2009/10/7 Joe Fredette
Let me add to this, as I've used the term "DSL" without (*gasp*) fully understanding it before.
In addition to "What is a DSL", I'd like to ask:
"How is a DSL different from an API?"
I don't think there is a sharp divide here. A nice example was given by Pat Hanrahan at the recent nvidia GPU conference. He proposed the idea that OpenGL was a DSL. His reasoning was that he could give a formal grammar that accurately captured the structure of many fragments of code making calls to OpenGL. For example you have blocks of code bracketed by glBegin() and glEnd() with sequences of primitives in between. In fact, some people indent their code to reflect this structure as if glBegin() and glEnd() were control structures within the host language. I've argued that every monad gives a DSL. They all have the same syntax - do-notation, but each choice of monad gives quite different semantics for this notation. For example the list monad gives a DSL for non-determinism. -- Dan