;; -*- Mode: Irken -*-

;; unfortunately we need pretty much have to implement a byte-level stack
;;  because of the need for internal pointers etc.

;; having second thoughts now.  the spec says "the call frame may not exist as a byte sequence",
;;  so it sounds like in principle we can use real data structures.

;; so, considering that... what kinds of things are stored on the stack?
;;
;; * frames
;; * locals
;; * 32-bit push/pop vals
;; * 'call stubs' (which sounds like a continuation).

(require "lib/basis.scm")
(require "lib/codecs/hex.scm")

;; multiple senses of 'stack' here:
;; 'vstack': this is the value stack used within a frame/function
;; 'gstack': this is the stack of frames/save/continuations/etc.
;; XXX: consider 'mstack' ('machine stack') rather than 'gstack'.

;; 'dest-type/addr'.  at first glance, this looks like a copy of the
;;  addressing mode pair.  But it's not... it encodes the type info
;;  into 0..3, but ALSO includes some other values related to string
;;  'execution' contexts.  So... yeah, I'll have to put that back.

(typealias vstack {len=int val=(list int)})
(typealias frame {locals=(vector int) vstack=vstack})

(datatype gstack
  (:frame frame gstack)       ;; frame, next
  (:save mode int int gstack) ;; dest-mode, dest-val, pc, next
  (:nil)
  )

(define (make-vstack)
  {len=0 val=(list:nil)})

(define (vstack/push! vs v)
  (set! vs.val (list:cons v vs.val))
  (set! vs.len (+ 1 vs.len))
  )

(define (vstack/pop! vs)
  (match vs.val with
    (hd . tl) -> (begin
                   (set! vs.val tl)
                   (set! vs.len (- vs.len 1))
                   hd)
    () -> (raise (:VStackUnderflow))
    ))

(define (vstack/stkcopy! vs n)
  (let ((vals (take vs.val n)))
    (for-list val (reverse vals)
      (vstack/push! vs val))))

(define (make-frame locals vstack)
  {locals=locals vstack=vstack}
  )