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name: cljr-feature-dev description: Develop features for the Cljr Clojure-to-.NET compiler. Use when adding emitter features, expression types, analyzer support, or testing features. Guides the complete workflow from Expr.cs to C# tests to NRepl verification. Critical for REPL-oriented development.

Cljr Feature Development

This skill guides you through the complete workflow for adding features to the Cljr compiler, with proper testing in both C# unit tests and NRepl evaluation.

When to use this skill

• Adding new language features to the emitter
• Creating new expression types in the analyzer
• Modifying existing expression handling
• Testing features via C# unit tests
• Testing features via NRepl evaluation (CRITICAL for REPL-oriented workflow)

Feature Development Workflow

Step 1: Define Expression Type (if new)

Location: src/Cljr.Compiler/Analyzer/Expr.cs

Add a new record type extending Expr:

Copy/// <summary>
/// Description of what this expression represents
/// </summary>
public record MyFeatureExpr(
    string Property1,
    Expr Property2
) : Expr;

See expressions.md for all existing expression types.

Step 2: Add Analyzer Support

Location: src/Cljr.Compiler/Analyzer/Analyzer.cs

• Add case in AnalyzeForm() or AnalyzeSeq() to recognize the new form
• Build the expression AST
• Handle type hints and symbol resolution

Step 3: Add Emitter Support

Location: src/Cljr.Compiler/Emitter/CSharpEmitter.cs

• Add case to EmitExpr() switch statement
• Generate valid C# code for the expression

Copycase MyFeatureExpr e:
    EmitMyFeature(e);
    break;

Step 4: Write C# Unit Test for Compilation (REQUIRED)

Location: tests/Cljr.Compiler.Tests/

Test that the emitter generates correct C# code:

Copy[Fact]
public void MyFeature_EmitsCorrectCSharp()
{
    var source = "(my-feature args)";
    var result = Compile(source);
    Assert.Contains("expected C# output", result);
}

Step 5: Write C# Unit Test for NRepl Eval (REQUIRED)

Location: tests/Cljr.Compiler.Tests/ReplNamespaceTests.cs

This is CRITICAL for the REPL-oriented workflow. Test via NreplSession.EvalAsync():

Copy[Fact]
public async Task MyFeature_WorksInRepl()
{
    var session = new NreplSession();

    var result = await session.EvalAsync("(my-feature args)");

    Assert.Null(result.Error);
    Assert.Equal(expectedValue, result.Values[0]);
}

See testing-patterns.md for comprehensive test patterns including:

• State persistence across evaluations
• Namespace isolation
• Error handling

Step 6: Manual NRepl Verification (Optional)

Start the REPL and test interactively:

Copy./nrepl.sh
# or
dotnet run --project src/Cljr.Cli -- nrepl

Then test your feature in the REPL to verify developer experience.

Key Files

Testing Requirements

Every feature MUST have:

1. C# compilation test - Verify the emitter generates correct C#
2. C# NRepl eval test - Verify the feature works in REPL evaluation via NreplSession.EvalAsync()

The NRepl eval test is especially important because it ensures the feature works in the interactive REPL-oriented development workflow that Clojure developers expect.

Run Tests

Copy# Run all compiler tests
dotnet test tests/Cljr.Compiler.Tests/

# Run specific test
dotnet test tests/Cljr.Compiler.Tests/ --filter "MyFeature"

References

• Expression Types - All 30+ expression types in Expr.cs
• Testing Patterns - C# and NRepl test examples