The struct-id syntax class from syntax/parse/class/struct-id is puzzling
me. Given this preamble:
(require (for-syntax syntax/parse/class/struct-id
syntax/parse
syntax/parse/experimental/template
))
(struct person (name age height) #:transparent)
This works fine:
(define-syntax show-descript
(syntax-parser
[(_ id:struct-id) (template id.descriptor-id)]))
(show-descript person)
This is a compile-time error:
(define-syntax show-num-fields
(syntax-parser
[(_ id:struct-id) (template id.num-fields)]))
(show-num-fields person)
test.rkt:74:32: id.num-fields: attribute contains non-syntax value
value: 3
in: id.num-fields
context...:
/Applications/Racket_v6.11/collects/syntax/wrap-modbeg.rkt:46:4
standard-module-name-resolver
I've played around with various versions of 'attribute', 'datum->syntax',
and 'quasitemplate / untemplate' but been unable to sort it out. Can
someone explain it for me?
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