mu/mu.arc

;; what happens when our virtual machine starts up
(= initialization-fns* (queue))
(def reset ()
  (each f (as cons initialization-fns*)
    (f)))

(mac on-init body
  `(enq (fn () ,@body)
        initialization-fns*))

;; persisting and checking traces for each test
(= traces* (queue))
(= trace-dir* ".traces/")
(ensure-dir trace-dir*)
(= curr-trace-file* nil)
(on-init
  (awhen curr-trace-file*
    (tofile (+ trace-dir* it)
      (each (label trace) (as cons traces*)
        (pr label ": " trace))))
  (= curr-trace-file* nil)
  (= traces* (queue)))

(def new-trace (filename)
  (prn "== @filename")
;?   )
  (= curr-trace-file* filename))

(= dump-trace* nil)
(def trace (label . args)
  (when (or (is dump-trace* t)
            (and dump-trace* (is label "-"))
            (and dump-trace* (pos label dump-trace*!whitelist))
            (and dump-trace* (no dump-trace*!whitelist) (~pos label dump-trace*!blacklist)))
    (apply prn label ": " args))
  (enq (list label (apply tostring:prn args))
       traces*))

(redef tr args  ; why am I still returning to prn when debugging? Will this help?
  (do1 nil
       (apply trace "-" args)))

(def tr2 (msg arg)
  (tr msg arg)
  arg)

(def check-trace-contents (msg expected-contents)
  (unless (trace-contents-match expected-contents)
    (prn "F - " msg)
    (prn "  trace contents")
    (print-trace-contents-mismatch expected-contents)))

(def trace-contents-match (expected-contents)
  (each (label msg) (as cons traces*)
    (when (and expected-contents
               (is label expected-contents.0.0)
               (posmatch expected-contents.0.1 msg))
      (pop expected-contents)))
  (no expected-contents))

(def print-trace-contents-mismatch (expected-contents)
  (each (label msg) (as cons traces*)
    (whenlet (expected-label expected-msg)  expected-contents.0
      (if (and (is label expected-label)
               (posmatch expected-msg msg))
        (do (pr "  * ")
            (pop expected-contents))
        (pr "    "))
      (pr label ": " msg)))
  (prn "  couldn't find")
  (each (expected-label expected-msg)  expected-contents
    (prn "  ! " expected-label ": " expected-msg)))

;; virtual machine state

; things that a future assembler will need separate memory for:
;   code; types; args channel
(def clear ()
  (= type* (table))
  (= memory* (table))
  (= function* (table))
  )
(enq clear initialization-fns*)

