Language

Modules (use / export)

Split code across files. export makes a task/type/let/enum/routes public; anything else stays private. A module is a map of its exports, imported under an alias.

The module — mathlib.syn:

export task square(n)
    give n * n

export let VERSION be "1.0"

task private_helper()        -- no `export` → not visible to importers
    give 42

The entry that imports it:

-- Doc example: modules (use / export). Imports ./mathlib.syn under the alias `math`.
intent: "doc example: modules"
use "./mathlib.syn" as math

print("math.square(5) = " + text(math.square(5)) + ",  VERSION " + math.VERSION)

test "import an exported task and let (private_helper is NOT visible)"
    assert_eq(math.square(5), 25)
    assert_eq(math.VERSION, "1.0")

Rules§

• use "./path.syn" as alias — paths are relative to the importing file; .syn only, no URLs/FFI, and traversal (../) is blocked.
• Cross-file calls need the alias prefix: math.square(5), math.VERSION.
• Imports are cached (loaded once), transitive, and cycle-checked.
• A module must not have a top-level require or serve — those belong in the entry file. A per-task require inside a module task is fine.
• synsema check entry.syn resolves and parses the whole import graph (broken paths, cycles, forbidden serve/require in modules all fail the check).

export routes — route groups a serve can mount§

A big site doesn't have to be one big serve block. A module exports a routes group; the entry mounts it (bodies can call the module's private helpers by simple name):

-- shop.syn
task fmt(n)                        -- private
    give "$" + text(n)

export routes shop
    route "GET /shop"
        give html("<h1>" + fmt(99) + "</h1>")
    route "POST /shop/buy"
        expect body {item: text}
        give created(json of request)

-- app.syn
use "./shop.syn" as shop
serve on 8080
    mount shop.shop                -- or: mount shop.shop at "/store"

Groups accept route entries with their own rate_limit and timeout (engine v0.6.19+: a mounted route gets its own rate zone, and a mount prefix is another zone — before v0.6.19 both were refused inside a group); stream and socket routes still belong in the serve block, and synsema check says so with the same message serve would give at start. A mounted requires auth still demands auth with on the serve block, validated when the serve is built. See HTTP server and Build a website.