Question about AST formats in the Racket book section 1.2

[siadat]

Thanks for this great book. Just started reading the Racket book and I had a question regarding Section 1.2 (page 4). The AST examples are written in a format that is similar to the BNF grammar, and are not Racket code. Is that intentional?

For example, the AST for negative 8 is represented as this:

(Prim '- ((Int 8)))

The equivalent Racket code would be

(Prim '- (list (Int 8)))

I'm learning Racket at the same time, and I was wondering why we don't use Racket to represent the AST. Thanks!

[jsiek]

It looks like I forgot the single-quote in a bunch of places.
That is, in Racket,
'(1 2 3)
is another way to write
(list 1 2 3)
I'll look into fixing this when I get back from vacation.

[siadat]

Thanks! In the grammar, (exp) represents a list with one expression, which matches the ASTs. So, if we update the ASTs we might want to consider updating the grammar as well, perhaps to something like this:

exp ::= (Prim '- (list exp))

Just an observation regarding single-quote vs list: with single-quote the expressions inside the list get quoted as well and the result may be different, e.g. (list (+ 1 2) 3) != '((+ 1 2) 3).

I am excited to continue to follow the book this week. Enjoy your vacation! :)