(on-init
  (= type* (obj
              ; Each type must be scalar or array, sum or product or primitive
              type (obj size 1)  ; implicitly scalar and primitive
              type-address (obj size 1  address t  elem '(type))
              type-array (obj array t  elem '(type))
              type-array-address (obj size 1  address t  elem '(type-array))
              location (obj size 1  address t  elem '(location))  ; assume it points to an atom
              integer (obj size 1)
              boolean (obj size 1)
              boolean-address (obj size 1  address t  elem '(boolean))
              byte (obj size 1)
              byte-address (obj  size 1  address t  elem '(byte))
              string (obj array t  elem '(byte))  ; inspired by Go
              ; an address contains the location of a specific type
              string-address (obj size 1  address t  elem '(string))
              string-address-address (obj size 1  address t  elem '(string-address))
              string-address-array (obj array t  elem '(string-address))
              string-address-array-address (obj size 1  address t  elem '(string-address-array))
              character (obj size 1)  ; int32 like a Go rune
              character-address (obj size 1  address t  elem '(character))
              ; isolating function calls
              scope (obj array t  elem '(location))  ; by convention index 0 points to outer scope
              scope-address (obj size 1  address t  elem '(scope))
              ; arrays consist of an integer length followed by that many
              ; elements, all of the same type
              integer-array (obj array t  elem '(integer))
              integer-array-address (obj size 1  address t  elem '(integer-array))
              integer-array-address-address (obj size 1  address t  elem '(integer-array-address))
              integer-address (obj size 1  address t  elem '(integer))  ; pointer to int
              integer-address-address (obj size 1  address t  elem '(integer-address))
              ; and-records consist of a multiple fields of different types
              integer-boolean-pair (obj size 2  and-record t  elems '((integer) (boolean))  fields '(int bool))
              integer-boolean-pair-address (obj size 1  address t  elem '(integer-boolean-pair))
              integer-boolean-pair-array (obj array t  elem '(integer-boolean-pair))
              integer-boolean-pair-array-address (obj size 1  address t  elem '(integer-boolean-pair-array))
              integer-integer-pair (obj size 2  and-record t  elems '((integer) (integer)))
              integer-point-pair (obj size 2  and-record t  elems '((integer) (integer-integer-pair)))
              integer-point-pair-address (obj size 1  address t  elem '(integer-point-pair))
              integer-point-pair-address-address (obj size 1  address t  elem '(integer-point-pair-address))
              ; tagged-values are the foundation of dynamic types
              tagged-value (obj size 2  and-record t  elems '((type) (location))  fields '(type payload))
              tagged-value-address (obj size 1  address t  elem '(tagged-value))
              tagged-value-array (obj array t  elem '(tagged-value))
              tagged-value-array-address (obj size 1  address t  elem '(tagged-value-array))
              tagged-value-array-address-address (obj size 1  address t  elem '(tagged-value-array-address))
              ; heterogeneous lists
              list (obj size 2  and-record t  elems '((tagged-value) (list-address))  fields '(car cdr))
              list-address (obj size 1  address t  elem '(list))
              list-address-address (obj size 1  address t  elem '(list-address))
              ; parallel routines use channels to synchronize
              channel (obj size 3  and-record t  elems '((integer) (integer) (tagged-value-array-address))  fields '(first-full first-free circular-buffer))
              ; be careful of accidental copies to channels
              channel-address (obj size 1  address t  elem '(channel))
              ; editor
              line (obj array t  elem '(character))
              line-address (obj size 1  address t  elem '(line))
              line-address-address (obj size 1  address t  elem '(line-address))
              screen (obj array t  elem '(line-address))
              screen-address (obj size 1  address t  elem '(screen))
              )))

;; managing concurrent routines

(on-init
  (= Memory-allocated-until 1000))

; routine = runtime state for a serial thread of execution
(def make-routine (fn-name . args)
  (do1
    (annotate 'routine (obj alloc Memory-allocated-until call-stack (list
        (obj fn-name fn-name  pc 0  args args  caller-arg-idx 0))))
    ; todo: allow routines to expand past initial allocation
    ; todo: do memory management in mu
    (++ Memory-allocated-until 1000)))

(defextend empty (x)  (isa x 'routine)
  (no rep.x!call-stack))

(def stack (routine)
  ((rep routine) 'call-stack))

(mac push-stack (routine op)
  `(push (obj fn-name ,op  pc 0  caller-arg-idx 0)
         ((rep ,routine) 'call-stack)))

(mac pop-stack (routine)
  `(pop ((rep ,routine) 'call-stack)))

(def top (routine)
  stack.routine.0)

(def body (routine (o idx 0))
  (function* stack.routine.idx!fn-name))

(mac pc (routine (o idx 0))  ; assignable
  `((((rep ,routine) 'call-stack) ,idx) 'pc))

(mac caller-arg-idx (routine (o idx 0))  ; assignable
  `((((rep ,routine) 'call-stack) ,idx) 'caller-arg-idx))

(mac caller-args (routine)  ; assignable
  `((((rep ,routine) 'call-stack) 0) 'args))
(mac caller-operands (routine)  ; assignable
  `((((rep ,routine) 'call-stack) 0) 'caller-operands))
(mac caller-results (routine)  ; assignable
  `((((rep ,routine) 'call-stack) 0) 'caller-results))

(mac results (routine)  ; assignable
  `((((rep ,routine) 'call-stack) 0) 'results))

(def waiting-for-exact-cycle? (routine)
  (is 'literal rep.routine!sleep.1))

