Brandon Lucas
9511957076
Add support for the `resume(value)` expression in effect handler
bodies. When resume is called, the value becomes the return value
of the effect operation, allowing handlers to provide values back
to the calling code.
Implementation:
- Add Resume(Value) variant to EvalResult
- Add in_handler_depth tracking to Interpreter
- Update Expr::Resume evaluation to return Resume when in handler
- Handle Resume results in handle_effect to use as return value
- Add 2 tests for resumable handlers
Example usage:
```lux
handler prettyLogger: Logger {
fn log(level, msg) = {
Console.print("[" + level + "] " + msg)
resume(()) // Return Unit to the call site
}
}
```
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
46 lines
1.2 KiB
Plaintext
46 lines
1.2 KiB
Plaintext
// Demonstrating resumable effect handlers in Lux
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//
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// Handlers can use `resume(value)` to return a value to the effect call site
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// and continue the computation. This enables powerful control flow patterns.
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//
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// Expected output:
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// [INFO] Starting computation
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// [DEBUG] Intermediate result: 10
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// [INFO] Computation complete
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// Final result: 20
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// Define a custom logging effect
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effect Logger {
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fn log(level: String, msg: String): Unit
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fn getLogLevel(): String
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}
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// A function that uses the Logger effect
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fn compute(): Int with {Logger} = {
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Logger.log("INFO", "Starting computation")
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let x = 10
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Logger.log("DEBUG", "Intermediate result: " + toString(x))
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let result = x * 2
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Logger.log("INFO", "Computation complete")
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result
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}
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// A handler that prints logs with brackets and resumes with Unit
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handler prettyLogger: Logger {
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fn log(level, msg) = {
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Console.print("[" + level + "] " + msg)
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resume(())
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}
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fn getLogLevel() = resume("DEBUG")
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}
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// Main function
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fn main(): Unit with {Console} = {
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let result = run compute() with {
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Logger = prettyLogger
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}
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Console.print("Final result: " + toString(result))
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}
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let output = run main() with {}
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