A domain specific language (DSL) is a great way of implementing systems focussed on particular areas. You can write everything in your favourite general-purpose language (be it Ruby Java or assembler language). But there are advantages to using a DSL.

A popular example. Cucumber uses a DSL called Gherkin to write its scenarios in for BDD testing. There are a number of advantages in using a DSL like Gherkin to program in rather than a general-purpose language. Firstly the code is much more readable, less obfuscated with special syntax. Secondly the DSL isolates the code from the next layer of software technology. In the case of Gherkin one could run the same scenarios not on a Ruby based Cucumber but on a Perl imitation. Lastly the DSL restricts what can be coded - it is as bad to have 10 ways of doing something as to have none.

In my hobby software development I’ve devised some homespun DSLs which I find useful. One is for scraping information off webpages. An example of this DSL:

every TD
attribute class Class
match Class "dataRowL"
text Date
next TD
text Description
next TD
text Amount
if
	match Amount "\D*(\d+.\d+)\D*" Value
	write Account Date Description Value ""
endif

This code snippet goes through every TD in a HTML page, check for those with class dataRowL, then gets a date, description, and amount from the following TD fields. If the amount is a number then it writes out the details.

These webpages also use a very simple DSL. For illustration here is this webpage as coded:

  @title		Domain Specific Languages
  @text
  A domain specific language (DSL) is a great way of
  implementing systems focussed on particular areas.  You
  can write everything in your favourite general-purpose
  language (be it *Ruby* *Java* or assembler
  language).  But there are advantages to using a DSL.

  A popular example.  [Cucumber](https://cucumber.io/) uses a DSL called
  Gherkin to write its scenarios in for BDD testing.
  There are a number of advantages in using a DSL like
  Gherkin to program in rather than a general-purpose
  language.  Firstly the code is much more readable, less
  obfuscated with special syntax.  Secondly the DSL isolates
  the code from the next layer of software technology.  In the
  case of Gherkin one could run the same scenarios not on
  a Ruby based Cucumber but on a Perl imitation.  Lastly
  the DSL restricts what can be coded - it is as bad to have
  10 ways of doing something as to have none.

  In my hobby software development I've devised some homespun
  DSLs which I find useful.  One is for scraping information
  off webpages.  An example of this 'DSL':

  @code
  every TD
  attribute class Class
  match Class "dataRowL"
  text Date
  next TD
  text Description
  next TD
  text Amount
  if
    match Amount "\D*(\d+.\d+)\D*" Value
    write Account Date Description Value ""
  endif

  @text
  This code snippet goes through every *TD* in a HTML
  page, check for those with class "*dataRowL*", then
  gets a date, description, and amount from the following
  *TD* fields.  If the amount is a number then it
  writes out the details.

  These webpages also use a very simple DSL.  For illustration
  here is this webpage as coded: