Core Concepts

Application

The Application class is the composition root. It manages providers, modules, configuration, and lifecycle.

from lexigram import Application, LexigramConfig

def create_app() -> Application:
    config = LexigramConfig.from_yaml()
    app = Application(name="my-app", config=config)
    # Wire services here...
    return app

Key methods on Application:

Method	Purpose
`add_provider(provider)`	Register a `Provider` instance
`add_module(module)`	Register a `@module` class or `DynamicModule`
`discover_providers(*packages)`	Scan packages for `Provider` subclasses and `@injectable` classes
`start()`	Boot all providers (register → freeze → boot)
`stop()`	Shutdown in reverse order
`Application.boot(...)`	Context manager — `start()`, yield, `stop()`

# Context manager form
async with Application.boot(
    name="my-app",
    providers=[AppProvider(), WebProvider()],
    config=config,
) as app:
    # app is started and ready
    pass

Providers

Providers register services in the DI container and manage their lifecycle. Every provider follows a two-phase pattern:

from lexigram.di.provider import Provider
from lexigram.contracts.core import ProviderPriority
from lexigram.contracts.core.di import (
    ContainerRegistrarProtocol,
    ContainerResolverProtocol,
)


class AppProvider(Provider):
    name = "app"
    priority = ProviderPriority.DOMAIN

    async def register(self, container: ContainerRegistrarProtocol) -> None:
        """Phase 1: Declare bindings. No resolving allowed."""
        from my_app.domain.services import UserService

        container.singleton(UserService, UserService)

    async def boot(self, container: ContainerResolverProtocol) -> None:
        """Phase 2: Initialize resources. Resolving is now safe."""
        service = await container.resolve(UserService)
        await service.warmup_cache()

Provider Priorities

Providers boot in ascending order. Lower values run first:

Priority	Value	Purpose	Example
`CRITICAL`	0	Absolutely foundational	Config, diagnostics
`INFRASTRUCTURE`	10	Low-level plumbing	Database, cache, message brokers
`SECURITY`	20	Auth infrastructure	Auth, encryption
`NORMAL`	30	Everyday services (default)	Generic services
`APPLICATION`	40	Application-level tools	CLI, admin utilities
`DOMAIN`	50	Business logic	Your domain providers
`PRESENTATION`	80	Entry points	`WebProvider`
`COMMS`	90	Outbound communication	Email, SMS, webhooks
`LOW`	100	Optional, boot last	Plugins, analytics

Config Auto-Injection

Providers can declare config_key and config_model to automatically receive their typed configuration section from application.yaml:

class CacheProvider(Provider):
    name = "cache"
    config_key = "cache"          # reads the "cache:" section
    config_model = CacheConfig    # coerces it into CacheConfig

    async def register(self, container: ContainerRegistrarProtocol) -> None:
        # self.config is now a typed CacheConfig — injected by the orchestrator
        cfg = self.config or CacheConfig()
        container.singleton(CacheBackend, RedisCacheBackend(cfg))

The ProviderOrchestrator calls LexigramConfig.get_section(config_key, config_model) before register() and assigns the result to provider.config.

Provider Lifecycle Hooks

Hook	Phase	When Called
`register(container)`	Registration	Container open for bindings
`boot(container)`	Boot	Container frozen, resolution allowed
`shutdown()`	Shutdown	Application stopping
`on_error(error, phase)`	Error	When `boot()` or `shutdown()` raises
`health_check(timeout)`	Health	Aggregated by `Application.health_check()`

Dependency Injection

Lexigram uses constructor injection — declare dependencies as type hints, the container resolves them automatically:

class OrderService:
    def __init__(
        self,
        repo: OrderRepositoryProtocol,    # ← resolved from container
        event_bus: EventBusProtocol,       # ← resolved from container
    ) -> None:
        self.repo = repo
        self.event_bus = event_bus

Container API

The container uses a key → value binding pattern. The first argument is the type you resolve by, the second is what you get back:

from lexigram import Container

container = Container()

# Registration — key: type to resolve, value: what to return
container.singleton(PaymentGateway, StripeGateway(api_key))   # protocol → instance
container.singleton(UserService, UserService())                # class → pre-built instance
container.singleton(CacheBackend, factory=create_redis)        # lazy factory
container.scoped(DbSession, SqlAlchemySession)                 # one per scope (class as factory)
container.transient(RequestContext, RequestContext)             # new instance each resolve

# Resolution
service = await container.resolve(PaymentGateway)     # returns the StripeGateway instance
optional = await container.resolve_optional(EventBus) # None if not registered
all_impls = await container.resolve_all(BaseHandler)  # all subtypes
sync_val = container.resolve_sync(UserService)        # sync (instantiated singletons only)

# Scoping
async with container.scope() as scoped:
    session = await scoped.resolve(DbSession)          # scoped to this block

# Lifecycle
container.freeze()                      # no more registrations allowed
container.override(Service, fake)       # testing_mode=True only
await container.dispose()               # cleanup all singletons

DI Decorators

Decorator	Scope	Import From
`@singleton`	One instance for the app	`lexigram`
`@injectable`	Transient by default	`lexigram`
`@scoped`	One instance per request/scope	`lexigram`
`@transient`	New instance each time	`lexigram`
`@inject`	Enable DI on async functions	`lexigram`

from lexigram import singleton, injectable, inject

@singleton
class ConfigService:
    def __init__(self) -> None:
        self.settings = load_settings()

@injectable  # transient by default
class UserService:
    def __init__(self, config: ConfigService) -> None:
        self.config = config

@inject
async def handle_request(user_svc: UserService) -> None:
    # user_svc resolved via container.call() or Invoker.invoke()
    ...

