_bad_request`.
All validations in one call complete before the error fires (so all
errors arrive together for form re-rendering). Define your own:
`#define validate_zipcode "^\\d{5}$"`.
- `.param_key` *(pos)* — name of param
- `.validation` — regex string or built-in macro
- `.message` — human-readable error
- `.optional` — skip when param absent
- `.fallback` — default when param absent
```c
validate(
{"email", .validation = validate_email, .message = "must be a valid email"},
{"title", .validation = validate_not_empty, .message = "cannot be empty"},
{"page", .fallback = "1",
.validation = "^\\d+$", .message = "must be a number"},
{"filter", .optional = true,
.validation = "^(active|done)$", .message = "must be active or done"}
)
```
**Built-in validators:**
- Strings: `validate_not_empty`, `validate_alpha`, `validate_alphanumeric`, `validate_slug`, `validate_no_html`
- Numbers: `validate_integer`, `validate_positive`, `validate_float`, `validate_percentage`
- Identity: `validate_email`, `validate_uuid`, `validate_username`
- Dates: `validate_date`, `validate_time`, `validate_datetime`
- Web: `validate_url`, `validate_ipv4`, `validate_hex_color`
- Codes: `validate_zipcode_us`, `validate_phone_e164`, `validate_cron`
- Security: `validate_no_sqli`, `validate_token`, `validate_base64`
- Boolean: `validate_boolean`, `validate_yes_no`, `validate_on_off`
#### find & query
Both run database queries. **`find()` raises `http_not_found` on zero
rows; `query()` does not.** Otherwise identical.
> **Before emitting any `query()` / `find()` item, run the Rule 5
> check.** Each item supplies SQL exactly one way:
> - **Inline `.query = "select ..."`** — works in any snippet, no
> `.context` setup required. Use this by default.
> - **Positional asset name `{"get_todos", ...}`** — only valid if
> `.context` actually defines `"get_todos"` as an embedded asset.
> Without that entry, the query has no SQL and will fail.
>
> If your config has no `.context` section, `.query` is the only valid
> form. Do not type a positional name to "tidy up" — that produces a
> phantom reference, not a working query.
`.set_key` stores the result as a **table** in context (always — even
single-row results, see Rule 1 Pattern B). Templates open the table as
a section to access fields. SQL is either inlined with `.query` OR
loaded by name from `.context` as the positional (Rule 5). Multiple
items in one step run **concurrently** (Rule 3), even across different
databases. Interpolated `{{values}}` are bound as prepared parameters
(Rule 4). For transactions: `BEGIN`/`COMMIT`/`ROLLBACK` in the SQL.
- `.template_key` *(pos)* — SQL asset name in `.context` (vs `.query`)
- `.query` — inline SQL string with `{{interpolation}}` (vs positional)
- `.set_key` — context key for result table
- `.db` — database name from `.databases`
- `.if_context` / `.unless_context` *(per item)* — conditionally include
while other items run concurrently
```c
query(
{"get_todos", .set_key = "todos", .db = "todos_db"},
{.set_key = "count", .db = "todos_db",
.query = "select count(*) as n from todos where user_id = {{user_id}};"},
{.if_context = "show_urgent", .set_key = "urgent", .db = "todos_db",
.query = "select id, title from todos where priority = 'high';"}
)
```
#### join
Nests records from one context table into each matching record of
another, in memory. After `join()`, the inner records live **inside**
each outer record. Templates must enter the outer section to reach the
nested data. `{{#comments}}` at root after a join is empty.