(def ready-to-wake-up (routine)
  (assert no.routine*)
  (if (is 'literal rep.routine!sleep.1)
    (> curr-cycle* rep.routine!sleep.0)
    (~is rep.routine!sleep.1 (memory* rep.routine!sleep.0))))

(on-init
  (= running-routines* (queue))  ; simple round-robin scheduler
  ; set of sleeping routines; don't modify routines while they're in this table
  (= sleeping-routines* (table))
  (= completed-routines* nil)  ; audit trail
  (= routine* nil)
  (= abort-routine* (parameter nil))
  (= curr-cycle* 0)
  (= scheduling-interval* 500)
  (= scheduler-switch-table* nil)  ; hook into scheduler for tests
  )

; like arc's 'point' but you can also call ((abort-routine*)) in nested calls
(mac routine-mark body
  (w/uniq (g p)
    `(ccc (fn (,g)
            (parameterize abort-routine* (fn ((o ,p)) (,g ,p))
              ,@body)))))

(def run fn-names
  (freeze-functions)
  (= traces* (queue))
  (each it fn-names
    (enq make-routine.it running-routines*))
  (while (~empty running-routines*)
    (= routine* deq.running-routines*)
    (trace "schedule" top.routine*!fn-name)
    (routine-mark
      (run-for-time-slice scheduling-interval*))
    (update-scheduler-state)
;?     (tr "after run iter " running-routines*)
;?     (tr "after run iter " empty.running-routines*)
    ))

; prepare next iteration of round-robin scheduler
;
; state before: routine* running-routines* sleeping-routines*
; state after: running-routines* (with next routine to run at head) sleeping-routines*
;
; responsibilities:
;   add routine* to either running-routines* or sleeping-routines* or completed-routines*
;   wake up any necessary sleeping routines (which might be waiting for a
;     particular time or for a particular memory location to change)
;   detect deadlock: kill all sleeping routines when none can be woken
(def update-scheduler-state ()
;?   (trace "schedule" curr-cycle*)
  (when routine*
    (if
        rep.routine*!sleep
          (do (trace "schedule" "pushing " top.routine*!fn-name " to sleep queue")
              (set sleeping-routines*.routine*))
        (~empty routine*)
          (do (trace "schedule" "scheduling " top.routine*!fn-name " for further processing")
              (enq routine* running-routines*))
        :else
          (do (trace "schedule" "done with routine")
              (push routine* completed-routines*)))
    (= routine* nil))
;?   (tr 111)
  (each (routine _) canon.sleeping-routines*
    (when (ready-to-wake-up routine)
      (trace "schedule" "waking up " top.routine!fn-name)
      (wipe sleeping-routines*.routine)  ; do this before modifying routine
      (wipe rep.routine!sleep)
      (++ pc.routine)
      (enq routine running-routines*)))
;?   (tr 112)
  (when (empty running-routines*)
    (whenlet exact-sleeping-routines (keep waiting-for-exact-cycle? keys.sleeping-routines*)
      (let next-wakeup-cycle (apply min (map [rep._!sleep 0] exact-sleeping-routines))
        (= curr-cycle* (+ 1 next-wakeup-cycle))
        (trace "schedule" "skipping to cycle " curr-cycle*)
        (update-scheduler-state))))
;?   (tr 113)
  (detect-deadlock)
;?   (tr 114)
  )

(def detect-deadlock ()
  (when (and (empty running-routines*)
             (~empty sleeping-routines*)
             (~some 'literal (map (fn(_) rep._!sleep.1)
                                  keys.sleeping-routines*)))
    (each (routine _) sleeping-routines*
      (wipe sleeping-routines*.routine)
      (= rep.routine!error "deadlock detected")
      (push routine completed-routines*))))

(def die (msg)
  (tr "die: " msg)
  (= rep.routine*!error msg)
  (= rep.routine*!stack-trace rep.routine*!call-stack)
  (wipe rep.routine*!call-stack)
  (iflet abort-continuation (abort-routine*)
    (abort-continuation)))

