Services¶

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Services declare custom business logic in DSL with implementation in Python or TypeScript stubs. DAZZLE separates concerns into three layers: DSL (declarative), Kernel (runtime), and Stubs (custom code). This page covers domain services, stubs, action purity, and component roles.

Domain Service¶

Custom business logic declaration in DSL with implementation in Python/TypeScript stubs. Part of the Anti-Turing extensibility model.

Syntax¶

service <name> "<Title>":
  kind: <domain_logic|validation|integration|workflow>
  input:
    <field_name>: <type> [required]
    ...
  output:
    <field_name>: <type>
    ...
  guarantees:
    - "<contract guarantee>"
  stub: <python|typescript>

Example¶

service calculate_vat "Calculate VAT":
  kind: domain_logic
  input:
    invoice_id: uuid required
    country_code: str(2)
  output:
    vat_amount: decimal(10,2)
    breakdown: json
  guarantees:
    - "Must not mutate the invoice record"
    - "Must raise domain error if config incomplete"
  stub: python

Related: Stub, Three Layer Architecture

Stub¶

Turing-complete implementation of a domain service. Stubs are auto-generated from DSL with typed function signatures.

Example¶

# stubs/calculate_vat.py (auto-generated header)
# === AUTO-GENERATED HEADER - DO NOT MODIFY ===
# Service ID: calculate_vat
# Kind: domain_logic
# Input: invoice_id (uuid required), country_code (str(2) optional)
# Output: vat_amount (decimal), breakdown (json)
# ============================================

from typing import TypedDict

class CalculateVatResult(TypedDict):
    vat_amount: float
    breakdown: dict

def calculate_vat(invoice_id: str, country_code: str | None = None) -> CalculateVatResult:
    # Your implementation here
    invoice = get_invoice(invoice_id)
    vat_rate = get_vat_rate(country_code or invoice.country)
    return {
        "vat_amount": invoice.total * vat_rate,
        "breakdown": {"rate": vat_rate, "country": country_code}
    }

Action Purity¶

Classification of actions as pure (no side effects) or impure (has side effects like fetch, navigate, etc.).

Syntax¶

actions:
  toggleFilter: pure    # Only affects local state
  saveTask: impure      # Has side effect (API call)

Related: Component Role

Component Role¶

Classification of components as presentational (no state/impure actions) or container (has state or impure actions).

Related: Action Purity

Three Layer Architecture¶

DAZZLE's separation of concerns: DSL (declarative) → Kernel (runtime) → Stubs (custom code). The DSL is Anti-Turing (no arbitrary computation) while stubs allow full programming.

Related: Domain Service, Stub