- `.target_table_key` — outer table receiving children
- `.target_field_key` — outer field to match
- `.nested_table_key` — inner table to nest
- `.nested_field_key` — inner field that points to outer
- `.target_join_field_key` — new field on outer holding matched inner records
Pattern: concurrent `query()` → `join()` → `render()`:
```c
query(
{.set_key="blog", .db="blog_db", .query="select id, title from blogs where id = {{id}};"},
{.set_key="comments", .db="blog_db", .query="select id, blog_id, body from comments where blog_id = {{id}};"}
),
join(
.target_table_key="blog", .target_field_key="id",
.nested_table_key="comments", .nested_field_key="blog_id",
.target_join_field_key="comments"
),
render(.template =
"{{#blog}}"
"
{{title}}
"
"
{{#comments}}
{{body}}
{{/comments}}
"
"{{/blog}}")
```
Context shape:
```
after query(): { blog: [{id,title}], comments: [{id,blog_id,body}, ...] }
after join(): { blog: [{id,title, comments: [{id,blog_id,body}, ...]}] }
```
#### fetch
HTTP request → context. JSON parsed into tables/records; text stored as
string. Multiple items in one step run concurrently.
- `.url` *(pos)* — URL with `{{interpolation}}`
- `.set_key` — context key for response
- `.method` — defaults `http_get`
- `.headers` — array of `{name, value}` pairs
- `.json` — context key serialized as JSON request body
- `.text` — context key sent as plain-text body
```c
fetch("https://api.payments.dev/charge",
.set_key = "receipt",
.method = http_post,
.headers = {
{"Authorization", "Bearer {{api_key}}"},
{"Idempotency-Key", "{{order_id}}"}
},
.json = "order"
)
```
**HTTP methods:** `http_get`, `http_post`, `http_put`, `http_patch`, `http_delete`, `http_sse_method`
#### exec
Calls a C function or block with imperative access to context. Dispatched
to the shared thread pool (releases the reactor); pipeline resumes on
the original reactor when done. Use for blocking I/O or CPU work.
Trigger an error pipeline from inside via `error_set()`.
- *Block* *(pos)* — inline block
- `.call` — named C function
```c
exec(^(){
auto t = get("challengers");
record_set(table_get(t, 0), "opponent_id",
record_get(table_get(t, 1), "id"));
})
exec(.call = assign_opponents)
```
**Imperative API** (in exec blocks/functions):
- Context: `get(name)`, `set(name, value)`, `has(name)`, `format(fmt)`
- Memory: `allocate(bytes)`, `defer_free(ptr)`
- Errors: `error_set(name, err)`, `error_get(name)`, `error_has(name)`
- Tables: `table_new()`, `table_count(t)`, `table_get(t, i)`, `table_add(t, r)`, `table_remove(t, r)`, `table_remove_at(t, i)`
- Records: `record_new()`, `record_set(r, name, value)`, `record_get(r, name)`, `record_remove(r, name)`
#### emit
Triggers a pub/sub event. Subscribers in other modules react via their
`.events` pipelines.
```c
emit("todo_created")
```
#### task
Enqueues a named job in the task database; calling pipeline continues
immediately.
```c
task("recount_todos")
```
#### sse
Pushes a Server-Sent Event. With `.channel`, broadcasts. Without, sent
only to the requesting client.
- `.channel` *(pos)* — broadcast channel with `{{interpolation}}`
- `.event` — SSE `event:` line
- `.data` — array of strings (one per `data:` line)
- `.comment` — `:` comment line (keep-alives)
```c
sse(
.channel = "todos/{{user_id}}",
.event = "todo_updated",
.data = {"id: {{todo_id}}", "title: {{title}}"},
.comment = "broadcast at {{timestamp}}"
)
```
#### ds_sse
Datastar-formatted SSE; provided by `datastar` module. Pushes DOM updates
and reactive state. Without channel goes to requesting client; with
channel broadcasts.