;; running a single routine

; value of an arg or oarg, stripping away all metadata
; wish I could have this flag an error when arg is incorrectly formed
(mac v (operand)  ; for value
  `((,operand 0) 0))

; routines consist of instrs
; instrs consist of oargs, op and args
(def parse-instr (instr)
  (iflet delim (pos '<- instr)
    (list (cut instr 0 delim)  ; oargs
          (v (instr (+ delim 1)))  ; op
          (cut instr (+ delim 2)))  ; args
    (list nil (v car.instr) cdr.instr)))

(def metadata (operand)
  cdr.operand)

(def ty (operand)
  (cdr operand.0))

(def literal? (operand)
  (in ty.operand.0 'literal 'offset 'fn))

(def typeinfo (operand)
  (or (type* ty.operand.0)
      (err "unknown type @(tostring prn.operand)")))

; operand accessors
(def nondummy (operand)  ; precondition for helpers below
  (~is '_ operand))

; just for convenience, 'new' instruction sometimes takes a raw string and
; allocates just enough space to store it
(def not-raw-string (operand)
  (~isa operand 'string))

(def address? (operand)
  (or (is ty.operand.0 'location)
      typeinfo.operand!address))

($:require "charterm/main.rkt")
($:require graphics/graphics)
(= Viewport nil)

; run instructions from 'routine*' for 'time-slice'
(def run-for-time-slice (time-slice)
  (point return
    (for ninstrs 0 (< ninstrs time-slice) (++ ninstrs)
      (if (empty body.routine*) (err "@stack.routine*.0!fn-name not defined"))
      ; falling out of end of function = implicit reply
      (while (>= pc.routine* (len body.routine*))
        (pop-stack routine*)
        (if empty.routine* (return ninstrs))
        (++ pc.routine*))
      (++ curr-cycle*)
      (trace "run" "-- " int-canon.memory*)
      (trace "run" curr-cycle* " " top.routine*!fn-name " " pc.routine* ": " (body.routine* pc.routine*))
;?       (trace "run" routine*)
      (when (atom (body.routine* pc.routine*))  ; label
        (when (aand scheduler-switch-table*
                    (alref it (body.routine* pc.routine*)))
          (++ pc.routine*)
          (trace "run" "context-switch forced " abort-routine*)
          ((abort-routine*)))
        (++ pc.routine*)
        (continue))
      (let (oarg op arg)  (parse-instr (body.routine* pc.routine*))
        (let results
              (case op
                ; arithmetic
                add
                  (do (trace "add" (m arg.0) " " (m arg.1))
                  (+ (m arg.0) (m arg.1))
                  )
                subtract
                  (- (m arg.0) (m arg.1))
                multiply
                  (* (m arg.0) (m arg.1))
                divide
                  (/ (real (m arg.0)) (m arg.1))
                divide-with-remainder
                  (list (trunc:/ (m arg.0) (m arg.1))
                        (mod (m arg.0) (m arg.1)))

                ; boolean
                and
                  (and (m arg.0) (m arg.1))
                or
                  (or (m arg.0) (m arg.1))
                not
                  (not (m arg.0))

                ; comparison
                equal
                  (is (m arg.0) (m arg.1))
                not-equal
                  (do (trace "neq" (m arg.0) " " (m arg.1))
                  (~is (m arg.0) (m arg.1))
                  )
                less-than
                  (< (m arg.0) (m arg.1))
                greater-than
                  (> (m arg.0) (m arg.1))
                lesser-or-equal
                  (<= (m arg.0) (m arg.1))
                greater-or-equal
                  (>= (m arg.0) (m arg.1))

                ; control flow
                jump
                  (do (= pc.routine* (+ 1 pc.routine* (v arg.0)))
                      (trace "jump" "jumping to " pc.routine*)
                      (continue))
                jump-if
                  (let flag (m arg.0)
                    (trace "jump" "checking that " flag " is t")
                    (when (is t flag)
                      (= pc.routine* (+ 1 pc.routine* (v arg.1)))
                      (trace "jump" "jumping to " pc.routine*)
                      (continue)))
                jump-unless  ; convenient helper
                  (let flag (m arg.0)
                    (trace "jump" "checking that " flag " is not t")
                    (unless (is t flag)
                      (= pc.routine* (+ 1 pc.routine* (v arg.1)))
                      (trace "jump" "jumping to " pc.routine*)
                      (continue)))

