https://www.reddit.com/r/Racket/comments/ctcgam/i_made_a_pictorial_quine_in_pict_and_pict_pictcode/?utm_source=share&utm_medium=ios_app

It’s not official so I’d prefer not to use the racket name. It might be a possibility if it evolves into a successful way of introducing beginners and promoting racket.

I try to run this code from SICP book: (define (count-leaves x) (cond ((null? x) 0) ((not (pair? x)) 1) (else (+ (count-leaves (car x)) (count-leaves (cdr x)))))) (count-leaves '('(1 2) '(3 4))) 6 (count-leaves '((1 2) '(3 4))) 5 How can I explain the result

@thongpv87 The ' is turned into (quote ...) by the reader. So '(1 2) is short for (quote (1 2)). This means that the symbol quote is counted in the first example.

I thought the ' is the short cut to construct a list.

won’t it be turned into (list 1 2)?

or actually (quote (1 2))?

If I say “simon” you say simon.

The ’ or quote is the same concept for daturms.

A ’datum will produce a value that prints as datum.

so isn’t (1 2) the datum here?

Racket says (quote 1 2) is bad syntax

The concept is called quotation, but since (quote x) is cumbersome to write, you can abbreviate it as ’x.

(quote (1 2))

https://stackoverflow.com/questions/30150186/what-does-backtick-mean-in-lisp/30150276#30150276

yeah, you just said above: > So '(1 2) is short for (quote 1 2).

so I was briefly confused

Sorry - miswrote. Edited.

Quotation works with vectors and hashtables too.

is '(1 2) equivalent to (list 1 2)?

no

it’s equivalent to (quote (1 2))

although (list 1 2) seems to evaluate to the same thing

So quote is more abstract than list since it can construct vector and hashtable ?

It is does a different job. If you get some result printed in the repl, then you can copy paste the result into a program and put a ’ before it.

Thank you for the explanation.

Why this give me the result 3: (length (cons (list 1 2) (list 3 4)))

I thing the result should be 2.

cons isn’t append, so cons puts the entire (list 1 2) as the first element of a new list

so you get a list of (list 1 2), 3, and 4

so 3 items

Ah, I just forgot that. Thanks.