Petar

PETAR is a DSL used to produce annotated representation from tree-like data.

This document explains how to use the CLI for the java interpreter.

This tool is distributed as a JAR file and is executed via java -jar.

If you want to understand more about the Petar language go to the Petar language specification.

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Requirements

• Java 17+ recommended
• A valid PETAR .jar file

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Basic Usage

java -jar petar.jar --spec <spec-files> -r <root type> [options]

At minimum, you must provide at least one specification file using --spec or -s.

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Command Options

Required

--spec / -s

Provide one or more specification files.

-s file1.petar file2.petar
--spec file1.petar file2.petar

• Type: List<File>
• Required: ✅ Yes

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-r

Root type to use for interpretation. This defines the entry point type used when interpreting the input tree.

-r Expression

• Type: String
• Required: ✅ Yes

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Optional

-i

Input file to process.

-i input.json

• Type: File

If this is not specified the interpreter will parse and check the specification files provided. This can be used to typecheck or namecheck Petar programs indecently from data.

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-o

Output file for results.

-o output.json

• Type: File

If omitted, output will be printed to standard output.

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-p

Print the loaded specification.

-p

• Type: Boolean
• Default: false

Useful for debugging and verifying that your .petar specification files are correctly loaded.

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--help

Displays help information about available commands.

--help

• Type: Boolean
• Default: false

When enabled, the program will print usage information and exit.

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Examples

1. Basic execution

java -jar petar.jar \
  --spec rules.petar \
  -i input.json \
  -o output.json \
  -r Expression

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2. Multiple specification files

java -jar petar.jar \
  --spec base.petar transformations.petar \
  -i input.json \
  -o output.json

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3. Print specification only (debug mode)

java -jar petar.jar \
  --spec rules.petar \
  -p

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4. Minimal execution (stdout output)

java -jar petar.jar \
  --spec rules.petar \
  -i input.json

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Behavior Overview

When executed, PETAR performs the following steps:

1. Loads all specification files (--spec) and check it
2. Parses the input tree (-i) and check the root type (-r)
3. Applies pattern matching rules
4. Generates annotations via production rules
5. Writes results to output (-o) or stdout

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Notes

• Multiple --spec files are merged into a single rule set.
• The order of specification files should not the output.
• If no -o is provided, output defaults to standard output.

Help

Run:

java -jar petar.jar --help

for built-in usage information.