                ; data management: scalars, arrays, and-records (structs)
                copy
                  (m arg.0)
                get
                  (with (operand  (canonize arg.0)
                         idx  (v arg.1))
                    (assert (iso '(offset) (ty arg.1)) "record index @arg.1 must have type 'offset'")
                    (assert (< -1 idx (len typeinfo.operand!elems)) "@idx is out of bounds of record @operand")
                    (m `((,(apply + v.operand
                                    (map (fn(x) (sizeof `((_ ,@x))))
                                         (firstn idx typeinfo.operand!elems)))
                          ,@typeinfo.operand!elems.idx)
                         (raw))))
                get-address
                  (with (operand  (canonize arg.0)
                         idx  (v arg.1))
                    (assert (iso '(offset) (ty arg.1)) "record index @arg.1 must have type 'offset'")
                    (assert (< -1 idx (len typeinfo.operand!elems)) "@idx is out of bounds of record @operand")
                    (apply + v.operand
                             (map (fn(x) (sizeof `((_ ,@x))))
                                  (firstn idx typeinfo.operand!elems))))
                index
                  (withs (operand  (canonize arg.0)
                          elemtype  typeinfo.operand!elem
                          idx  (m arg.1))
                    (unless (< -1 idx array-len.operand)
                      (die "@idx is out of bounds of array @operand"))
                    (m `((,(+ v.operand
                              1  ; for array size
                              (* idx (sizeof `((_ ,@elemtype)))))
                           ,@elemtype)
                         (raw))))
                index-address
                  (withs (operand  (canonize arg.0)
                          elemtype  typeinfo.operand!elem
                          idx  (m arg.1))
                    (unless (< -1 idx array-len.operand)
                      (die "@idx is out of bounds of array @operand"))
                    (+ v.operand
                       1  ; for array size
                       (* idx (sizeof `((_ ,@elemtype))))))
                new
                  (if (isa arg.0 'string)
                    ; special-case: allocate space for a literal string
                    (new-string arg.0)
                    (let type (v arg.0)
                      (assert (iso '(literal) (ty arg.0)) "new: second arg @arg.0 must be literal")
                      (if (no type*.type)  (err "no such type @type"))
                      ; todo: initialize memory. currently racket does it for us
                      (if type*.type!array
                        (new-array type (m arg.1))
                        (new-scalar type))))
                sizeof
                  (sizeof `((_ ,(m arg.0))))
                length
                  (let base arg.0
                    (if (or typeinfo.base!array address?.base)
                      array-len.base
                      -1))

                ; tagged-values require one primitive
                save-type
                  (annotate 'record `(,((ty arg.0) 0) ,(m arg.0)))

                ; multiprocessing
                run
                  (run (v arg.0))
                fork
                  ; args: fn globals-table args ...
                  (let routine  (apply make-routine (m arg.0) (map m (nthcdr 2 arg)))
                    (= rep.routine!globals (when (len> arg 1) (m arg.1)))
                    (enq routine running-routines*))
                assert
                  (unless (m arg.0)
                    (die (v arg.1)))
                sleep
                  (let operand arg.0
;?                     (tr "sleep " operand)
                    ; store sleep as either (<cycle number> literal) or (<location> <current value>)
                    (if (is ty.operand.0 'literal)
                      (let delay v.operand
                        (trace "run" "sleeping until " (+ curr-cycle* delay))
                        (= rep.routine*!sleep `(,(+ curr-cycle* delay) literal)))
                      (do
;?                         (tr "blocking on " operand " -> " (addr operand))
                        (= rep.routine*!sleep `(,addr.operand ,m.operand))))
                    ((abort-routine*)))

