kylediaz/peg2antlr

peg2antlr

peg and ANTLR are tools that generate parsers from grammar files. This program translates the syntax from pointlander/peg-style grammar to antlr g4 style.

Usage

go run ./ peg_input.peg [antlr_output]

Creates antlr_outputLexer.g4 and antlr_outputLexer.g4

How it works

1. The peg repository has a grammar for the peg language. I used that to generate a parser for .peg files.
2. Parse the peg file, turning it into an AST
3. Traverse the AST and index the tokens used in the peg grammar file so we can know what Lexer definitions we need.
4. Compile the AST into a ANTLR-style grammar file using various rules.
   • For example, grammar rule definitions in peg are label <- expression while in ANTLR it's label: expression. This can easily be translated by switching out the symbol.
   • This rules can be more advanced, such as how it handles regex. ANTLR's regex engine has less features than peg's, so it requires a little more elbow grease.

Credits

peg_grammar.peg, the grammar file used to parse .peg files, is shamelessly stolen from the pointlander/peg repo