Add something like a garbage collector

Split heap into temporary "little heap" and permanent "big heap".
Defined symbols get copied into big heap, and little heap is
reset after each REPL iteration.

1 files changed, 55 insertions, 0 deletions

diff --git a/heap.s b/heap.s
new file mode 100644
index 0000000..00f47e2
--- /dev/null
+++ b/heap.s
@@ -0,0 +1,55 @@
+; copy s-exp into big (permanent) heap
+; R0 = arg1
+; big heap at 11000
+; touches R0, R1, R2
+copy:
+005400 032710 BIT #1, (R0)          ; test if cons or atom
+005402 000001
+005404 001016 BNE is_atom           ; branch if atom
+; otherwise it's cons:
+005406 011046 MOV @R0, -(SP)        ; save car to stack
+005410 016000 MOV 2(R0), R0         ; arg1 <- cdr
+005412 000002
+005414 004737 JSR PC, @copy         ; result <- copy(cdr)
+005416 005400
+005420 010001 MOV R0, R1            ; arg2 <- result
+005422 012600 MOV (SP)+, R0         ; arg1 <- car from stack
+005424 010146 MOV R1, -(SP)         ; save arg2
+005426 004737 JSR PC, @copy         ; arg1 <- copy(car)
+005430 005400
+005432 012601 MOV (SP)+, R1         ; restore arg2
+005434 004737 JSR PC, @big_cons     ; allocate cons cell
+005436 005600
+005440 000207 RTS PC
+is_atom:
+005442 013702 MOV @#11000, R2       ; get free pointer
+005444 011000
+005446 010246 MOV R2, -(SP)         ; save new atom start address
+005450 010201 MOV R2, R1
+005452 062701 ADD #3, R1
+005454 000003
+005456 010122 MOV R1, (R2)+         ; allocate atom tag and increment free pointer
+005460 011000 MOV @R0, R0
+005462 005300 DEC R0                ; get string address
+005464 112022 MOVB (R0)+, (R2)+     ; copy one byte
+005466 001376 BNE -4                ; if not null continue copying chars
+005470 005202 INC R2                ; align free pointer
+005472 042702 BIC #1, R2
+005574 000001
+005576 010237 MOV R2, @#11000       ; store new free pointer
+005500 011000
+005502 012600 MOV (SP)+, R0         ; result <- address of new atom
+005504 000207 RTS PC
+
+big_cons:
+005600 013702 MOV @#11000, R2       ; get free pointer
+005602 011000
+005604 010012 MOV R0, @R2           ; move arg1 to car of new cons cell
+005606 010162 MOV R1, 2(R2)         ; move arg2 to cdr of new cons cell
+005610 000002
+005612 010200 MOV R2, R0            ; result <- new cons cell
+005614 062702 ADD 4, R2             ; advance free pointer
+005616 000004
+005620 010237 MOV R2, @#11000       ; store new free pointer
+005622 011000
+005624 000207 RTS PC