                ; text interaction
                clear-screen
                  (do1 nil ($.charterm-clear-screen))
                clear-line
                  (do1 nil ($.charterm-clear-line))
                cursor
                  (do1 nil ($.charterm-cursor (m arg.0) (m arg.1)))
                print-primitive
                  (do1 nil ((if ($.current-charterm) $.charterm-display pr) (m arg.0)))
                read-key
                  (and ($.charterm-byte-ready?) ($.charterm-read-key))
                bold-mode
                  (do1 nil ($.charterm-bold))
                non-bold-mode
                  (do1 nil ($.charterm-normal))
                console-on
                  (do1 nil (if (no ($.current-charterm)) ($.open-charterm)))
                console-off
                  (do1 nil (if ($.current-charterm) ($.close-charterm)))

                ; graphics
                graphics-on
                  (do1 nil
                    ($.open-graphics)
                    (= Viewport ($.open-viewport "practice" 300 300)))
                graphics-off
                  (do1 nil
                    ($.close-graphics)
                    (= Viewport nil))
                mouse-position
                  (aif ($.ready-mouse-click Viewport)
                    (let posn ($.mouse-click-posn it)
                      (list (annotate 'record (list ($.posn-x posn) ($.posn-y posn))) t))
                    (list nil nil))

                ; user-defined functions
                next-input
                  (let idx caller-arg-idx.routine*
                    (++ caller-arg-idx.routine*)
                    (trace "arg" arg " " idx " " caller-args.routine*)
                    (if (len> caller-args.routine* idx)
                      (list caller-args.routine*.idx t)
                      (list nil nil)))
                input
                  (do (assert (iso '(literal) (ty arg.0)))
                      (= caller-arg-idx.routine* (v arg.0))
                      (let idx caller-arg-idx.routine*
                        (++ caller-arg-idx.routine*)
                        (trace "arg" arg " " idx " " caller-args.routine*)
                        (if (len> caller-args.routine* idx)
                          (list caller-args.routine*.idx t)
                          (list nil nil))))
                ; type and otype won't always easily compile. be careful.
                type
                  (ty (caller-operands.routine* (v arg.0)))
                otype
                  (ty (caller-results.routine* (v arg.0)))
                prepare-reply
                  (prepare-reply arg)
                reply
                  (do (when arg
                        (prepare-reply arg))
                      (let results results.routine*
                        (pop-stack routine*)
                        (if empty.routine* (return ninstrs))
                        (let (caller-oargs _ _)  (parse-instr (body.routine* pc.routine*))
                          (trace "reply" arg " " caller-oargs)
                          (each (dest val)  (zip caller-oargs results)
                            (when nondummy.dest
                              (trace "reply" val " => " dest)
                              (setm dest val))))
                        (++ pc.routine*)
                        (while (>= pc.routine* (len body.routine*))
                          (pop-stack routine*)
                          (when empty.routine* (return ninstrs))
                          (++ pc.routine*))
                        (continue)))
                ; else try to call as a user-defined function
                  (do (if function*.op
                        (with (callee-args (accum yield
                                             (each a arg
                                               (yield (m a))))
                               callee-operands (accum yield
                                                 (each a arg
                                                   (yield a)))
                               callee-results (accum yield
                                                (each a oarg
                                                  (yield a))))
                          (push-stack routine* op)
                          (= caller-args.routine* callee-args)
                          (= caller-operands.routine* callee-operands)
                          (= caller-results.routine* callee-results))
                        (err "no such op @op"))
                      (continue))
                )
              ; opcode generated some 'results'
              ; copy to output args
              (if (acons results)
                (each (dest val) (zip oarg results)
                  (unless (is dest '_)
                    (trace "run" val " => " dest)
                    (setm dest val)))
                (when oarg  ; must be a list
                  (trace "run" results " => " oarg.0)
                  (setm oarg.0 results)))
              )
        (++ pc.routine*)))
    (return time-slice)))

(def prepare-reply (args)
  (= results.routine*
     (accum yield
       (each a args
         (yield (m a))))))

