What is a scripting engine?

Question

I've seen here that what sets a programming language apart from a scripting language is the scripting engine. But I don't understand how it works, so I don't know the difference.

For example, I see code in Java calling methods in imported libraries, but it doesn't seem "different enough" from Python or Ruby code - both are scripting languages, right? I guess this also has to do with the procedural and object oriented paradigms, but in the end, I can't see why they are classified they way they are.

EDIT: About a scripting engine being an interpreter... Isn't Java an interpreted language? I know there's the compiled bytecode, but still, it doesn't make sense to me.

Answer 1

There is no hard and fast line between a "scripting language" and a "programming language".

Properties of "scripting languages" tend to include:

• garbage-collected memory manager, with no need to explicitly allocate and free objects

• ability to simply execute commands, without a bunch of boilerplate code. Java is usually used as a counter-example of this. In Python you can simply say print("Hello, world!") but in Java you need a lot more syntax (the example here is seven lines of code).

• Related to the above, usually in a "scripting language" you don't have to explicitly declare variables, and you rarely need to declare types of variables. Some scripting languages (such as Javascript) will coerce types with wild abandon, and others (such as Python) are strongly typed and raise exceptions on type mismatches.

• no need for an explicit compile or link step; you just write code and run it. (A "scripting language" can still be Just-In-Time compiled internally; Python does this, for example.)

Beyond these basics, a "scripting language" can range from something primitive and trivial, like the "batch" language in MS-DOS, on up to an expressive and powerful language like Python, Ruby, etc.

Answer 2

You've basically discovered that the distinction between a scripting language and a "non-scripting" language is pretty artificial. Python can be compiled to JVM bytecode (with Jython), and I believe Ruby also can -- then the "engine" running the Python or Ruby code in question will be a JVM, the same "engine" that runs Java code (or Scala code, etc etc). Similarly with .NET and IronPython (or IronRuby) -- then the "engine" is Microsoft's CLR, just as for C#, Boo, and so on. Languages said to be "scripting" are often dynamically typed ones... but I've never heard the term used for other important dynamically typed languages such as Smalltalk, Mozart/OZ, or Erlang...;-).