You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
44 lines
1.4 KiB
Racket
44 lines
1.4 KiB
Racket
#lang br
|
|
(require "struct.rkt" "line.rkt" "misc.rkt")
|
|
(provide b-goto b-gosub b-return b-for b-next)
|
|
|
|
(define (b-goto num-expr)
|
|
(raise (change-line-signal num-expr)))
|
|
|
|
(define return-stack empty)
|
|
|
|
(define (b-gosub num-expr)
|
|
(let/cc return-cc
|
|
(push! return-stack return-cc)
|
|
(b-goto num-expr)))
|
|
|
|
(define (b-return)
|
|
(unless (pair? return-stack)
|
|
(raise-line-error "return without gosub"))
|
|
(define top-return-k (pop! return-stack))
|
|
(top-return-k))
|
|
|
|
(define thunk-table (make-hasheq))
|
|
|
|
(define-macro-cases b-for
|
|
[(_ LOOP-ID START END) #'(b-for LOOP-ID START END 1)]
|
|
[(_ LOOP-ID START END STEP)
|
|
#'(b-let LOOP-ID (let/cc loop-cc
|
|
(hash-set! thunk-table
|
|
'LOOP-ID
|
|
(λ ()
|
|
(define next-val (+ LOOP-ID STEP))
|
|
(if (next-val . in-closed-interval? . START END)
|
|
(loop-cc next-val)
|
|
(hash-remove! thunk-table 'LOOP-ID))))
|
|
START))])
|
|
|
|
(define (in-closed-interval? x start end)
|
|
((if (< start end) <= >=) start x end))
|
|
|
|
(define-macro (b-next LOOP-ID)
|
|
#'(begin
|
|
(unless (hash-has-key? thunk-table 'LOOP-ID)
|
|
(raise-line-error "next without for"))
|
|
(define thunk (hash-ref thunk-table 'LOOP-ID))
|
|
(thunk))) |