; helpers for memory access respecting
;   immediate addressing - 'literal' and 'offset'
;   direct addressing - default
;   indirect addressing - 'deref'
;   relative addressing - if routine* has 'default-scope'

(def m (loc)  ; read memory, respecting metadata
  (point return
    (when (literal? loc)
      (return v.loc))
    (when (is v.loc 'default-scope)
      (return rep.routine*!call-stack.0!default-scope))
    (trace "m" loc)
    (assert (isa v.loc 'int) "addresses must be numeric (problem in convert-names?) @loc")
    (with (n  sizeof.loc
           addr  addr.loc)
;?       (trace "m" "reading " n " locations starting at " addr)
      (if (is 1 n)
            memory*.addr
          :else
            (annotate 'record
                      (map memory* (addrs addr n)))))))

(def setm (loc val)  ; set memory, respecting metadata
  (point return
    (when (is v.loc 'default-scope)
      (assert (is 1 sizeof.loc) "can't store compounds in default-scope @loc")
      (= rep.routine*!call-stack.0!default-scope val)
      (return))
    (assert (isa v.loc 'int) "can't store to non-numeric address (problem in convert-names?)")
    (trace "setm" loc " <= " val)
    (with (n  (if (isa val 'record) (len rep.val) 1)
           addr  addr.loc
           typ  typeof.loc)
      (trace "setm" "size of " loc " is " n)
      (assert n "setm: can't compute type of @loc")
      (assert addr "setm: null pointer @loc")
      (if (is 1 n)
        (do (assert (~isa val 'record) "setm: record of size 1 @(tostring prn.val)")
            (trace "setm" loc ": setting " addr " to " val)
            (= memory*.addr val))
        (do (if type*.typ!array
              ; size check for arrays
              (when (~is n
                         (+ 1  ; array length
                            (* rep.val.0 (sizeof `((_ ,@type*.typ!elem))))))
                (die "writing invalid array @(tostring prn.val)"))
              ; size check for non-arrays
              (when (~is sizeof.loc n)
                (die "writing to incorrect size @(tostring prn.val) => @loc")))
            (let addrs (addrs addr n)
              (each (dest src) (zip addrs rep.val)
                (trace "setm" loc ": setting " dest " to " src)
                (= memory*.dest src))))))))

(def typeof (operand)
  (let loc absolutize.operand
    (while (pos '(deref) metadata.loc)
      (zap deref loc))
    ty.loc.0))

(def addr (operand)
  (v canonize.operand))

(def addrs (n sz)
  (accum yield
    (repeat sz
      (yield n)
      (++ n))))

(def canonize (operand)
  (ret operand
    (zap absolutize operand)
    (while (pos '(deref) metadata.operand)
      (zap deref operand))))

(def array-len (operand)
  (trace "array-len" operand)
  (zap canonize operand)
  (if typeinfo.operand!array
        (m `((,v.operand integer) ,@metadata.operand))
      :else
        (err "can't take len of non-array @operand")))

(def sizeof (x)
  (trace "sizeof" x)
  (assert acons.x)
  (zap canonize x)
  (point return
;?   (tr "sizeof: checking @x for array")
  (when typeinfo.x!array
;?     (tr "sizeof: @x is an array")
    (assert (~is '_ v.x) "sizeof: arrays require a specific variable")
    (return (+ 1 (* array-len.x (sizeof `((_ ,@typeinfo.x!elem)))))))
;?   (tr "sizeof: not an array")
  (when typeinfo.x!and-record
;?     (tr "sizeof: @x is an and-record")
    (return (sum idfn
                 (accum yield
                   (each elem typeinfo.x!elems
                     (yield (sizeof `((_ ,@elem)))))))))
;?   (tr "sizeof: @x is a primitive")
  (return typeinfo.x!size)))

(def absolutize (operand)
  (if (no routine*)
        operand
      (is '_ v.operand)
        operand
      (pos '(raw) metadata.operand)
        operand
      (is 'global space.operand)
        (aif rep.routine*!globals
          `((,(+ it 1 v.operand) ,@(cdr operand.0))
            ,@(rem [caris _ 'space] metadata.operand)
            (raw))
          (die "routine has no globals: @operand"))
      :else
        (iflet base rep.routine*!call-stack.0!default-scope
          (lookup-space (rem [caris _ 'space] operand)
                        base
                        space.operand)
          operand)))

