Dmitry Soshnikov DmitrySoshnikov

Pattern Matching

In this article we briefly describe the generic topic of pattern matching in programming languages. We'll see that this powerful technique is present in our every day programming, even if we may not notice it.

Matching

A matching is a process of checking whether one thing has the same or similar representation as another thing.

There are two basic matches:

Map.prototype.filter ( callbackfn [ , thisArg ] )

NOTE callbackfn should be a function that accepts three arguments. filter calls callbackfn once for each key/value pair present in the map object, in key insertion order, and returns a new filtered map. callbackfn is called only for keys of the map which actually exist; it is not called for keys that have been deleted from the map.

If a thisArg parameter is provided, it will be used as the this value for each invocation of callbackfn. If it is not provided, undefined is used instead.

callbackfn is called with three arguments: the value of the item, the key of the item, and the Map object being traversed.

filter does not directly mutate the object on which it is called but the object may be mutated by the calls to callbackfn.

Map.prototype.map ( callbackfn [ , thisArg ] )

The map method calls MapTransform abstract operation passing this value as M, callbackfn, thisArg as is, and false as updateKey.

The length property of the map method is 1.

Map.prototype.mapEntries ( callbackfn [ , thisArg ] )

The mapEntries method calls MapTransform abstract operation passing this value as M, callbackfn, thisArg as is, and true as updateKey.

1. A system without hoisting

An example of Scheme program without hoisting:

(define x 10)     ; global `x`
(print x)         ; 10

((lambda ()
    (print x)     ; still 10, not shadowed yet

	// by Dmitry Soshnikov <[email protected]>
	// MIT Style License.

	// Short URL for this example to run online is: http://cpp.sh/333

	#include <iostream>
	#include <vector>
	#include <ctype.h>
	#include <cstring>

	/**
	* "Is connected?"
	*
	* Dynamic connectivity issue.
	*
	* 1 2: not connected
	* 1--2: connected
	* 1--2--3: 1 and 3 are connected through 2
	*
	* by Dmitry Soshnikov <[email protected]>

	/**
	* "Is connected?"
	*
	* Dynamic connectivity issue.
	*
	* 1 2: not connected
	* 1--2: connected
	* 1--2--3: 1 and 3 are connected through 2
	*
	* This implements quick union operation, but the find

	/**
	* ES6 delegating generators.
	*
	* ES6 dramatically simplified calling of nested generators
	* using "yield *" construct, which is called delegating
	* generator.
	*
	* From history:
	* Previously (in the original SpiderMonkey/Python) implementation
	* we had to maintain a manual stack for it. The technique was

	/**
	* Educational Stack-based VM.
	*
	* See also:
	* - More complex example with recursion: https://gist.github.com/DmitrySoshnikov/afda459222e96e6002ac
	* - Register-based VM example: https://gist.github.com/DmitrySoshnikov/6407781
	*
	* by Dmitry Soshnikov <[email protected]>
	* http://dmitrysoshnikov.com
	* MIT Stye License (C) 2015

	/**
	* Educational Stack-based VM.
	*
	* See also:
	* - A simplified example without recursion: https://gist.github.com/DmitrySoshnikov/76e1cfb930df8d36145c
	* - Register-based VM example: https://gist.github.com/DmitrySoshnikov/6407781
	*
	* by Dmitry Soshnikov <[email protected]>
	* http://dmitrysoshnikov.com
	* MIT Stye License (C) 2015