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Language Guide

A plcc-ng specification describes a language's tokens, syntax, and semantics.

# Lexical section
skip WHITESPACE /\s+/
token NUM /\d+/

%

# Syntactic section
<Exp> ::= <NUM>

%

# Semantic section
Python

Exp
%%%
def _run(self):
    print("Hello")
%%%

# Lexical section
skip WHITESPACE /\s+/
token NUM /\d+/

%

# Syntactic section
<Exp> ::= <NUM>

%

# Semantic section
Java

Exp
%%%
public void _run() {
    System.out.println("Hello");
}
%%%

Comments

Comments start with # and end at the end of the current line. Comments may appear anywhere except in semantic section code blocks.

Section separators

Each section is separated by a line with a single %.

Includes

Although you can define an entire language in a single file, larger languages are often easier to maintain when split across multiple files using the %include statement.

%include FILE_PATH

%include is valid in any section, but may not appear in a code block within the semantic section. FILE_PATH is relative to the directory containing the file it appears in.

Optional sections

Sections build on one another:

LexicalSyntacticSemantictokens/terminalsclass hiearchy

You can start with only a lexical section (no % separator is needed), or add a syntactic section without defining semantics. This makes it easy to develop and test a language incrementally.

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