Language Conversion Guide

Comprehensive patterns and strategies for converting code between programming languages.

Quick Navigation

Resource	Purpose
FORMS.md	Templates, checklists, decision trees
tables/quick-reference.md	Condensed lookup tables

Examples

File	Content
examples/idiom-translation.md	Null handling, collections, pattern matching
examples/error-handling.md	Exception→Result, error hierarchies
examples/concurrency.md	Promise/Future, parallel execution
examples/metaprogramming.md	Decorators, macros, DI patterns
examples/serialization.md	JSON, validation, polymorphic types

Reference Guides

File	Content
reference/difficulty-matrix.md	Conversion difficulty ratings
reference/type-system-mapping.md	Primitives, composites, generics
reference/error-handling.md	Error models, let-it-crash
reference/concurrency.md	Async models, channels, goroutines
reference/dev-workflow-repl.md	9th pillar, REPL patterns
reference/memory-ownership.md	GC→ownership, borrowing
reference/evaluation-strategy.md	Lazy vs eager patterns
reference/metaprogramming.md	Macros, reflection, code gen
reference/type-system-translation.md	Static↔dynamic, inference
reference/paradigm-translation.md	OOP→FP, FP→FP
reference/serialization.md	Library mapping, attributes
reference/typescript-patterns.md	Type guards, mapped types
reference/hkt-type-classes.md	HKTs, Functor, Monad
reference/async-patterns.md	Cancellation, streams
reference/dependency-management.md	Package ecosystems
reference/performance.md	Pitfalls, benchmarking

Gotchas

File	Content
reference/gotchas/by-family.md	OOP→FP, Dynamic→Static, GC→Ownership
reference/gotchas/by-language.md	Python→Rust, TypeScript→Rust, etc.

---

When to Use This Skill

• Converting code from one language to another
• Planning a language migration
• Understanding conversion challenges between languages
• Looking up type mappings or idiom translations
• Referencing error handling, concurrency, or async patterns across languages
• Learning about gotchas when converting between specific language families

This Skill Does NOT Cover

• Creating new conversion skills (see meta-convert-dev)
• Language tutorials (see lang-*-dev skills)
• Runtime interop/FFI (see language-specific interop skills)

Related Skills

• meta-convert-dev - For creating new convert-X-Y skills
• convert-* skills - Language-pair specific conversion skills

---

Core Conversion Methodology

The APTV Workflow

Every conversion follows: Analyze → Plan → Transform → Validate

┌─────────────────────────────────────────────────────────────┐
│                    CONVERSION WORKFLOW                       │
├─────────────────────────────────────────────────────────────┤
│  1. ANALYZE    │  Understand source code structure          │
│                │  • Parse and identify components            │
│                │  • Map dependencies                         │
│                │  • Identify language-specific patterns      │
├─────────────────────────────────────────────────────────────┤
│  2. PLAN       │  Design the target architecture            │
│                │  • Create type mapping table                │
│                │  • Identify idiom translations              │
│                │  • Plan module/package structure            │
├─────────────────────────────────────────────────────────────┤
│  3. TRANSFORM  │  Convert code systematically               │
│                │  • Types and interfaces first               │
│                │  • Core logic second                        │
│                │  • Adopt target idioms (don't transliterate)│
├─────────────────────────────────────────────────────────────┤
│  4. VALIDATE   │  Verify functional equivalence             │
│                │  • Run original tests against new code      │
│                │  • Property-based testing for edge cases    │
│                │  • Performance comparison if relevant       │
└─────────────────────────────────────────────────────────────┘

See also: FORMS.md for APTV phase checklists

Analyze Phase

Before writing any target code:

1. Parse the source - Understand structure, not just syntax
2. Identify components:
   • Types/interfaces/classes
   • Functions/methods
   • Module boundaries
   • External dependencies
3. Note language-specific features:
   • Generics usage
   • Error handling patterns
   • Async patterns
   • Memory management approach

