zo

What is zo?

Zo is a asynchronous query language providing the usual functional programming list operators like map, select and reduce, but all in an async-friendly style, so they're ready to use while performing async IO operations in node.js.

Installation

npm install zo

Operation

require

var zo = require('zo').zo;

map

zo([1, 2, 3])
.map(function (item, mapTo) {
process.nextTick(function () {
mapTo(item + 1);
});
})
.results(function (mappedItems) {
console.log(mappedItems);
});

Produces: [ 2, 3, 4 ]

select

zo([1, 2, 3])
.select(function (item, selectIf) {
process.nextTick(function () {
selectIf(item > 1);
});
})
.results(function (selectedItems) {
console.log(selectedItems);
});

Produces: [ 2, 3 ]

reduce (also foldl)

zo([1, 2, 3])
.reduce(0, function (sum, item, reduceInto) {
process.nextTick(function () {
reduceInto(sum + item);
});
})
.results(function (sum) {
console.log(sum);
});

Produces: 6

See also reduceRight, which is a synonym for foldr

each

zo([1, 2, 3])
.each(function (item, done) {
process.nextTick(function () {
console.log('item: ' + item);
done();
});
})
.results(function (items) {
console.log('count: ' + items.length);
});

Produces:

item: 1
item: 2
item: 3
count: 3

Async IO

But the whole point is when you mix it with async IO:

var fs = require('fs');
var zo = require('zo').zo;
fs.readdir('.', function (err, filesAndDirectories) {
zo(filesAndDirectories)
.map(function (file, mapTo) {
fs.stat(file, function (err, stat) {
mapTo({file: file, stat: stat});
});
})
.select(function (fileAndStat, selectIf) {
selectIf(fileAndStat.stat.isFile() && !/^\./.test(fileAndStat.file));
})
.map(function (fileAndStat, mapTo) {
mapTo(fileAndStat.file + ': ' + fileAndStat.stat.size + ' bytes');
})
.each(function (fileWithSize, done) {
console.log(fileWithSize);
done();
})
.results(function (files) {
console.log();
console.log(files.length + ' files');
});
});