Uses for Dynamic Languages

Question

My primary language right now is D, and I\'m in the process of learning Python because it\'s required for a course I\'m taking. While I understand why dynamic languages wou

Answer 1

Take a look at this e4x example in JavaScript:

var sales = 
    
    
    
  ;

alert( sales.item.(@type == "carrot").@quantity );
alert( sales.@vendor );
for each( var price in sales..@price ) {
  alert( price );
}

Especially, take a look at line:

alert( sales.item.(@type == "carrot").@quantity );

In typical static languages, you don’t get to write sales.item, since you can not know that item is property of sales until runtime. This is not limited to e4x. You get to program in similar style when connecting when writing SOAP clients or any other underlying type you do not know until runtime. In a static language, you would typically need to run a tool that will generate stub classes or program in a very verbose way. Then, if something changes in a web service, you need to regenerate stubs all over again. Take a look at java DOM code:

import org.dom4j.Document;
import org.dom4j.DocumentHelper;
import org.dom4j.Element;

public class Foo {

    public Document createDocument() {
        Document document = DocumentHelper.createDocument();
        Element root = document.addElement( "root" );

        Element author1 = root.addElement( "author" )
            .addAttribute( "name", "James" )
            .addAttribute( "location", "UK" )
            .addText( "James Strachan" );

        Element author2 = root.addElement( "author" )
            .addAttribute( "name", "Bob" )
            .addAttribute( "location", "US" )
            .addText( "Bob McWhirter" );

        return document;
    }
}

Definitely much more verbose than your dynamic code. And, of course, it is not statically typed. There is no way to check that you misspelled “author” as "autor" until runtime. All this verbosity is essentially there to let you capture something that is dynamic in nature in static style.

I think this is one of the strong points of dynamic languages.