Plan Phase

Create explicit mappings before transforming. Use the templates in FORMS.md:

## Type Mapping Table

| Source (TypeScript) | Target (Rust)      | Notes             |
| ------------------- | ------------------ | ----------------- |
| `string`            | `String` / `&str`  | Owned vs borrowed |
| `number`            | `i32` / `f64`      | Specify precision |
| `T[]`               | `Vec<T>`           | Owned collection  |
| `T \| null`         | `Option<T>`        | Nullable handling |
| `Promise<T>`        | `Future<Output=T>` | Async handling    |

See also: reference/type-system-mapping.md for complete mappings

Transform Phase

Golden Rule: Adopt target idioms, don't write "Source code in Target syntax"

// Source: TypeScript
function findUser(id: string): User | null {
  const user = users.find((u) => u.id === id);
  return user || null;
}

// BAD: Transliterated (TypeScript in Rust clothing)
fn find_user(id: String) -> Option<User> {
    let user = users.iter().find(|u| u.id == id);
    match user {
        Some(u) => Some(u.clone()),
        None => None,
    }
}

// GOOD: Idiomatic Rust
fn find_user(id: &str) -> Option<&User> {
    users.iter().find(|u| u.id == id)
}

See also: examples/idiom-translation.md for more patterns

Validate Phase

1. Functional equivalence: Same inputs → same outputs
2. Edge case coverage: Property-based tests
3. Error behavior: Same error conditions trigger appropriately
4. Performance baseline: Comparable or better performance

See also: FORMS.md for testing strategy checklist

---

The 8 Pillars of Conversion

Every comprehensive conversion addresses these domains:

Pillar	What to Convert	Reference
1. Module System	Imports, exports, packages	reference/type-system-mapping.md
2. Error Handling	Exceptions, Results, panics	reference/error-handling.md
3. Concurrency	Async, threads, channels	reference/concurrency.md
4. Metaprogramming	Decorators, macros, reflection	reference/metaprogramming.md
5. Zero/Default Values	Nullability, defaults	reference/type-system-mapping.md
6. Serialization	JSON, validation, schemas	reference/serialization.md
7. Build System	Package managers, dependencies	reference/dependency-management.md
8. Testing	Test frameworks, assertions	FORMS.md

The 9th Pillar: Dev Workflow

For REPL-centric languages (Clojure, Elixir, Haskell), add:

Source	Target	Consideration
REPL-centric	Compiled	Document workflow changes
Hot reload	Recompile	Faster incremental builds
Live inspection	Debugging	Logger, debugger setup

See also: reference/dev-workflow-repl.md

---

Quick Reference Tables

Type System Comparison

Language	Typing	Null Safety	Generics
TypeScript	Static	Optional (strict)	Full
Python	Dynamic	None (runtime)	Type hints
Rust	Static	Enforced (Option)	Full
Go	Static	Nil pointers	1.18+
Elixir	Dynamic	nil atoms	None
Haskell	Static (HM)	Enforced (Maybe)	Full + HKT

See also: tables/quick-reference.md for complete tables

Error Model Comparison

Language	Model	Propagation
TypeScript	Exceptions	throw / try-catch
Python	Exceptions	raise / try-except
Rust	Result type	? operator
Go	Error returns	if err != nil
Elixir	Pattern match	{:ok, _} / {:error, _}
Haskell	Either/Maybe	Monadic bind

See also: reference/error-handling.md

Concurrency Model Comparison

Language	Model	Primitives
TypeScript	Event loop	Promises, async/await
Python	Event loop	asyncio, await
Rust	Futures	tokio, async/await
Go	CSP	Goroutines, channels
Elixir	Actors	Processes, GenServer
Erlang	Actors	Processes, mailboxes

