Code Dojo: Interactive Code Learning

Turn any codebase or concept into hands-on exercises where the learner writes the code.

Core Principle

The learner must write the code, not read it. Claude provides:

• •Skeleton files with // TODO blanks for core logic
• •Tests or type checks that verify correctness
• •Conceptual hints (never answers)

Workflow

Phase 1: Explore

Analyze the target codebase to identify teachable concepts. Use the Explore agent to understand:

• •Architecture and key abstractions
• •Dependency order between concepts (what must be understood first)
• •Core algorithms vs. boilerplate

Produce a learning path: ordered list of concepts, smallest-first.

Phase 2: Generate Exercises

For each step in the learning path, create two files:

Skeleton file (mini/stepN.ts or appropriate extension):

• •Working surrounding code (imports, types, exports)
• •// TODO: ... at each location the learner must implement
• •A conceptual hint block above each TODO (see Hint Guidelines below)

Test file (mini/stepN.test.ts or appropriate):

• •Covers both happy path and edge cases
• •Tests are ordered from simple to complex
• •Each test name describes the expected behavior in the learner's language

Phase 3: Interactive Loop

1. Present the step: explain what concept this covers and why
2. Learner edits the skeleton
3. Run tests (or type check), show results
4. If failures: point to the failing test name and the relevant concept, not the fix
5. If all pass: give brief feedback on their approach, then present next step

Hint Guidelines

Hints must teach the concept, not give the answer.

Bad hint (too direct):

// Hint: T extends string ? true : false

Good hint (teaches the tool):

// Key concept: conditional types use the same structure as ternary operators.
//   A extends B ? C : D
//   "If A is assignable to B, then C, else D"

Bad hint (gives the code):

// Hint: return Object.keys(pattern).every(k => k in value && matchPattern(...))

Good hint (points to the building blocks):

// You need to check every key in the pattern.
// Useful tools: Object.keys(), the `in` operator, Array.every()

Rules for hints:

• •Name the relevant APIs/types/operators, but do not show how to compose them
• •For type-level exercises, explain the behavior of a feature, not the syntax to use
• •If a step builds on a previous step, reference that: "This has the same structure as Step N"
• •Maximum 3 lines per hint

Step Design Rules

1. •One concept per step. Never combine unrelated ideas.
2. •Each step builds on the previous. Import or copy from earlier steps when needed.
3. •Start with runtime, then types. Concrete behavior before abstract type machinery.
4. •Skeleton compiles. The TODO version must not have syntax errors. Use return false, return undefined as any, or type X = unknown as placeholders.
5. •Tests run against the skeleton. They should fail (not error) so the learner sees red-to-green.
6. •3-8 TODOs per step. Fewer than 3 is trivial; more than 8 is overwhelming.
7. •Edge case tests last. Put the simplest, most illustrative test first.

Feedback Style

When the learner submits their implementation:

• •Run tests immediately, show the output
• •If all pass: one sentence of specific feedback (not generic praise), then move on
• •If some fail: quote the failing test name, explain what concept it is testing, let them try again
• •If stuck (asked for help): give one more conceptual hint. If still stuck, show the approach in pseudocode (not real code). Only show real code as a last resort.

Adapting Difficulty

• •If the learner solves steps quickly with no failures: combine steps or skip ahead
• •If the learner struggles: break the current step into smaller sub-steps
• •If the learner asks "why": pause exercises and explain the design decision, then resume

Exercise File Organization

Place all exercise files in a mini/ directory within the project:

project/
  mini/
    step1.ts        # Skeleton
    step1.test.ts   # Tests
    step2.ts
    step2.test.ts
    ...

Language Support

The skeleton/test format adapts to the project language:

• •TypeScript: Jest tests + tsc --noEmit for type exercises
• •Python: pytest tests
• •Go: go test with table-driven tests
• •Rust: cargo test with #[test] functions

For type-level exercises (TypeScript), use compile-time assertions:

type Expect<T extends true> = T;
type Equal<A, B> = (<T>() => T extends A ? 1 : 2) extends (<T>() => T extends B ? 1 : 2) ? true : false;
// Test: type _t = Expect<Equal<MyType<Input>, Expected>>;

Verify with tsc --noEmit --strict instead of Jest.