dabscm

A Scheme R7RS interpreter with parallel implementations in C# (.NET 10) and Java 11. The two implementations share a common library.scm and a common set of .sld library files, kept in sync from a single source of truth.

Features

• R7RS-small core
• Bytecode VM (tokenizer → compiler → VM) mirrored in C# and Java
• A JIT that compiles hot procedures to JVM bytecode or .NET IL
• Module system with scheme (R7RS) and scm (extensions) libraries
• 22 SRFI implementations (1, 2, 8, 9, 13, 14, 18, 19, 26, 28, 39, 64, 69, 95, 98, 111, 125, 128, 132, 133, 151, 158)
• Sets-of-scopes hygienic macro expander (Flatt, POPL 2016)
• ~4500 test assertions across R7RS, SRFI, and feature suites

Layout

• scm-lib/ — source of truth for library.scm and .sld library files
• scm-tests/ — source of truth for tests (core/, tests/, failures/)
• scm-csharp/ — C# implementation (scheme/, repl/, tests/)
• scm-java/ — Java implementation
• documentation/ — generated API documentation
• examples/ — example scripts
• scm-bootstrap.jar — bootstrap interpreter used by the build scripts

Building

The build system is Scheme-based: builder.sh (or builder.bat) runs java -jar scm-bootstrap.jar against a .scm build script.

# Sync library and test files from source-of-truth to both implementations
./builder.sh update-scheme-files.scm

# C#: build / test / build+test
./builder.sh build-scm-csharp.scm
./builder.sh test-scm-csharp.scm
./builder.sh build-and-test-scm-csharp.scm

# Java: build / test / build+test
./builder.sh build-scm-java.scm
./builder.sh test-scm-java.scm
./builder.sh build-and-test-scm-java.scm

# Update documentation (needs an up-to-date scm-java/scm.jar)
./builder.sh update-documentation.scm

# Full rebuild: sync, build+test both, regenerate documentation
./builder.sh rebuild-all.scm

Do not run the C# and Java test suites in parallel — they share files and directories in the temp folder and will collide.

Requirements:

• .NET 10 SDK (dotnet)
• JDK 11 or later (java, javac, jar)

Running

After building, the C# executable is scm and the Java jar is scm.jar.

scm -e 'CODE'       # eval CODE with minimal imports
scm -b 'CODE'       # eval CODE with no imports (useful for debugging base)
scm -f 'CODE'       # eval CODE with full REPL imports
scm script.scm      # run a script (in `user program`, no auto-imports)
scm                 # start a REPL (in `user main`, REPL auto-imports)

JIT

Both implementations compile a procedure to the platform's own code (JVM bytecode, .NET IL) once the interpreter has called it 100 times; the JVM or .NET JIT then compiles it like any other code. Long-running programs (servers, large batch runs) gain the most, short runs hardly at all. It is controlled by system properties (Java) or environment variables (C#):

Java	C#
-Dscm.jit=off	SCM_JIT=off	interpreter only
-Dscm.jit.threshold=0	SCM_JIT_THRESHOLD=0	compile on the first call
-Dscm.jit.stats=true	SCM_JIT_STATS=true	print counters at exit
-Dscm.jit.debug=true	SCM_JIT_DEBUG=true	report compiled/rejected code

java -Dscm.jit=off -jar scm.jar script.scm
SCM_JIT=off scm script.scm

The generated code is verified Java 11 class files, or IL in a dynamic assembly, loaded by the platform's standard mechanisms. No native code is generated by dabscm itself and no runtime flags are needed.

License

MIT — see LICENSE. Third-party code and academic influences are documented in ACKNOWLEDGMENTS.md.