Syntax highlighting added to Canto34

I’ve just extended my parser toolkit, canto34. Canto 34 is a library for building recursive-descent parsers. It can be used both on node.js, and in the browser as an AMD module.

Starting in v0.0.5, I’ve added a function to let you generate a `.tmLanguage` file. This is the syntax highlighting system of TextMate, Sublime Text, Atom, and Visual Studio code.

This is actually pretty sweet; it makes your language feel a bit more ‘first class’ when you get the richer IDE experience.

You first generate the file content, then save it wherever your text editor demands. For example, To use it with Sublime Text 3 on windows, call code like so, swapping `{myusername}` with the name of your user account;

 var content = canto34.tmLanguage.generateTmLanguageDefinition(lexer);    require(‘fs’).writeFileSync(“C:\\Users\\{myusername}\\AppData\\Roaming\\Sublime Text 3\\Packages\\User\\myparser.tmLanguage”, content);

This will write out a syntax highlighting file into your User folder, which is a personal ‘dumping ground’ for configuration bits and pieces on your machine for Sublime Text. When you restart ST, you’ll see your language in the list of language options, displayed in the bottom-right.

You’ll need to configure the tokens in your lexer a bit more. For example, if you have a variable name token, you’ll need to tell the lexer that this should be highlighted one way, and if you have a keyword like ‘for’, you’ll use another. Do this with the `roles` option on a token type;

    lexer.addTokenType({ name: “comment”, ignore: true, regexp: /^#.*/, role: [“comment”, “line”] });

lexer.addTokenType(types.constant(“for”,”for”, [“keyword”]));

lexer.addTokenType(types.constant(“[“, “openSquare”, [“punctuation”]));

lexer.addTokenType(types.constant(“]”, “closeSquare”, [“punctuation”]));

The list of roles isn’t clear to me – I’ve just figured out some key ones like `keyword`, `comment`, and `punctuation` from reverse engineering existing `tmLanguage` files.

Find out more on GitHub or NPM.

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Pretty-printing recordsets from the mssql node package

I’ve been using the node mssql package in node scripts, and it’s great but it doesn’t have a pretty-printer for recordsets; console.dir() will print something out but you get some nasty-looking JSON formatted output.

This function is just a reusable printer for recordsets returned from sql.Request().query() or sql.Request().batch().methods.

Pass in the recordset and a function which prints the line, eg;

printTable(recordset, console.log);

And you get something more famililar with a SQL Server Management Studio feel;

-- SELECT id, name from table
id   name
===========
6    p1
7    p2
8    p3

Here’s the function:

// pretty-print a table returned from mssql node package 
// https://www.npmjs.com/package/mssql
var printTable = function(recordset, printLine) {

 var padEnd = function (str, paddingValue) {
   while(str.length < paddingValue) {
     str = str + " ";
   }
   return str;
 };

 var print = function(value) {
   return (value == undefined || value == null) ? "(null)" : value.toString(); 
 }

 var maxWidth = {};

 for(var c in recordset.columns) {
   maxWidth[c] = c.length;
 }

 var l = recordset.length;
 for(var r = 0; r < l; r++) {
   var row = recordset[r];
   for(var c in recordset.columns) {
     var col = recordset.columns[c];
     row[c] = print(row[c]);
     maxWidth[c] = Math.max(maxWidth[c], row[c].length);
   }
 }

 var head = "";
 for(var c in recordset.columns) {
   var head = head + padEnd(c, maxWidth[c]) + " ";
 }

 printLine(head);

 var sep = Array(head.length).join("=");
 
 printLine(sep);

 for(var r = 0; r < l; r++) {
   var row = recordset[r];
   var printedRow = "";
   for(var c in recordset.columns) {
     printedRow = printedRow + padEnd(row[c], maxWidth[c]) + " ";
   }
   printLine(printedRow);
 }
};

Calculating expected finger table entries for virtual ring distributed systems like Chord and Cassandra

Here’s a block of code I wrote to print out finger tables for Chord-like distributed hash tables. Just update the ‘nodes’ variable and the m-value to adjust to any system. Runs happily in Node.js 4.4.0.

// calculating finger tables for Chord-like distributed hash table.

// the size of the ring, as 2^m;
var m=9, ringSize = Math.pow(2,m);

// the nodes we know about
var nodes = [1, 12, 123, 234, 345, 456, 501]; 

// just make sure it's sorted
nodes = nodes.sort( (a,b) => a-b );

console.log('the finger tables for a ', ringSize,'-virtual-node system');
console.log('========');
console.log('nodes: ', nodes);

// calculate the finger table for each node
nodes.forEach(n => {

 var fingerTable = [];
 i = 1;
 for(var x = 0; x < m; x++) {
 var nodeId = (n + i) % ringSize;
 // find the node after nodeId; 
 var ftEntry = nodes.filter(x => x > nodeId).concat(nodes)[0];
 fingerTable.push(ftEntry);
 i = i << 1;
 }
 
 console.log(n + ':', fingerTable);
});