Curiosity: What does progn stands for?

Question

According to Emacs documentation:

progn is a special form in `C source code'.

(progn BODY...)

Eval BODY forms sequentially and return value of last one.

wasamasa · Accepted Answer · 2014-12-28 21:07:31Z

34

progn is a special form borrowed from CL-like Lisp dialects. In their implementations it's composed from multiple progs, expressions that are evaluated and a number that specifies which expression value is returned. prog1 for instance evaluates all expressions and returns the value of the first, prog2 evaluates all expressions and returns the value of the second, progn evaluates all expressions and returns the n'th, or rather, the last expression's value.
progn in Emacs Lisp is the equivalent of Clojure's do which is used as means to bundle multiple expressions into a single one. You'll need to use it for Clojure's if conditional for instance.

answered Dec 28, 2014 at 12:25

wasamasa

21.5k1 gold badge65 silver badges94 bronze badges

1

Good answer, I upvoted it. However, for the sake of formality: you don't really need it for conditionals, cond has an implicit progn.
– mbork
Dec 28, 2014 at 21:01
2

Uh, I was speaking of Clojure which does not have implicit progn in its if.
– wasamasa
Dec 28, 2014 at 21:04
3

Emacs also has prog1 and prog2 as built-in special forms.
– cjm
Dec 29, 2014 at 6:32
1

I have seen this used in a lot of users' configurations. Is there a performance boost from "bundling" multiple expressions this way as opposed to evaluating them one after the other outside of progn?
– elethan
Dec 3, 2015 at 3:41
Not sure what makes you think that. progn is the equivalent of a braced block in a C-like language...
– wasamasa
Dec 3, 2015 at 7:57

Add a comment |

1 Answer 1