- `.channel` *(pos)* — broadcast channel
- `.target` — DOM element id
- `.mode` — fragment insertion mode
- `.elements` — render_config (positional is asset name; supports `.template`, `.engine`)
- `.signals` — JSON updating Datastar reactive state
- `.js` — JS snippet evaluated on client
```c
ds_sse("todos/{{user_id}}",
.target = "todo-list",
.mode = mode_prepend,
.elements = {"todo_row"},
.signals = "{\"count\": {{count}}}",
.js = "window.scrollTo(0, 0)"
)
```
**Modes:** `mode_outer`, `mode_inner`, `mode_replace`, `mode_prepend`, `mode_append`, `mode_before`, `mode_after`, `mode_remove`
#### render
Outputs a Mustache template. Auto-escapes by default (`{{raw:field}}`
opts out). All field access follows Rule 1 — sections only, never dot.
> **Before emitting any `render(.template = ...)`, run the Template
> Checklist from Rule 1 against every `{{ ... }}` in the string.**
> Three checks per tag, in order:
> 1. No `.` between `{{` and `}}` — if there is, stop and add a section.
> 2. The bare name must be reachable from the current nesting level
> (root, or inside whichever `{{#section}}` you are currently in).
> 3. Number of `{{#...}}{{/...}}` wrappers = number of nesting levels
> between root and the field.
>
> **Same rule as Rule 5 applies to the template form itself:** use
> either the positional asset name (which must exist in `.context`)
> OR the inline `.template` string. If your config has no `.context`
> section embedding template files, use `.template` inline — do not
> reference a phantom asset name.
- `.template_key` *(pos)* — asset name in `.context`
- `.template` — inline Mustache string
- `.status` — HTTP status (default `http_ok`)
- `.mime` — override content type
- `.engine` — `mustache` (default) or `mdm` (Markdown-with-Mustache)
- `.json_table_key` — context table to serialize as JSON response
(sets `application/json`; nested tables → nested JSON)
```c
render("todos")
render(.template = "
{{site_name}}
")
render("not_found", .status = http_not_found)
render(.engine = mdm, .template = "# Welcome, {{user_name}}")
render(.json_table_key = "todos")
```
**HTTP statuses:** `http_ok` (200), `http_created` (201), `http_redirect` (302), `http_bad_request` (400), `http_not_authorized` (401), `http_not_found` (404), `http_error` (500)
#### headers & cookies
Set response headers/cookies. Values support `{{interpolation}}`.
```c
headers({{"X-Request-Id", "{{request_id}}"}, {"Cache-Control", "no-store"}})
cookies({{"session", "{{session_id}}"}})
```
#### redirect & reroute
`redirect()` sends a 302 to the client (browser navigates). `reroute()`
is server-side: re-enter the router and run another resource's pipeline
within the same request. Both take a resource identifier
`name[:arg1:arg2...]`. Args can be literals or context keys.
```c
redirect("todos") // 302 /todos
redirect("todo:5") // 302 /todos/5
redirect("todo:{{id}}") // 302 /todos/{id from context}
redirect("org_todo:acme:5") // 302 /orgs/acme/todos/5
reroute("todo:{{id}}") // run pipeline in-process
```
#### nest
Group steps under a single shared `.if_context` / `.unless_context`.
```c
nest({query({...}), emit("urgent_todo"), render("urgent")},
.if_context = "is_urgent")
```
### Conditionals
Every step accepts `.if_context` (run when key present) and
`.unless_context` (run when absent). Works on validated inputs, query
results, framework flags (`is_htmx`), or flags set from `exec()`.
```c
render("fragment", .if_context = "is_htmx")
render("full_page", .unless_context = "is_htmx")
// multi-state: set flag in exec, then key off it:
exec(.call = classify_todo),
render("urgent_confirmation", .if_context = "is_urgent"),
render("standard_confirmation", .unless_context = "is_urgent")
```
### Error and Repair Pipelines
On failure, MACH searches handlers bottom-up: resource → module → root.
- **Errors** are terminal: send a response, end the request.
- **Repairs** are resumable: fix context, then resume the original
pipeline at the step after the failure.
If no matching repair, falls through to errors. The `error` scope is
shared across `validate()` and `error_set()`: `{{error:name}}`,
`{{error_code:name}}`, `{{error_message:name}}`. Raw input remains in
`input:name`.
