Nickel

Nickel Configuration Language

Gradual typing + contracts for configuration that composes correctly.

Dynamic Sufficiency

A Nickel config is dynamically sufficient when:

1. Structural: Contract coverage is complete (all fields typed)
2. Computational: Same outputs for all valid inputs
3. Semantic: Olog types preserved through transformations

# Sufficiency levels (from dynamic_sufficiency.jl)
let SufficiencyLevel = [|
  'NOT_SUFFICIENT,           # Different behavior
  'WEAKLY_SUFFICIENT,        # Same structure, different labels  
  'COMPUTATIONALLY_SUFFICIENT,  # Same outputs
  'SEMANTICALLY_SUFFICIENT      # Same olog meaning
|]

Core Contracts

Import from workspace:

let contracts = import ".topos/nickel/contracts/transformation-contracts.ncl"

Available contracts:

• TransformationPattern - rename/refactor operations
• TransformationStrategy - checkpoint + rollback + validation
• BalancedTernarySelector - GF(3) strategy selection (seed 1069)
• ValidationResult - gate pass/fail with exit codes

Gradual Typing Pattern

# Untyped (dynamic) - simple configs
{ name = "example", count = 42 }

# Typed block - contract enforcement
let typed_config : { name: String, count: Number } = 
  { name = "example", count = 42 }

# Contract annotation - runtime validation
let validated = config | TransformationStrategy

Idempotent Contracts

# Good: applying twice yields same result
let Positive = std.contract.from_predicate (fun x => x > 0)
5 | Positive | Positive  # ✓ idempotent

# Key property for dynamic sufficiency:
# ∀c: Contract, ∀x: (x | c) | c ≡ x | c

Workspace Integration

CLI Usage

# Evaluate config
nickel eval config.ncl

# Type-check without eval
nickel typecheck config.ncl

# Export to JSON
nickel export config.ncl --format json

# REPL
nickel repl

GF(3) Integration

Trit: 0 (ERGODIC - synthesis/validation)
Home: Prof
Poly Op: ⊗
Color: #FFFF00

Triadic pairing:

• dune-analytics (+1) - expanding/querying
• nickel (0) - contract validation
• sicp (-1) - foundational evaluation

Dynamic Sufficiency Verification

# Verify sufficiency between two configs
let verify_sufficiency = fun cfg1 cfg2 =>
  let fields1 = std.record.fields cfg1 in
  let fields2 = std.record.fields cfg2 in
  if std.array.all (fun f => std.array.elem f fields2) fields1
  then 'COMPUTATIONALLY_SUFFICIENT
  else 'NOT_SUFFICIENT

SDF Interleaving

This skill connects to Software Design for Flexibility (Hanson & Sussman, 2021):

Primary Chapter: 8. Degeneracy

Concepts: redundancy, fallback, multiple strategies, robustness

GF(3) Balanced Triad

nickel (−) + SDF.Ch8 (−) + [balancer] (−) = 0

Skill Trit: -1 (MINUS - verification)

Secondary Chapters

• Ch5: Evaluation
• Ch1: Flexibility through Abstraction
• Ch4: Pattern Matching
• Ch2: Domain-Specific Languages

Connection Pattern

Degeneracy provides fallbacks. This skill offers redundant strategies.