# Trying to learn macros, have question on code snippet **URL:** \ **Category:** Questions & Answers\ **Created:** [January 4, 2022, 2:11pm UTC](https://racket.discourse.group/t/trying-to-learn-macros-have-question-on-code-snippet/523 "2022-01-04T14:11:03Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![maketo](https://avatars.discourse-cdn.com/v4/letter/m/a698b9/32.png) [@maketo](https://racket.discourse.group/u/maketo)\ **Post date:** [January 4, 2022, 2:11pm UTC](https://racket.discourse.group/t/trying-to-learn-macros-have-question-on-code-snippet/523/1 "2022-01-04T14:11:03Z")
Hello. I am new to Scheme/Racket (not to programming) and am trying to learn Racket through BeautifulRacket. After a few chapters I got interested in learning more about Racket's macro capabilities (before going back to the BR chapters) and ran off to read Greg Hendershott's "Fear of Macros". In it, in chapter 4 ([4 Pattern matching: syntax-case and syntax-rules](https://www.greghendershott.com/fear-of-macros/pattern-matching.html)), he has this code (the idea is to provide a capability to "index" into a hash table using dot notation, I guess - such as (hash.refs js.a.b.c) should return "value"): ```scheme (define js (hasheq 'a (hasheq 'b (hasheq 'c "value")))) (define/contract (hash-refs h ks [def #f]) ((hash? (listof any/c)) (any/c) . ->* . any) (with-handlers ([exn:fail? (const (cond [(procedure? def) (def)] [else def]))]) (for/fold ([h h]) ([k (in-list ks)]) (hash-ref h k)))) (define-syntax (hash.refs stx) (syntax-case stx () ; If the optional ‘default' is missing, use #f. [(_ chain) #'(hash.refs chain #f)] [(_ chain default) (let* ([chain-str (symbol->string (syntax->datum #'chain))] [ids (for/list ([str (in-list (regexp-split #rx"\." chain-str))]) (format-id #'chain "~a" str))]) (with-syntax ([hash-table (car ids)] [keys (cdr ids)]) #'(hash-refs hash-table 'keys default)))])) ``` What I am getting stuck on is -\> why is "keys" (a list) in #'(hash-refs hash-table 'keys default)))])) quoted? Thanks! ---
**Author:** ![soegaard](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/soegaard/32/19_2.png) [@soegaard](https://racket.discourse.group/u/soegaard)\ **Post date:** [January 4, 2022, 7:21pm UTC](https://racket.discourse.group/t/trying-to-learn-macros-have-question-on-code-snippet/523/2 "2022-01-04T19:21:17Z")
![image](https://global.discourse-cdn.com/free1/uploads/racket/original/1X/baf683f01d5a5e2e8137dcd914c9600b5544089e.png) In `(with-syntax ([keys (cdr ids)[) ...)` the pattern `keys` is bound to a syntax object representing a list (the result of `(cdr ids)`). Within the template that begins with `#'` the pattern variable `keys` will be replaced by the syntax object to which it is bound - that is, it will be replaced the the identifiers from `(cdr ids)`. ---
**Author:** ![benknoble](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/benknoble/32/16_2.png) [@benknoble](https://racket.discourse.group/u/benknoble)\ **Post date:** [January 4, 2022, 7:35pm UTC](https://racket.discourse.group/t/trying-to-learn-macros-have-question-on-code-snippet/523/3 "2022-01-04T19:35:06Z")
I think, IOW, that `keys` contains the equivalent of `#'(a b c)` (assuming the invocation was something like `(hash.refs table a b c)`). When putting this list in, without a quote, it would expand to `(hash-refs table (a b c) #f)`. This is unlikely to be correct; what we really want is `(hash.refs table '(a b c) #f)`. With `syntax-parse` this kind of example is a bit clearer, but Fear of Macros does a nice job connecting the dots between low-level macro primitives and higher-level DSLs like `syntax-case`/`syntax-parse`. ---
**Author:** ![maketo](https://avatars.discourse-cdn.com/v4/letter/m/a698b9/32.png) [@maketo](https://racket.discourse.group/u/maketo)\ **Post date:** [January 4, 2022, 7:45pm UTC](https://racket.discourse.group/t/trying-to-learn-macros-have-question-on-code-snippet/523/4 "2022-01-04T19:45:07Z")
> [@soegaard](#): > > In `(with-syntax ([keys (cdr ids)[) ...)` the pattern `keys` is bound to a syntax object representing a list (the result of `(cdr ids)` ). > > Within the template that begins with `#'` the pattern variable `keys` will be replaced by the syntax object to which it is bound - that is, it will be replaced the the identifiers from `(cdr ids)` . I guess what has/had me confused is that in the same code, one line above "hash-table" is the first element of "ids" and I guess that's a syntax object as well, yet it is not quoted in the #'(hash-refs hash-table 'keys default) line. I got a bit confused, new to this. Thanks 🙂 ---
**Author:** ![maketo](https://avatars.discourse-cdn.com/v4/letter/m/a698b9/32.png) [@maketo](https://racket.discourse.group/u/maketo)\ **Post date:** [January 4, 2022, 7:45pm UTC](https://racket.discourse.group/t/trying-to-learn-macros-have-question-on-code-snippet/523/5 "2022-01-04T19:45:44Z")
> [@benknoble](#): > > I think, IOW, that `keys` contains the equivalent of `#'(a b c)` (assuming the invocation was something like `(hash.refs table a b c)` ). When putting this list in, without a quote, it would expand to `(hash-refs table (a b c) #f)` . This is unlikely to be correct; what we really want is `(hash.refs table '(a b c) #f)` . Yep, that makes perfect sense to me. Thanks 🙂