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Scanners

A set of high performance Scanners implemented in C# for low-level text/script parsing.

Nuget

Scanner overview

A Scanner is used to scan over and extract Tokens from text, check for strings or characters (delimiters), skip over text etc.

Tokens represent basic units of meaning in the input source code, such as keywords, identifiers, operators and special characters.

The library provides associated utilities and low level scanners (extensible) with a comprehensive set of methods. See the following reference documents for details:

  • TextScanner: Primary core text scanning facilities.
  • ScriptScanner: Extends TextScanner with facilities useful for scanning scripts .
  • ScanErrorLog: Class to log and output scan error messages.
  • ILogScanError: Interface to allow external entities to log errors in ScanErrorLog.

Simple scanning example:

using Psw.Scanners;

bool ScanSample() {
    var sample = " FuncName (prm1, 'prm2') { sample body }"; // Text to parse
    var scn = new ScriptScanner(sample);

    // Use the scanner ErrorLog for formatted error reporting
    bool Error(string msg) {
        scn.LogError(msg);
        Console.WriteLine(scn.ErrorLog.AsConsoleError("Sample Error"));
        return false;
    }

    scn.SkipSp();
    if (!scn.StdIdent()) return Error("Function name expected");
    var funcName = scn.Token;

    scn.SkipSp();
    if (!scn.IsPeekCh('(')) return Error("( expected");

    var prm = scn.ScanList();
    if (prm == null) return Error("Parameters expected");

    scn.SkipSp();
    if (!scn.IsPeekCh('{')) return Error("{ expected");

    if (!scn.ScanBlock()) return Error("body expected");
    var body = scn.TrimToken;

    Console.WriteLine($"Result: {funcName}({string.Join(',', prm)}) {{{body}}}");
    return true;
}

Sample output:

Result: FuncName(prm1,prm2) {sample body}

Or for an Error: 
Sample Error
 FuncName (prm1, 'prm2')  sample body }
--------------------------^ (Ln:1 Ch:27)
Parse error: { expected

FYI: the above parsing can be implemented using Flow Expressions

Flow Expressions are a powerful and novel mechanism for building complex inline Parsers and other logical flow systems.

void FexScanSample() {
    var fex = new FexParser(" FuncName (prm1, 'prm2') { sample body }");
    string funcName = "", body = "";
    List<string> prm = null;

    var funcParse = fex.Seq(s => s.GlobalPreOp(c => c.SkipSp())
        .StdIdent().ActToken(t => funcName = t).OnFail("Function name expected")
        .PeekCh('(').OnFail("( expected")
        .ScanList().ActValue<List<string>>(v => prm = v).OnFail("Parameters expected")
        .PeekCh('{').OnFail("{ expected")
        .ScanBlock().ActTrimToken(t => body = t));

    Console.WriteLine(fex.Run(funcParse, () => $"Result: {funcName}({string.Join(',', prm)}) {{{body}}}", e => e.AsConsoleError("Error")));
}