Result Type

Lexigram uses Result[T, E] for operations that can fail — no exceptions for expected errors.

from lexigram.result import Result, Ok, Err

async def find_user(self, user_id: str) -> Result[User, DomainError]:
    user = await self.repo.get(user_id)
    if not user:
        return Err(UserNotFound(user_id))
    return Ok(user)

Working With Results

result = await service.find_user("user-42")

# Check + unwrap
if result.is_ok():
    user = result.unwrap()
if result.is_err():
    error = result.unwrap_err()

# Safe access
user = result.unwrap_or(default_user)
user = result.unwrap_or_else(lambda e: create_fallback(e))

# Pattern matching
message = result.match(
    ok=lambda user: user.name,
    err=lambda error: str(error),
)

# Chaining (sync)
name = result.map_sync(lambda u: u.name).unwrap_or("anonymous")

# Chaining (async)
profile = await result.map(fetch_profile).and_then(enrich_profile)

# Filtering
valid = result.filter(lambda u: u.is_active, InactiveUserError())

# Side effects without transformation
result.inspect(lambda u: logger.info("found", user=u.id))
result.inspect_err(lambda e: logger.warning("failed", error=str(e)))

# Nesting
nested: Result[Result[str, E], E] = Ok(Ok("hello"))
flat = nested.flatten()  # → Ok("hello")

# Bridge from exceptions
try:
    data = json.loads(raw)
except ValueError as e:
    return Result.from_exception(e)

Utilities

from lexigram.result import (
    as_result,           # decorator: wraps async fn exceptions into Err
    as_result_sync,      # decorator: wraps sync fn exceptions into Err
    collect,             # list[Result[T, E]] → Result[list[T], E]
    partition,           # list[Result[T, E]] → (list[T], list[E])
    try_catch,           # async: try/catch → Result
    try_catch_sync,      # sync: try/catch → Result
    ResultPipeline,      # chainable pipeline builder
)

Modules

For larger projects (Pattern 3), modules add encapsulation boundaries over providers. Services inside a module are private by default — only explicitly exported types are visible to importers.

from lexigram.di.module import module

@module(
    imports=[AuthModule],                  # can use AuthServiceProtocol
    providers=[BillingProvider],
    exports=[BillingServiceProtocol],      # only this is visible outside
)
class BillingModule:
    """Billing — depends on auth for user verification."""

Dynamic Modules

For infrastructure that needs runtime configuration, override configure() on the Module base class:

from lexigram.di.module import module, Module, DynamicModule

@module()
class DatabaseModule(Module):

    @classmethod
    def configure(cls, url: str) -> DynamicModule:
        return DynamicModule(
            module=cls,
            providers=[DatabaseProvider(url=url)],
            exports=[DatabaseSession, TransactionManager],
            is_global=True,  # visible to all modules
        )

Usage in your app:

app.add_module(DatabaseModule.configure("postgresql://localhost/mydb"))

The Module base class provides three factory methods:

Method	Purpose
`configure(args, *kwargs)`	Global configuration — called once at the app root
`scope(*providers)`	Register additional providers in a per-feature scope
`stub(config)`	Return a test-mode module with in-memory/noop backends

Global Modules

A @global_module’s exports are visible to all modules without explicit import:

from lexigram.di.module import global_module, Module

@global_module
class LoggingModule(Module):
    providers = [LoggingProvider]
    exports = [LoggerProtocol]

Why Modules?

Without Modules (Pattern 2)	With Modules (Pattern 3)
Every service is globally visible	Services are private by default
Any class can depend on any other	Only exported protocols are accessible
No encapsulation boundaries	`ModuleCompiler` validates the import/export graph at boot

Application Lifecycle

┌─────────────────────────────────────────┐
│        Application(name, config)         │  AppState.CREATED
└─────────────────┬───────────────────────┘
                  │ app.start()
                  ▼
┌─────────────────────────────────────────┐
│   ModuleCompiler.compile() (if modules)  │  Validates import/export graph
└─────────────────┬───────────────────────┘
                  │
                  ▼
┌─────────────────────────────────────────┐
│   Provider.register() — all providers    │  Bind services (no resolving)
└─────────────────┬───────────────────────┘
                  │
                  ▼
┌─────────────────────────────────────────┐
│         Container.freeze()               │  No more registrations
└─────────────────┬───────────────────────┘
                  │
                  ▼
┌─────────────────────────────────────────┐
│    Provider.boot() — all providers       │  Initialize resources (resolving OK)
└─────────────────┬───────────────────────┘
                  │                            AppState.RUNNING
                  ▼
┌─────────────────────────────────────────┐
│         Application running              │  Serving traffic
└─────────────────┬───────────────────────┘
                  │ app.stop()
                  ▼
┌─────────────────────────────────────────┐
│  Provider.shutdown() — reverse order     │  Cleanup resources
└─────────────────┬───────────────────────┘
                  │
                  ▼
┌─────────────────────────────────────────┐
│       Container.dispose()                │  AppState.STOPPED
└─────────────────────────────────────────┘

Next Steps

Configuration — YAML config, environment profiles, and auto-injection
lexigram-web — Controllers, routing, and middleware