[adql]

Yes but library that turns a part of syntax of language into DSL to solve certain problem have advantage of developers already knowing that language, developers needing to learn only one language, and ability to use with that DSL anything else language libraries offer.

The problem is really "does the language app uses works for target audience that will be doing the DSL". If it does (Ruby makes pretty decent one), job done, if it doesn't, we end up in the mess of making toy languages (usually because developers want to do something fun and writing new small language can be pretty fun) or plugging something like Lua into it.