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What every architect should know about scripting languages

What is a scripting language

Dictionary definition

"A high-level programming language that is interpreted by another program at runtime rather than compiled by the computer's processor as other programming languages (such as C and C++) are."

Source: Webopedia

Common traits

  • Weak typing
  • Good reflection support
  • Meta programming
  • Strong at text processing
  • Closures

Examples

  • Perl
  • Python
  • Groovy
  • Ruby
  • ECMAScript (JavaScript/ActionScript)

Scripting languages are nothing new

  • Perl has long been a dominant language in all sizes of architecture
  • JavaScript/ActionScript now unavoidable in web applications

So why the recent hype?

  • Moore's law
  • More sophisticated
  • Rockstar developers

What can you do with scripting languages?

Rapid prototyping

  • Play with domain model without created lots of boiler plate

Glue code

  • User interfaces
  • Cron jobs
  • Maintenance scripts
  • Online debugging

ESB Configuration

class StringListTransformer {
  toList(src) {
    return src.toString().tokenize(",");
  }

  toString(src) {
    result="";
    src.each { t | result+= "," + t };
    return result.substring(1);
  }
}

Complex business logic

  • Zed Shaw - The ACL is dead 
    # 10 ACLs/Person/Container/Action
def rule_supervisor(person, action, role)
       person.departed &&
       allowed_actions.include?(action) &&
       role == :supervisor
end
  • All rules including bizarre corner cases applied with about 200 lines of Ruby

Testing

scenario "null is pushed onto empty stack", {
  given "an empty stack",{
    stack = new Stack()
  }

  when "null is pushed", {
    pushnull = {
      stack.push(null)
    }
  }

  then "an exception should be thrown", {
    ensureThrows(RuntimeException){
      pushnull()
    }
  }

  and "then the stack should still be empty", {
    stack.empty.shouldBe true
  }
}

Why use sciprting languages

Concise

  • Fewer lines of code
  • Less time spent
  • Less bugs (hopefully)
  • Easier to read
  • Business experts can verify correctness

Maintenance projects

  • Easily interact with existing infrastructure to produce quick wins
  • Perfect for adding CRUD interfaces to existing data sources

You have no choice

  • Almost all modern web applications involve scripting

But beware...

  • Probably too slow for performance critical components
  • Must be completely covered with automated tests