I've been programming with given(s) for a little while now, and I really like it. Can't say why I'm so vehement, but it's definitely a Good Thing™. Thank you for bringing this up again (and a "thank you" to aidenn0, if he/she is still reading these fora, for suggesting this in the first place).
An interesting bit about 'givens is that it makes functional programming in an imperative style almost seamless:
(givens f (car n)
v f!v
_ (prn v) ; v isn't being set properly in some cases for some reason...
l (combinatorics f v)
_ (prn l) ; debugprint
(is l 'undef))
The difference between given and let/with is that you cannot have more than one statement in the body of the given. For instance:
arc> (given (a b) (list 1 2)
(prn "Here")
(pr a b))
Error: "Can't understand fn arg list \"Here\""
What's happening here is that given is trying to bind (prn "Here") to (pr a b), but (naturally) can't bind a string; it takes the first n args, where n is the largest even number less than or equal to the number of arguments provided, and interprets them as variables. You must, therefore, write
arc> (given (a b) (list 1 2)
(do
(prn "Here")
(pr a b))
Here
121
.
Also, I highly recommend switching to Anarki. It's got bugfixes and enhancements galore (and even runs on the newest version of mzscheme).
It's the only "drawback", if such it is. I feel that since you need extra parentheses for either the body or the variables, it's better to wrap the body in a do, since that's less common.
