Or,
#lang racket
(require (for-syntax ) racket/stxparam)
(define-syntax-parameter return (syntax-rules ()))
(define-syntax-parameter false (syntax-rules ()))
(define-syntax fn
(syntax-rules ()
[(_ (arg ...) body ...)
(λ (arg ...)
(let/cc fn-exit
(syntax-parameterize ([return (syntax-rules () [(_ x) (fn-exit x)])])
(syntax-parameterize ([false (syntax-rules () [(_) (return #f)])])
body ...))))]))
((fn (x y) (when (< x y) (return x)) y) 2 30) ; => 2
((fn (x y) (when (< x y) (false)) y) 2 30) ;=> #f
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