> Over the last couple years a way I've come to view software is that a sufficiently complex library, class, api, or even just file IS a DSL. Yes. A macro give

> Over the last couple years a way I've come to view software is that a sufficiently complex library, class, api, or even just file IS a DSL. Yes. A macro gives a certain programming feature a name and a syntax. But with a function we also need to give it a name and we need to define the arguments. In the case of function arguments, we also need to know what the input and output of those function needs to be. For example in Lisp there is a macro WITH-OPEN-FILE, which opens a file, executes code using the input stream and then closes the file. It also ensures that the file is also closed in case of an error. (with-open-file (stream filename) (read stream)) We now may have two other ways to deal with that often needed functionality: write the code or use a function which does the same (here in this example this is possible, but often a macro does something which a function can't). First we write the code. We may pull this from a snippet library. We have to remember what the primitives are and what they do. (let (stream return-value) (unwind-protect (setf return-value (progn (setf stream (open filename)) (read stream))) (close stream) return-value)) Or we write a function. This gets a name CALL-WITH-OPEN-FILE, a list of arguments and in case of the function it needs to now what the input and outputs are: a stream is the input and the result is arbitrary, but will be returned by CALL-WITH-OPEN-FILE. (call-with-open-file filename (lambda (stream) (read stream))) For the macro we need to know: * the name of the macro * the syntax of the macro: with-open-file (<symbol, non-evaluated> <filename, evaluated>) form* * what the generated code is supposed to do For the function we need to know: * the name of the function * the list of arguments and their order * the types and semantics of the arguments: a filename and a function which takes a stream * what the function is supposed to do The effect is basically the same: both ways are essential leading to a DSL, where the language operators and their usage has to be learned.