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name: transmute locale: caveman source_locale: en source_commit: 82c77053 fence_basis_commit: 82c77053 translator: "Julius Brussee homage — caveman" translation_date: "2026-05-03" description: > Transform a single function, module, or data structure from one form to another while preserving its essential behavior. Lighter-weight than the full athanor cycle, suitable for targeted conversions where the input and output forms are well-understood. Use when converting a function between languages, shifting a module between paradigms, migrating an API consumer to a new version, converting data formats, or replacing a dependency — when the transformation scope is a single function, class, or module rather than a full system. license: MIT allowed-tools: Read Write Edit Bash Grep Glob metadata: author: Philipp Thoss version: "1.0" domain: alchemy complexity: intermediate language: multi tags: alchemy, transmutation, conversion, refactoring, transformation, targeted

Transmute

Transform specific piece of code or data from one form to another — language translation, paradigm shift, format conversion, or API migration — while preserving essential behavior and semantics.

When Use

• Convert function from one language to another (Python to R, JavaScript to TypeScript)
• Shift module from one paradigm (class-based to functional, callbacks to async/await)
• Migrate API consumer from v1 to v2 of external service
• Convert data between formats (CSV to Parquet, REST to GraphQL schema)
• Replace dependency with equivalent (moment.js to date-fns, jQuery to vanilla JS)
• Transformation scope is single function, class, or module (not full system)

Inputs

• Required: Source material (file path, function name, or data sample)
• Required: Target form (language, paradigm, format, or API version)
• Optional: Behavioral contract (tests, type signatures, or expected I/O pairs)
• Optional: Constraints (must maintain backward compatibility, performance budget)

Steps

Step 1: Analyze Source Material

Understand exact what source does before attempting transformation.

1. Read the source completely — every branch, edge case, and error path
2. Identify the behavioral contract:
   • What inputs does it accept? (types, ranges, edge cases)
   • What outputs does it produce? (return values, side effects, error signals)
   • What invariants does it maintain? (ordering, uniqueness, referential integrity)
3. Catalog dependencies: what does the source import, call, or rely on?
4. If tests exist, read them to understand expected behavior
5. If no tests exist, write behavioral characterization tests before transmuting

Got: Complete understanding of what source does (not how it does it). Behavioral contract explicit and testable.

If fail: Source too complex for single transmute? Consider breaking into smaller pieces or escalating to full athanor procedure. Behavior ambiguous? Ask for clarification rather than guessing.

Step 2: Map Source to Target Form

Design transformation mapping.

1. For each element in the source, identify the target equivalent:
   • Language constructs: loops → map/filter, classes → closures, etc.
   • API calls: old endpoint → new endpoint, request/response shape changes
   • Data types: data frame columns → schema fields, nested JSON → flat tables
2. Identify elements with no direct equivalent:
   • Source features missing in target (e.g., pattern matching in a language without it)
   • Target idioms that don't exist in source (e.g., R's vectorization vs. Python loops)
3. For each gap, choose an adaptation strategy:
   • Emulate: reproduce the behavior with target-native constructs
   • Simplify: if the source construct was a workaround, use the target's native solution
   • Document: if behavior changes slightly, note the difference explicitly
4. Write the transformation map: source element → target element, for every piece

Got: Complete mapping where every source element has target destination. Gaps identified and adaptation strategies chosen.

If fail: Too many elements lack direct equivalents? Transformation may be inappropriate (e.g., transmuting highly object-oriented design into language without classes). Reconsider target form or escalate to athanor.

Step 3: Execute Transformation

Write target form following map.

1. Create the target file(s) with appropriate structure and boilerplate
2. Transmute each element following the map from Step 2:
   • Preserve the behavioral contract — same inputs produce same outputs
   • Use target-native idioms rather than literal translations
   • Maintain or improve error handling
3. Handle dependencies:
   • Replace source dependencies with target equivalents
   • If a dependency has no equivalent, implement a minimal adapter
4. Add inline comments only where the transformation was non-obvious

Got: Complete target implementation follows transformation map. Code reads like written native in target form, not mechanical translated.

If fail: Specific element resists transformation? Isolate it. Transform everything else first, then tackle resistant element with focused attention. Truly cannot be transmuted? Document why, provide workaround.

Step 4: Verify Behavioral Equivalence

Confirm transmuted form preserves original's behavior.

1. Run the behavioral contract tests against the target implementation
2. For each test case, verify:
   • Same inputs → same outputs (within acceptable tolerance for numeric conversions)
   • Same error conditions → equivalent error signals
   • Side effects (if any) are preserved or documented as changed
3. Check edge cases explicitly:
   • Null/NA/undefined handling
   • Empty collections
   • Boundary values (max int, empty string, zero-length arrays)
4. If the target form adds capabilities (e.g., type safety), verify those too

Got: All behavioral contract tests pass. Edge cases handled equivalent. Any behavioral differences documented and intentional.

If fail: Tests fail? Diff source and target behavior to find divergence. Fix target to match source contract. Divergence intentional (e.g., fixing bug in original)? Document explicit.

Checks Checklist

• Source material full analyzed with explicit behavioral contract
• Transformation map covers every source element
• Gaps identified with adaptation strategies documented
• Target implementation uses native idioms (not literal translation)
• All behavioral contract tests pass against target
• Edge cases verified (null, empty, boundary values)
• Dependencies resolved with target equivalents
• Any behavioral differences documented and intentional

Pitfalls

• Literal translation: Writing Python-in-R or Java-in-JavaScript instead of using target idioms. Result should look native
• Skip behavioral tests: Transmuting without tests means you cannot verify equivalence. Write characterization tests first
• Ignore edge cases: Happy path transmutes easy; edge cases are where bugs hide
• Over-engineer adapter: Dependency needs 200-line adapter? Transmutation scope too large
• Transmute comments verbatim: Comments should explain target code, not echo source. Rewrite them

See Also

• athanor — Full four-stage transformation for systems too large for single transmute
• chrysopoeia — Optimizing transmuted code for maximum value extraction
• review-software-architecture — Post-transmutation architecture review for larger conversions
• serialize-data-formats — Specialized data format conversion procedures