3 ms·
I remember finding it pretty revelatory the first time I saw LET defined as a macro like (defmacro let (bindings &body body) `((lambda ,(mapcar #'fir
by kbp 8y ago
I remember finding it pretty revelatory the first time I saw LET defined as a macro like
(defmacro let (bindings &body body)
`((lambda ,(mapcar #'first bindings) ,@body)
,@(mapcar #'second bindings)))
Seeing it use MAPCAR like that just made something click for me for whatever reason.
- disconcision 8y agoTo add on, Racket in particular has some very slick syntax for writing these kinds of things: (define-syntax-rule (let ([id expr] ...) body ...) ((λ (id ...) body ...) expr ...))
- yomly 8y agoI definitely liked this about Racket but I did also find the elipses to be a bit magic to begin with...
- disconcision 8y agoAs with all things, the trick to chase the magic away is to implement them. I recently made a little term rewriting library using racket/match syntax but with the pattern/templates specifiable at runtime. Ellipses were a bit confusing to begin with but when you break list patterns down into cons pairs + a cons-like pattern binary combinator to represent ellipses, it started making sense. The unexpected thing for me was that I thought nested ellipses were going to be the tough part, but it turns out they actually just... work.