| > I never wrote that macros are required to control evaluation. I think that came from me. My point was mainly that 1) control over evaluation is a significant reason to use macros 2) there are other ways to achieve that goal and 3) those other ways should be used to the extent possible. To me at least, this diminishes the value of one of the key headline features of the Lisp family of languages. Note that this does not mean that I don't want to use the language.'I've maintained a personal and professional interest in the language that dates back over 25 years. When I have the choice, I usually reach for Lisp (really Clojure these days) as the most effective way to write the software I have the time and interest to write. It's just that the reasons for this don't center around the idea of compile time code transformation. (As useful as that can be when needed.) > There are common examples of macros that use machine-generated unique variables to hold the results of evaluating an argument form, in order to be able to insert that value into multiple places in the generated code. An implementation of with-slots likely has to, for instance. I do know this, because I've written at least a few of them myself. https://github.com/mschaef/vcsh/blob/255afa60adf180e7e3e5b6e... https://github.com/mschaef/vcsh/blob/255afa60adf180e7e3e5b6e... Edit: > ... insert that value into multiple places in the generated code. Is that really what you meant to say? You're using a machine generated variable in a macro to 'insert a _value_ into multiple places in the generated code'? (As in, the value itself gets emitted in the generated code?) The code I link to above does something slightly different. What it does is generate code that uses a machine generated variable to hold the result of a single execution of an expression. It then inserts references to that machine generated unique variable in multiple places in the generated code. |