How to Enable and Configure Debug Logging Using the curryhoward.log JVM Property

Set the JVM system property curryhoward.log to a comma-separated list of options (prover, trace, macros, verbose, terms) to activate specific debug output channels in the CurryHoward library.

The chymyst/curryhoward library uses a centralized logging mechanism controlled entirely by the curryhoward.log JVM property. When you enable and configure debug logging using the curryhoward.log JVM property, the library parses the value at runtime in src/main/scala/io/chymyst/ch/Macros.scala and activates targeted diagnostic output for theorem proving, macro expansion, and term generation.

Understanding the curryhoward.log JVM Property

The property acts as a comma-delimited flag parser. In Macros.scala (lines 497–503), the private options method reads the system property, splits it on commas, and converts the tokens to a Set[String]:

private[ch] def options: Set[String] = 
  Option(System.getProperty("curryhoward.log")).getOrElse("")
        .split(",")
        .toSet

Each token in the set toggles a specific boolean debug flag elsewhere in the codebase. If the property is undefined, the set is empty and all debug output remains silent.

Available Debug Options

The library recognizes five distinct logging tokens. Each maps to a specific boolean value that guards println or c.info statements.

prover

Enables TheoremProver.debug (line 9 of TheoremProver.scala). When active, the theorem-prover engine emits detailed proof-search diagnostics, including sequent transformations and final proof term counts.

trace

Activates TheoremProver.debugTrace (line 11 of TheoremProver.scala). This option adds timing data and intermediate sequent snapshots to the prover output, useful for performance analysis.

macros

Controls Macros.debug (line 42 of Macros.scala). This flag prints debug messages during macro expansion, showing how the library translates Scala types into logical propositions.

verbose

Drives Macros.verbose (line 44 of Macros.scala). A more detailed variant of macros, this outputs additional internal state during macro processing.

terms

Toggles Macros.showReturningTerm (line 46 of Macros.scala). When enabled, the macro prints the generated lambda term before returning it to the compiler, letting you inspect the synthesized code.

How to Set the curryhoward.log Property

You can configure the property either via the JVM command line or programmatically within your Scala application.

Command-Line Configuration with sbt

Pass the property to the JVM through sbt’s -D flag. For example, to enable prover debug output during a specific test:

sbt "testOnly io.chymyst.ch.unit.MiscSpec -- -Dcurryhoward.log=prover"

To combine multiple options, separate them with commas (no spaces):

sbt -Dcurryhoward.log=macros,terms run

For full trace output alongside prover diagnostics:

sbt -Dcurryhoward.log=prover,trace test

Programmatic Configuration in Scala

You can also set the property from within your code, which is useful in test suites or REPL sessions. The test suite in MiscSpec.scala (lines 54–66) demonstrates this pattern:

// Enable debug logging before invoking macros
System.setProperty("curryhoward.log", "macros,terms")

// ... invoke CurryHoward macros ...

// Clean up after the test
System.clearProperty("curryhoward.log")

Similarly, LJTSpec3.scala (lines 34–36) shows combined usage:

System.setProperty("curryhoward.log", "prover,macros,terms,trace")

Summary

• The curryhoward.log JVM property accepts a comma-separated list of debug tokens parsed in Macros.scala.
• Five options control output: prover and trace for theorem-prover diagnostics (TheoremProver.scala), and macros, verbose, and terms for macro expansion details (Macros.scala).
• Configure the property via sbt command line (-Dcurryhoward.log=option1,option2) or programmatically using System.setProperty.

Frequently Asked Questions

What happens if I set an unsupported option in curryhoward.log?

The library silently ignores any token that does not match the known set. The options method in Macros.scala simply converts the split strings to a Set[String]; downstream checks look for specific keys, so unknown values have no effect and produce no warnings.

Can I enable all debug output at once?

There is no single "all" token. To capture every diagnostic channel, you must explicitly list all five options: prover,trace,macros,verbose,terms. For example: sbt -Dcurryhoward.log=prover,trace,macros,verbose,terms test.

Does the curryhoward.log property affect runtime performance?

Yes, but only when specific options are active. The library guards expensive debug logic with boolean checks (e.g., if (TheoremProver.debug) ...). When the property is unset or empty, these booleans are false and the compiler optimizes away the debug code paths, resulting in zero overhead.

Where can I see examples of debug logging in the test suite?

The test files MiscSpec.scala and LJTSpec3.scala demonstrate programmatic configuration. MiscSpec.scala (lines 54–66) shows setting and clearing the property around a test case, while LJTSpec3.scala (lines 34–36) enables multiple options before running theorem-prover tests.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}