Language extensions

Language extensions provide the emit, build, and run steps for a specific target language. plcc-ng ships with Python, Java, JavaScript, and Haskell support.

How language extensions plug in

When plcc-make (or any command that calls it) builds a spec with a semantic section, it runs three dispatch commands in sequence:

1. plcc-lang-emit --target=LANG — calls plcc-<lang>-emit
2. plcc-lang-build --target=LANG — calls plcc-<lang>-build (no-op if not found)
3. plcc-lang-run --target=LANG — calls plcc-<lang>-run

The LANG value comes from the language declaration in the spec's semantic section. Use plcc-lang-list to see what is installed.

plcc-python

Emits a Python interpreter from model JSON, then runs it with the system Python.

Command	What it does
plcc-python-emit	Writes .py class files and a main.py entry point to the output directory
plcc-python-run	Runs main.py with the system Python interpreter

No build step is required for Python — plcc-lang-build exits silently if plcc-python-build is not found.

plcc-java

Emits a Java interpreter from model JSON, compiles it with javac, then runs it with java.

Command	What it does
plcc-java-emit	Writes .java class files and a Main.java entry point to the output directory
plcc-java-build	Compiles all .java files with javac; requires Java JDK 21+ on PATH
plcc-java-run	Runs Main with java; requires Java JDK 21+ on PATH

plcc-javascript

Emits a JavaScript interpreter from model JSON, then runs it with Node.js. No build step is required.

Command	What it does
plcc-javascript-emit	Writes .js class files and a main.js entry point to the output directory
plcc-javascript-run	Runs main.js with node; requires Node.js 18+ on PATH

No build step is required for JavaScript — plcc-lang-build exits silently if plcc-javascript-build is not found.

plcc-haskell

Emits a Haskell interpreter from model JSON, compiles it with cabal, then runs it with cabal run.

Command	What it does
plcc-haskell-emit	Writes .hs source files and an interpreter.cabal project file to the output directory
plcc-haskell-build	Compiles with cabal build; requires GHC 9.4+ and cabal 3.0+ on PATH
plcc-haskell-run	Runs cabal run interpreter; requires cabal 3.0+ on PATH

The _run() protocol

Every language extension's main/entry-point driver must implement the same contract for the root node's entry point method (_run() by default, or a custom name from entry_point):

• It returns a string. The driver marshals it into a {"kind": "result", "value": "<string>"} JSON record on stdout for plcc-rep to read and print — it does not print or convert the value itself.
• If it returns anything other than a string (or, for statically-typed languages, if the call otherwise fails to produce one — e.g. Java's reflection returning null), the driver raises a specification_error. It must never let a wrong-typed value flow into the value field silently.
• The entry-point implementation itself must never write to stdout. Doing so bypasses the JSON envelope entirely. plcc-rep echoes unparseable lines as-is, so the stray text surfaces in every verbose format — and under plcc-rep --verbose-format=json it lands among the JSON records as a line that is not JSON, breaking consumers that parse the stream.

This is what lets plcc-rep --verbose-format=json show a real, structured record for every result, regardless of which language emitted the interpreter. A new language extension must follow it to interoperate correctly with plcc-rep.