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#lang racket | |
(require (for-syntax syntax/parse | |
syntax/parse/experimental/template | |
racket/syntax | |
racket/list)) | |
;; A syntax class to recognize function arguments: | |
(begin-for-syntax | |
(define-splicing-syntax-class argspec | |
#:description "argument" | |
#:attributes (id def kw) | |
(pattern id:id #:with kw #f #:with def #f) | |
(pattern [id:id def:expr] #:with kw #f) | |
(pattern (~seq kw:keyword id:id) #:with def #f) | |
(pattern (~seq kw:keyword [id:id def:expr])))) | |
(define-syntax (lam stx) | |
;; Parse into argspecs (e.g. "#:kw [n 0]" is one thing) | |
(syntax-parse stx | |
[(_ (arg:argspec ...) body ...+) | |
;; append* them down to decl format (e.g. #:kw [n 0] is again | |
;; multiple things), which we need for the lambda declaration. | |
(template | |
(lambda ((?@ . arg) ...) | |
body ...))])) | |
;; Use `lam' | |
(define f1 | |
(lam (x y) | |
(list x y))) | |
(f1 1 0) | |
;; => '(1 0) | |
;; Good. | |
;; Now a `define' variation: | |
(define-syntax (define-lam stx) | |
(syntax-parse stx | |
[(_ (name:id arg:expr ...) body ...+) | |
#'(define name (lam (arg ...) body ...))])) | |
;; Use `define-lam' | |
(define-lam (f2 x y) | |
(list x y)) | |
;; => x: unbound identifier in module | |
;; in: x | |
;; Huh? | |
(f2 1 0) |
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