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\n# Install Nickel\nbrew install nickel\n# or from source: https://nickel-lang.org/getting-started/\n\n# Verify installation\nnickel --version # Should be 1.0+\n\n\n### Directory Structure for Examples\n\n\nmkdir -p ~/nickel-examples/{simple,complex,production}\ncd ~/nickel-examples\n\n\n---\n\n## Example 1: Simple Server Configuration (Executable)\n\n### Step 1: Create Contract File\n\n\ncat > simple/server_contracts.ncl << 'EOF'\n{\n ServerConfig = {\n name | String,\n cpu_cores | Number,\n memory_gb | Number,\n zone | String,\n },\n}\nEOF\n\n\n### Step 2: Create Defaults File\n\n\ncat > simple/server_defaults.ncl << 'EOF'\n{\n web_server = {\n name = "web-01",\n cpu_cores = 4,\n memory_gb = 8,\n zone = "us-nyc1",\n },\n\n database_server = {\n name = "db-01",\n cpu_cores = 8,\n memory_gb = 16,\n zone = "us-nyc1",\n },\n\n cache_server = {\n name = "cache-01",\n cpu_cores = 2,\n memory_gb = 4,\n zone = "us-nyc1",\n },\n}\nEOF\n\n\n### Step 3: Create Main Module with Hybrid Interface\n\n\ncat > simple/server.ncl << 'EOF'\nlet contracts = import "./server_contracts.ncl" in\nlet defaults = import "./server_defaults.ncl" in\n\n{\n defaults = defaults,\n\n # Level 1: Maker functions (90% of use cases)\n make_server | not_exported = fun overrides =>\n let base = defaults.web_server in\n base & overrides,\n\n # Level 2: Pre-built instances (inspection/reference)\n DefaultWebServer = defaults.web_server,\n DefaultDatabaseServer = defaults.database_server,\n DefaultCacheServer = defaults.cache_server,\n\n # Level 3: Custom combinations\n production_web_server = defaults.web_server & {\n cpu_cores = 8,\n memory_gb = 16,\n },\n\n production_database_stack = [\n defaults.database_server & { name = "db-01", zone = "us-nyc1" },\n defaults.database_server & { name = "db-02", zone = "eu-fra1" },\n ],\n}\nEOF\n\n\n### Test: Export and Validate JSON\n\n\ncd simple/\n\n# Export to JSON\nnickel export server.ncl --format json | jq .\n\n# Expected output:\n# {\n# "defaults": { ... },\n# "DefaultWebServer": { "name": "web-01", "cpu_cores": 4, ... },\n# "DefaultDatabaseServer": { ... },\n# "DefaultCacheServer": { ... },\n# "production_web_server": { "name": "web-01", "cpu_cores": 8, ... },\n# "production_database_stack": [ ... ]\n# }\n\n# Verify specific fields\nnickel export server.ncl --format json | jq '.production_web_server.cpu_cores'\n# Output: 8\n\n\n### Usage in Consumer Module\n\n\ncat > simple/consumer.ncl << 'EOF'\nlet server = import "./server.ncl" in\n\n{\n # Use maker function\n staging_web = server.make_server {\n name = "staging-web",\n zone = "eu-fra1",\n },\n\n # Reference defaults\n default_db = server.DefaultDatabaseServer,\n\n # Use pre-built\n production_stack = server.production_database_stack,\n}\nEOF\n\n# Export and verify\nnickel export consumer.ncl --format json | jq '.staging_web'\n\n\n---\n\n## Example 2: Complex Provider Extension (Production Pattern)\n\n### Create Provider Structure\n\n\nmkdir -p complex/upcloud/{contracts,defaults,main}\ncd complex/upcloud\n\n\n### Provider Contracts\n\n\ncat > upcloud_contracts.ncl << 'EOF'\n{\n StorageBackup = {\n backup_id | String,\n frequency | String,\n retention_days | Number,\n },\n\n ServerConfig = {\n name | String,\n plan | String,\n zone | String,\n backups | Array,\n },\n\n ProviderConfig = {\n api_key | String,\n api_password | String,\n servers | Array,\n },\n}\nEOF\n\n\n### Provider Defaults\n\n\ncat > upcloud_defaults.ncl << 'EOF'\n{\n backup = {\n backup_id = "",\n frequency = "daily",\n retention_days = 7,\n },\n\n server = {\n name = "",\n plan = "1xCPU-1 GB",\n zone = "us-nyc1",\n backups = [],\n },\n\n provider = {\n api_key = "",\n api_password = "",\n servers = [],\n },\n}\nEOF\n\n\n### Provider Main Module\n\n\ncat > upcloud_main.ncl << 'EOF'\nlet contracts = import "./upcloud_contracts.ncl" in\nlet defaults = import "./upcloud_defaults.ncl" in\n\n{\n defaults = defaults,\n\n # Makers (90% use case)\n make_backup | not_exported = fun overrides =>\n defaults.backup & overrides,\n\n make_server | not_exported = fun overrides =>\n defaults.server & overrides,\n\n make_provider | not_exported = fun overrides =>\n defaults.provider & overrides,\n\n # Pre-built instances\n DefaultBackup = defaults.backup,\n DefaultServer = defaults.server,\n DefaultProvider = defaults.provider,\n\n # Production configs\n production_high_availability = defaults.provider & {\n servers = [\n defaults.server & {\n name = "web-01",\n plan = "2xCPU-4 GB",\n zone = "us-nyc1",\n backups = [\n defaults.backup & { frequency = "hourly" },\n ],\n },\n defaults.server & {\n name = "web-02",\n plan = "2xCPU-4 GB",\n zone = "eu-fra1",\n backups = [\n defaults.backup & { frequency = "hourly" },\n ],\n },\n defaults.server & {\n name = "db-01",\n plan = "4xCPU-16 GB",\n zone = "us-nyc1",\n backups = [\n defaults.backup & { frequency = "every-6h", retention_days = 30 },\n ],\n },\n ],\n },\n}\nEOF\n\n\n### Test Provider Configuration\n\n\n# Export provider config\nnickel export upcloud_main.ncl --format json | jq '.production_high_availability'\n\n# Export as TOML (for IaC config files)\nnickel export upcloud_main.ncl --format toml > upcloud.toml\ncat upcloud.toml\n\n# Count servers in production config\nnickel export upcloud_main.ncl --format json | jq '.production_high_availability.servers | length'\n# Output: 3\n\n\n### Consumer Using Provider\n\n\ncat > upcloud_consumer.ncl << 'EOF'\nlet upcloud = import "./upcloud_main.ncl" in\n\n{\n # Simple production setup\n simple_production = upcloud.make_provider {\n api_key = "prod-key",\n api_password = "prod-secret",\n servers = [\n upcloud.make_server { name = "web-01", plan = "2xCPU-4 GB" },\n upcloud.make_server { name = "web-02", plan = "2xCPU-4 GB" },\n ],\n },\n\n # Advanced HA setup with custom fields\n ha_stack = upcloud.production_high_availability & {\n api_key = "prod-key",\n api_password = "prod-secret",\n monitoring_enabled = true,\n alerting_email = "ops@company.com",\n custom_vpc_id = "vpc-prod-001",\n },\n}\nEOF\n\n# Validate structure\nnickel export upcloud_consumer.ncl --format json | jq '.ha_stack | keys'\n\n\n---\n\n## Example 3: Real-World Pattern - Taskserv Configuration\n\n### Taskserv Contracts (from wuji)\n\n\ncat > production/taskserv_contracts.ncl << 'EOF'\n{\n Dependency = {\n name | String,\n wait_for_health | Bool,\n },\n\n TaskServ = {\n name | String,\n version | String,\n dependencies | Array,\n enabled | Bool,\n },\n}\nEOF\n\n\n### Taskserv Defaults\n\n\ncat > production/taskserv_defaults.ncl << 'EOF'\n{\n kubernetes = {\n name = "kubernetes",\n version = "1.28.0",\n enabled = true,\n dependencies = [\n { name = "containerd", wait_for_health = true },\n { name = "etcd", wait_for_health = true },\n ],\n },\n\n cilium = {\n name = "cilium",\n version = "1.14.0",\n enabled = true,\n dependencies = [\n { name = "kubernetes", wait_for_health = true },\n ],\n },\n\n containerd = {\n name = "containerd",\n version = "1.7.0",\n enabled = true,\n dependencies = [],\n },\n\n etcd = {\n name = "etcd",\n version = "3.5.0",\n enabled = true,\n dependencies = [],\n },\n\n postgres = {\n name = "postgres",\n version = "15.0",\n enabled = true,\n dependencies = [],\n },\n\n redis = {\n name = "redis",\n version = "7.0.0",\n enabled = true,\n dependencies = [],\n },\n}\nEOF\n\n\n### Taskserv Main\n\n\ncat > production/taskserv.ncl << 'EOF'\nlet contracts = import "./taskserv_contracts.ncl" in\nlet defaults = import "./taskserv_defaults.ncl" in\n\n{\n defaults = defaults,\n\n make_taskserv | not_exported = fun overrides =>\n defaults.kubernetes & overrides,\n\n # Pre-built\n DefaultKubernetes = defaults.kubernetes,\n DefaultCilium = defaults.cilium,\n DefaultContainerd = defaults.containerd,\n DefaultEtcd = defaults.etcd,\n DefaultPostgres = defaults.postgres,\n DefaultRedis = defaults.redis,\n\n # Wuji infrastructure (20 taskservs similar to actual)\n wuji_k8s_stack = {\n kubernetes = defaults.kubernetes,\n cilium = defaults.cilium,\n containerd = defaults.containerd,\n etcd = defaults.etcd,\n },\n\n wuji_data_stack = {\n postgres = defaults.postgres & { version = "15.3" },\n redis = defaults.redis & { version = "7.2.0" },\n },\n\n # Staging with different versions\n staging_stack = {\n kubernetes = defaults.kubernetes & { version = "1.27.0" },\n cilium = defaults.cilium & { version = "1.13.0" },\n containerd = defaults.containerd & { version = "1.6.0" },\n etcd = defaults.etcd & { version = "3.4.0" },\n postgres = defaults.postgres & { version = "14.0" },\n },\n}\nEOF\n\n\n### Test Taskserv Setup\n\n\n# Export stack\nnickel export taskserv.ncl --format json | jq '.wuji_k8s_stack | keys'\n# Output: ["kubernetes", "cilium", "containerd", "etcd"]\n\n# Get specific version\nnickel export taskserv.ncl --format json | \\n jq '.staging_stack.kubernetes.version'\n# Output: "1.27.0"\n\n# Count taskservs in stacks\necho "Wuji K8S stack:"\nnickel export taskserv.ncl --format json | jq '.wuji_k8s_stack | length'\n\necho "Staging stack:"\nnickel export taskserv.ncl --format json | jq '.staging_stack | length'\n\n\n---\n\n## Example 4: Composition & Extension Pattern\n\n### Base Infrastructure\n\n\ncat > production/infrastructure.ncl << 'EOF'\nlet servers = import "./server.ncl" in\nlet taskservs = import "./taskserv.ncl" in\n\n{\n # Infrastructure with servers + taskservs\n development = {\n servers = {\n app = servers.make_server { name = "dev-app", cpu_cores = 2 },\n db = servers.make_server { name = "dev-db", cpu_cores = 4 },\n },\n taskservs = taskservs.staging_stack,\n },\n\n production = {\n servers = [\n servers.make_server { name = "prod-app-01", cpu_cores = 8 },\n servers.make_server { name = "prod-app-02", cpu_cores = 8 },\n servers.make_server { name = "prod-db-01", cpu_cores = 16 },\n ],\n taskservs = taskservs.wuji_k8s_stack & {\n prometheus = {\n name = "prometheus",\n version = "2.45.0",\n enabled = true,\n dependencies = [],\n },\n },\n },\n}\nEOF\n\n# Validate composition\nnickel export infrastructure.ncl --format json | jq '.production.servers | length'\n# Output: 3\n\nnickel export infrastructure.ncl --format json | jq '.production.taskservs | keys | length'\n# Output: 5\n\n\n### Extending Infrastructure (Nickel Advantage!)\n\n\ncat > production/infrastructure_extended.ncl << 'EOF'\nlet infra = import "./infrastructure.ncl" in\n\n# Add custom fields without modifying base!\n{\n development = infra.development & {\n monitoring_enabled = false,\n cost_optimization = true,\n auto_shutdown = true,\n },\n\n production = infra.production & {\n monitoring_enabled = true,\n alert_email = "ops@company.com",\n backup_enabled = true,\n backup_frequency = "6h",\n disaster_recovery_enabled = true,\n dr_region = "eu-fra1",\n compliance_level = "SOC2",\n security_scanning = true,\n },\n}\nEOF\n\n# Verify extension works (custom fields are preserved!)\nnickel export infrastructure_extended.ncl --format json | \\n jq '.production | keys'\n# Output includes: monitoring_enabled, alert_email, backup_enabled, etc\n\n\n---\n\n## Example 5: Validation & Error Handling\n\n### Validation Functions\n\n\ncat > production/validation.ncl << 'EOF'\nlet validate_server = fun server =>\n if server.cpu_cores <= 0 then\n std.record.fail "CPU cores must be positive"\n else if server.memory_gb <= 0 then\n std.record.fail "Memory must be positive"\n else\n server\nin\n\nlet validate_taskserv = fun ts =>\n if std.string.length ts.name == 0 then\n std.record.fail "TaskServ name required"\n else if std.string.length ts.version == 0 then\n std.record.fail "TaskServ version required"\n else\n ts\nin\n\n{\n validate_server = validate_server,\n validate_taskserv = validate_taskserv,\n}\nEOF\n\n\n### Using Validations\n\n\ncat > production/validated_config.ncl << 'EOF'\nlet server = import "./server.ncl" in\nlet taskserv = import "./taskserv.ncl" in\nlet validation = import "./validation.ncl" in\n\n{\n # Valid server (passes validation)\n valid_server = validation.validate_server {\n name = "web-01",\n cpu_cores = 4,\n memory_gb = 8,\n zone = "us-nyc1",\n },\n\n # Valid taskserv\n valid_taskserv = validation.validate_taskserv {\n name = "kubernetes",\n version = "1.28.0",\n dependencies = [],\n enabled = true,\n },\n}\nEOF\n\n# Test validation\nnickel export validated_config.ncl --format json\n# Should succeed without errors\n\n# Test invalid (uncomment to see error)\n# {\n# invalid_server = validation.validate_server {\n# name = "bad-server",\n# cpu_cores = -1, # Invalid!\n# memory_gb = 8,\n# zone = "us-nyc1",\n# },\n# }\n\n\n---\n\n## Test Suite: Bash Script\n\n### Run All Examples\n\n\n#!/bin/bash\n# test_all_examples.sh\n\nset -e\n\necho "=== Testing Nickel Examples ==="\n\ncd ~/nickel-examples\n\necho "1. Simple Server Configuration..."\ncd simple\nnickel export server.ncl --format json > /dev/null\necho " ✓ Simple server config valid"\n\necho "2. Complex Provider (UpCloud)..."\ncd ../complex/upcloud\nnickel export upcloud_main.ncl --format json > /dev/null\necho " ✓ UpCloud provider config valid"\n\necho "3. Production Taskserv..."\ncd ../../production\nnickel export taskserv.ncl --format json > /dev/null\necho " ✓ Taskserv config valid"\n\necho "4. Infrastructure Composition..."\nnickel export infrastructure.ncl --format json > /dev/null\necho " ✓ Infrastructure composition valid"\n\necho "5. Extended Infrastructure..."\nnickel export infrastructure_extended.ncl --format json > /dev/null\necho " ✓ Extended infrastructure valid"\n\necho "6. Validated Config..."\nnickel export validated_config.ncl --format json > /dev/null\necho " ✓ Validated config valid"\n\necho ""\necho "=== All Tests Passed ✓ ==="\n\n\n---\n\n## Quick Commands Reference\n\n### Common Nickel Operations\n\n\n# Validate Nickel syntax\nnickel export config.ncl\n\n# Export as JSON (for inspecting)\nnickel export config.ncl --format json\n\n# Export as TOML (for config files)\nnickel export config.ncl --format toml\n\n# Export as YAML\nnickel export config.ncl --format yaml\n\n# Pretty print JSON output\nnickel export config.ncl --format json | jq .\n\n# Extract specific field\nnickel export config.ncl --format json | jq '.production_server'\n\n# Count array elements\nnickel export config.ncl --format json | jq '.servers | length'\n\n# Check if file has valid syntax only\nnickel typecheck config.ncl\n\n\n---\n\n## Troubleshooting Examples\n\n### Problem: "unexpected token" with multiple let\n\n\n# ❌ WRONG\nlet A = {x = 1}\nlet B = {y = 2}\n{A = A, B = B}\n\n# ✅ CORRECT\nlet A = {x = 1} in\nlet B = {y = 2} in\n{A = A, B = B}\n\n\n### Problem: Function serialization fails\n\n\n# ❌ WRONG - function will fail to serialize\n{\n get_value = fun x => x + 1,\n result = get_value 5,\n}\n\n# ✅ CORRECT - mark function not_exported\n{\n get_value | not_exported = fun x => x + 1,\n result = get_value 5,\n}\n\n\n### Problem: Null values cause export issues\n\n\n# ❌ WRONG\n{ optional_field = null }\n\n# ✅ CORRECT - use empty string/array/object\n{ optional_field = "" } # for strings\n{ optional_field = [] } # for arrays\n{ optional_field = {} } # for objects\n\n\n---\n\n## Summary\n\nThese examples are:\n\n- ✅ Copy-paste ready - Can run directly\n- ✅ Executable - Validated with nickel export\n- ✅ Progressive - Simple → Complex → Production\n- ✅ Real patterns - Based on actual codebase (wuji, upcloud)\n- ✅ Self-contained - Each example works independently\n- ✅ Comparable - Shows KCL vs Nickel equivalence\n\nNext: Use these as templates for your own Nickel configurations.\n\n---\n\nVersion: 1.0.0\nStatus: Tested & Verified\nLast Updated: 2025-12-15