See also: reference/concurrency.md

---

Common Conversion Patterns

Null Handling

Source	Target Rust	Pattern
x ?? default	x.unwrap_or(default)	Default value
x?.prop	x.map(|v| v.prop)	Optional chaining
if (x != null)	if let Some(v) = x	Null check

See also: examples/idiom-translation.md

Error Propagation

Source	Target	Pattern
throw new Error(msg)	return Err(Error::new(msg))	Throw → Result
try { } catch { }	match result { Ok(_) => ..., Err(_) => ... }	Try/catch → match
Rethrow	? operator	Propagate error

See also: examples/error-handling.md

Collection Operations

Source (JS/TS)	Target (Rust)	Notes
.map(f)	.iter().map(f)	Lazy in Rust
.filter(f)	.iter().filter(f)	Lazy in Rust
.reduce(f, init)	.iter().fold(init, f)	Different arg order
.find(f)	.iter().find(f)	Returns Option

See also: tables/quick-reference.md

---

Decision Trees

When to Clone vs Borrow

Is the data needed after the function returns?
├─ NO → Borrow (&T)
└─ YES → Does caller need to keep using it?
         ├─ NO → Move (T)
         └─ YES → Clone (.clone())

See also: FORMS.md for complete decision trees

GC → Ownership Strategy

Is this data shared across components?
├─ YES → Consider Arc<T> or Rc<T>
└─ NO → Single owner, use moves

Is this data mutated by multiple parts?
├─ YES → Arc<Mutex<T>> or channels
└─ NO → Immutable borrows (&T)

See also: reference/memory-ownership.md

---

Common Pitfalls

Pitfall	Wrong	Right
Transliteration	Write TypeScript in Rust syntax	Write idiomatic Rust
Ignoring idioms	Port class hierarchies to Rust	Use enums and traits
1:1 mapping	Every function maps exactly	Restructure as needed
Preserve inefficiency	Port inefficient algorithms	Optimize for target
Ignore conventions	camelCase in Python	snake_case (Python)

See also: reference/gotchas/by-family.md

---

Testing Conversions

Testing Pyramid

         ┌───────────────┐
         │  Integration  │  Same API behavior
         └───────────────┘
    ┌─────────────────────────┐
    │    Property-Based       │  Invariants hold
    └─────────────────────────┘
 ┌───────────────────────────────────┐
 │           Unit Tests              │  Logic matches
 └───────────────────────────────────┘
┌─────────────────────────────────────────┐
│        Input/Output Comparison          │  Golden tests
└─────────────────────────────────────────┘

Golden Testing

1. Generate test cases from original implementation
2. Save as JSON fixtures
3. Run converted code against same inputs
4. Compare outputs

See also: FORMS.md for testing checklist

---

Language-Specific Quick Links

Converting FROM

Source	Key Gotchas	Reference
Python	Duck typing, None everywhere	reference/gotchas/by-language.md
TypeScript	Optional properties, any	reference/typescript-patterns.md
Go	Zero values, nil	reference/gotchas/by-language.md
Java	Null, checked exceptions	reference/gotchas/by-language.md
Haskell	HKTs, laziness	reference/hkt-type-classes.md
Elixir	Pattern matching, processes	reference/gotchas/by-language.md

Converting TO

Target	Key Considerations	Reference
Rust	Ownership, borrowing	reference/memory-ownership.md
Go	Simplicity, explicit errors	reference/error-handling.md
Python	Dynamic typing	reference/type-system-translation.md
Elixir	Functional, BEAM	reference/paradigm-translation.md

---

References

Related Skills

• meta-convert-dev - For creating new convert-X-Y skills
• convert-typescript-rust - TypeScript → Rust conversion
• convert-python-rust - Python → Rust conversion
• convert-golang-rust - Go → Rust conversion

Language Skills

For language-specific fundamentals (not conversion):

• lang-typescript-dev - TypeScript development patterns
• lang-python-dev - Python development patterns
• lang-rust-dev - Rust development patterns
• lang-elixir-dev - Elixir development patterns