In ruby a DSL is just ruby as well, although it perhaps ends up having to _look_ more like ruby than a Lisp DSL would. (Not sure, only vaguely familiar with lisp). But at any rate it's the same thing as far as "create within your codebase", no extra work of a lexer, parser, etc. This is a thing people do in ruby and call it a "DSL", when they are using fancy techniques to make it especially concisely expressed and well-fit for the domain (but it's still really just ruby under the hood, no parsing step but parsing ruby code with your ordinary ruby interpreter).

Which has always made me think... so HOW is this different than an API anyway, why does it have a special name? Aren't all API's "domain-specific languages" of a sort? Certainly they can be good or bad APIs, in a variety of ways, including being a good or poor fit for the domain of work they are trying to enable. But if in the end the implementation is just (ruby) calling methods on instances, or (lisp) calling macros and lambdas (or however you'd describe it in lisp if i've gotten it wrong)... isn't that what every API is, what's the difference?