```c
.errors = {
{http_not_found, { render("404") }},
{http_bad_request, { render("form") }},
{http_error, { render("500") }}
},
.repairs = {
{http_not_authorized, { exec(.call = refresh_session_token) }}
}
```
**Built-in error codes:** `http_ok` (200), `http_created` (201),
`http_redirect` (302), `http_bad_request` (400), `http_not_authorized`
(401), `http_not_found` (404), `http_error` (500). Any int works;
`#define err_quota_exceeded 723` for domain-specific.
### Event Pipelines
Internal pub/sub for cross-module communication. Publisher doesn't know
subscribers; subscribers don't know publishers. Adding a subscriber =
new module with `.events`; publisher unchanged.
When `.publishes` exists anywhere, MACH creates `mach_events` to track
delivery. Crashes don't drop events; they replay on next boot.
- `.publishes` — outbound contracts: `.event` name, `.with` keys to pass
- `.events` — subscriber pipelines keyed by event name
```c
// publisher
config todos(){
return (config){
.name = "todos",
.publishes = {
{"todo_created", .with = {"user_id", "title"}},
{"todo_deleted", .with = {"user_id", "todo_id"}}
},
.resources = {
{"todos", "/todos",
.post = {
validate({"title", .validation = validate_not_empty}),
query({"insert_todo", .db = "todos_db"}),
emit("todo_created"),
redirect("todos")
}
}
}
};
}
// subscriber: owns its OWN database (Rule 2)
config activity(){
return (config){
.name = "activity",
.events = {
{"todo_created", {
query({.db = "activity_db",
.query = "insert into activities(kind, user_id, ref) "
"values('created', {{user_id}}, {{title}});"})
}}
}
};
}
```
### Task Pipelines
Named pipelines that run async on task reactors. Fire-and-forget. Defined
at module or root level. Triggered with `task("name")` or via `.cron`.
Tasks can enqueue more tasks.
Durable: `mach_tasks` checkpoints context after each step. Crash mid-task
→ resumes at the failed step.
- `.name` *(pos)* — identifier, called via `task("name")`
- `.accepts` — context keys to pull from caller into the task
- `.cron` — standard cron schedule (no caller required)
- *Steps* *(pos)* — pipeline body, second positional brace block
```c
.tasks = {
// on-demand
{"recount_todos", {
query({.db = "todos_db",
.query = "update users set todo_count = "
"(select count(*) from todos where user_id = users.id) "
"where id = {{user_id}};"})
}, .accepts = {"user_id"}},
// recurring
{"daily_digest", {
query({.db = "todos_db",
.query = "insert into digest_reports(generated_at) values(now());"}),
emit("digest_ready")
}, .cron = "0 8 * * *"}
}
```
### Modules & Composition
Every app and module returns a `config`. Root `main.c` defines `mach()`;
modules define their own functions with any name. A module owns its
resources, **its own database** (Rule 2: one per domain), migrations,
templates, and event contracts. **Same-name conflicts: root wins.**
Modules communicate ONLY through pub/sub events.
> **There are TWO different things both called "modules" — keep
> them straight:**
>
> 1. **User-defined modules** = `config foo(){...}` functions you
> write to split your own app into feature slices (a `projects`
> module, an `activity` module, etc.). For small / single-file
> snippets, **skip these** — put everything in `config mach()`
> directly. Defining one and not registering it under
> `.modules = {foo, ...}` makes it dead code; its resources and
> databases are not part of the running app.
>
> 2. **Bundled modules** = engine and feature modules shipped with
> MACH: `sqlite`, `postgres`, `mysql`, `redis`, `duckdb`, `htmx`,
> `datastar`, `tailwind`, `session_auth`. **These MUST be
> registered in `.modules` whenever you use what they provide.**
> A SQLite database needs `.modules = {sqlite}`. A Datastar SSE
> step needs `.modules = {datastar}`. Even a single-file snippet
> with one resource and one SQLite db needs `.modules = {sqlite}`
> — there is no implicit registration, ever.
>
> So "skip modules for small snippets" applies to **user-defined**
> modules only. The `.modules` field itself is not optional —
> whatever bundled modules your snippet uses must be listed there.
> Do not write a comment like *"omitting .modules for brevity,
> assumed elsewhere"* — there is no elsewhere; this is the file.
- `.name` — module identifier
- `.modules` — other modules to compose (root or nested)
A module file:
```c
#include
#include
config blogs(){
return (config){
.name = "blogs",
.resources = {
{"blog", "/blogs/:id",
.get = { /* validate → query → join → render */ }
}
},
.databases = {{
.engine = sqlite_db,
.name = "blog_db", // ONE db for the blogs domain
.connect = "file:blogs.db?mode=rwc",
.migrations = { // many tables, all in this db
"CREATE TABLE blogs (id INTEGER PRIMARY KEY AUTOINCREMENT, title TEXT NOT NULL, content TEXT NOT NULL);",
"CREATE TABLE comments (id INTEGER PRIMARY KEY AUTOINCREMENT, blog_id INTEGER NOT NULL REFERENCES blogs(id), body TEXT NOT NULL);"
}
}}
};
}
```
Bring it in from `main.c`:
```c
#include
#include "blogs/blogs.c"
config mach(){ return (config){ .modules = {blogs, sqlite} }; }
```
Resource fields like `.url`, `.mime`, `.get` belong **inside** entries of
`.resources`, not at the top level of `config`.
Project layout:
```
├── todos/ # todos module — owns todos_db
│ ├── todos.c
│ ├── todos.mustache.html
│ ├── create_todos_table.sql
│ └── get_todos.sql
├── activity/ # activity module — owns activity_db
│ └── activity.c
├── static/ # root-level templates (not a module, no .c)
│ └── home.mustache.html
├── public/ # static files served directly
│ └── favicon.png
└── main.c
```
**Bundled modules** (add to `.modules`): `sqlite`, `postgres`, `mysql`,
`redis`, `duckdb`, `htmx`, `datastar`, `tailwind`, `session_auth`
**Module-provided steps.** Modules can ship step functions that plug into
pipelines like built-ins. `session_auth` provides:
- `session()` — attaches current session to context (sets `user_id`,
etc.); no-op when unauthenticated
- `logged_in()` — guard, raises `http_not_authorized` if no session
- `login()`, `logout()`, `signup()` — for POST pipelines
Common as resource-level middleware via `.steps`:
```c
{"dashboard", "/dashboard", {session(), logged_in()},
.get = { render("dashboard") }
}
```
### Static Files
Files in `public/` at project root are served directly. Reference with
`{{asset:filename}}`, which resolves to a content-checksummed URL with
immutable cache headers.
```
public/
├── favicon.png
├── logo.png
└── styles.css
```
```html
```
### External Dependencies
Containerized dev environment; no local toolchain. Two ways to bring in
third-party C libraries, plus two memory bridges.
**`/vendor` directory** — drop in headers and `.so`/`.a`; auto-compiler
discovers, includes, and links them.
```
/vendor/
├── libsodium.h
└── libsodium.so
```
**Custom Dockerfile** — inherit from MACH base image, `apt-get` system
deps; reference from `compose.yml`.
```dockerfile
FROM mach:latest
RUN apt-get update && apt-get install -y libsodium-dev
```
**`allocate(bytes)`** — buffer from pipeline arena, reclaimed on request
completion.
```c
char *buf = allocate(256);
```
**`defer_free(ptr)`** — schedule cleanup for pointers from external libs
(`malloc`, etc.) when the arena is released.
