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aoc-racket/2017/d5/main.rkt

26 lines
786 B
Racket

#lang sugar/debug br/quicklang
(require "../helper.rkt")
(provide read-syntax)
(define (read-syntax path port)
(strip-context #`(module mod "main.rkt"
#,@(for/list ([datum (in-port read port)])
datum))))
(provide (rename-out [#%mb #%module-begin]))
(define-macro (#%mb STARS JMP ...)
#'(#%module-begin (escape 'STARS (list->vector '(JMP ...)))))
(define (escape stars vec)
(let/ec exit
(for/fold ([pos 0])
([i (in-naturals)])
(unless (<= 0 pos (sub1 (vector-length vec)))
(exit i))
(define jmp (vector-ref vec pos))
(vector-set! vec pos (if (and (eq? stars '★★) (>= jmp 3))
(sub1 jmp)
(add1 jmp)))
(+ pos jmp))))