This parser is a part of the compiler for the language "Context". You can watch the progress in the weekly german devlog on Youtube.

This is a linear LL(k)-parser with error-recovery which is able to transform a text into an abstract syntax tree (AST) based on the following rules:

This is the EBNF for a simple mathematical expression:

nr  := '-'? ('0' | ... | '9')+
op  := '+' | '-' | '*' | '/'
exp := nr (op nr)*

And this is the implementation with this library (the boolean-literal describes the optionality of the rule):

Rule nr  = new Pattern("-?[0-9]");
Rule op  = new Alteration(false, "+", "-", "*", "/");
Rule exp = new Ordered(nr, new Multiple(true, op, nr));

Now calling exp.tokenize("10 + -20 * 147") will yield the following tree:

"TokenArray": {
  "LiteralToken": "10",
  "TokenList": [
    "TokenArray": {
      "LiteralToken": "+",
      "LiteralToken": "-20"
    },
    "TokenArray": {
      "LiteralToken": "*",
      "LiteralToken": "147"
    }
  ]
}

Meanwhile calling exp.tokenize("10 xxx * 147") will result in:

"TokenArray": {
  "LiteralToken": "10",
  "TokenList": [
    "ErrorToken": "xxx", <-- Error
    "TokenArray": {
      "LiteralToken": "*",
      "LiteralToken": "147"
    }
  ]
}

This project requires:

• Java jdk18
• The helper-library