```c
char *out = third_party_alloc(256);
defer_free(out);
```
---
## Architecture (brief)
- **Boot once.** `mach()` runs once at boot. The returned `config` is
compiled into an execution graph with prepared queries and templates.
- **Multi-reactor.** Request reactors handle HTTP (one per CPU). Task
reactors handle background jobs (one per CPU). Shared thread pool
handles `exec()` and blocking I/O.
- **Memory.** Per-request arena allocators. No `malloc`/`free` in app
code. Arena cleared on request end. Pipelines exceeding 5MB (default,
configurable) abort with a 500.
- **Safety by default.** SQL injection prevented by parameter binding
(Rule 4). XSS prevented by `render()` auto-escape; opt out with
`{{raw:field}}`. CSRF prevented by `{{csrf:token}}` / `{{csrf:input}}`.
- **Tooling.** TUI editor with HMR/LSP/AI; `app_info`, `unit_tests`,
`e2e_tests`, `app_debug`, `app_build` commands; OpenTelemetry on :4000.
---
## Final reminder — the rules a small model breaks most often
1. **No dot in `{{ }}`.** Every nested access is a section. Run the
Template Checklist (Rule 1) on every tag. (Rule 1)
2. **One database per domain, many tables. A "domain" = what one
MODULE owns, not a noun in your data model.** Parent + child
(project + tasks, blog + comments) is **one** domain, **one** db,
**two migrations**. Before adding a second `.databases` entry, ask:
"am I adding a new module?" If no, don't. (Rule 2)
3. **Concurrent = ONE step, MANY items.** Even across databases. (Rule 3)
4. **Asset name OR `.query`, never both.** AND the asset name must
actually exist in `.context`. If your snippet has no `.context`,
use inline `.query`. Don't reference phantom assets. (Rule 5)
5. **`join()` moves children.** After `join(tasks → project)`, `tasks`
no longer exists at root. Open `{{#project}}` first. (Rule 1, Pattern C)
6. **There are TWO things called "modules." Don't conflate them.**
- **User-defined** (`config foo(){...}`): for splitting your app
into features. Skip these for small snippets — write everything
in `config mach()`. If you do define one, register it under
`.modules` or it's dead code.
- **Bundled** (`sqlite`, `postgres`, `htmx`, `datastar`, etc.):
**MUST** be in `.modules` whenever you use what they provide.
A SQLite database needs `.modules = {sqlite}` even in a
single-file snippet. The `.modules` field is never optional.
Never write *"omitting .modules for brevity"* — there is no
"elsewhere" to register it.
7. **C syntax matters.** Multi-line SQL and templates are ADJACENT
QUOTED STRING LITERALS, one per source line — not heredocs, not
bare text between quotes. Don't double-quote SQL identifiers
(collides with C `"`). All `.fields` go inside ONE `(config){...}`
block, comma-separated, closed by ONE `};`. (See **C Syntax
Patterns** section.)
If you catch yourself writing `{{a.b}}`, declaring `projects_db` +
`tasks_db` for one domain (or any parent + child split across two dbs),
chaining three independent `query({...})` steps, naming an asset
(`{"get_todos", ...}`) that you never embedded in `.context`, defining
a `config foo()` you never registered under `.modules`, **omitting
`.modules = {sqlite}` from a snippet that uses SQLite (or similarly
omitting any other bundled module you actually use)**, rendering
`{{#tasks}}` at root after a join, **wrapping `{{#tasks}}` in a
section but leaving the parent's own fields (`{{name}}`, `{{id}}`)
bare at root** (you must open `{{#project}}` for ALL parent fields,
not just the joined children), dropping bare HTML/Mustache between
two `"..."` strings in a template, double-quoting SQL column names,
or putting `.databases` after a `};` that already closed `(config){...}`
— stop and fix it.
When in doubt about parent + child: copy the **canonical worked
snippet at the end of Rule 2** and rename. That snippet is the
correct shape for every "thing-with-children" pipeline, including
the C-syntax patterns.