read PEG file and generate a D parser for it with pegged

pegd.d

/+dub.json:
{
    "authors": ["dk949" ],
    "copyright": "Copyright © 2022, dk949",
    "dependencies": { "pegged": "~>0.4.6" },
    "description": "compiler for standalone pegged grammars",
    "license": "BSL-1.0",
    "name": "pegd"
}
+/
import pegged.grammar;
import std.file;
import std.path;
import std.stdio;

int main(string[] args) {
    string input;
    string output = "parser";
    switch (args.length) {
        case 3:
            output = args[2];
            goto case;
        case 2:
            input = args[1];
            break;
        case 0:
            args ~= "[APPLICATION_NAME]";
            goto default;
        default:
            stderr.writeln("Usage: ", baseName(args[0]), " INPUT_FILE [OUTPUT_FILE]");
            return 1;
    }
    if (output.length >= 2 && output[$ - 2 .. $] == ".d")
        output.length -= 2;
    if (output == "") {
        stderr.writeln(
            "output file name has to not be enmpty (and cannot contain just the extension)");
        return 1;
    }

    try
        asModule(baseName(output), output, readText(input));
    catch (Exception e) {
        stderr.writefln("Error: ", e.message);
        return 1;
    }
    return 0;
}