(def lookup-space (operand base space)
  (if (is 0 space)
    ; base case
    (if (< v.operand memory*.base)
      `((,(+ base 1 v.operand) ,@(cdr operand.0))
        ,@metadata.operand
        (raw))
      (die "no room for var @operand in routine of size @memory*.base"))
    ; recursive case
    (lookup-space operand (memory* (+ base 1))  ; location 0 points to parent space
                  (- space 1))))

(def space (operand)
  (or (alref operand 'space)
      0))

(def deref (operand)
  (assert (pos '(deref) metadata.operand))
  (assert address?.operand)
  (cons `(,(memory* v.operand) ,@typeinfo.operand!elem)
        (drop-one '(deref) metadata.operand)))

(def drop-one (f x)
  (when acons.x  ; proper lists only
    (if (testify.f car.x)
      cdr.x
      (cons car.x (drop-one f cdr.x)))))

; memory allocation

(def new-scalar (type)
;?   (tr "new scalar: @type")
  (ret result rep.routine*!alloc
    (++ rep.routine*!alloc (sizeof `((_ ,type))))))

(def new-array (type size)
;?   (tr "new array: @type @size")
  (ret result rep.routine*!alloc
    (++ rep.routine*!alloc (+ 1 (* (sizeof `((_ ,@type*.type!elem))) size)))
    (= memory*.result size)))

(def new-string (literal-string)
;?   (tr "new string: @literal-string")
  (ret result rep.routine*!alloc
    (= (memory* rep.routine*!alloc) len.literal-string)
    (++ rep.routine*!alloc)
    (each c literal-string
      (= (memory* rep.routine*!alloc) c)
      (++ rep.routine*!alloc))))

;; desugar structured assembly based on blocks

(def convert-braces (instrs)
;?   (prn "convert-braces " instrs)
  (let locs ()  ; list of information on each brace: (open/close pc)
    (let pc 0
      (loop (instrs instrs)
        (each instr instrs
;?           (tr instr)
          (if (or atom.instr (~is 'begin instr.0))  ; label or regular instruction
                (do
                  (trace "c{0" pc " " instr " -- " locs)
                  (++ pc))
                ; hack: racket replaces braces with parens, so we need the
                ; keyword 'begin' to delimit blocks.
                ; ultimately there'll be no nesting and braces will just be
                ; in an instr by themselves.
              :else  ; brace
                (do
                  (push `(open ,pc) locs)
                  (recur cdr.instr)
                  (push `(close ,pc) locs))))))
    (zap rev locs)
;?     (tr "-")
    (with (pc  0
           stack  ())  ; elems are pcs
      (accum yield
        (loop (instrs instrs)
          (each instr instrs
;?             (tr "- " instr)
            (point continue
            (when (atom instr)  ; label
              (yield instr)
              (++ pc)
              (continue))
            (when (is car.instr 'begin)
              (push pc stack)
              (recur cdr.instr)
              (pop stack)
              (continue))
            (let (oarg op arg)  (parse-instr instr)
              (trace "c{1" pc " " op " " oarg)
              (case op
                break
                  (do
                    (assert (is oarg nil) "break: can't take oarg in @instr")
                    (yield `(((jump)) ((,(close-offset pc locs (and arg (v arg.0))) offset)))))
                break-if
                  (do
                    (assert (is oarg nil) "break-if: can't take oarg in @instr")
                    (yield `(((jump-if)) ,arg.0 ((,(close-offset pc locs (and cdr.arg (v arg.1))) offset)))))
                break-unless
                  (do
                    (assert (is oarg nil) "break-unless: can't take oarg in @instr")
                    (yield `(((jump-unless)) ,arg.0 ((,(close-offset pc locs (and cdr.arg (v arg.1))) offset)))))
                loop
                  (do
                    (assert (is oarg nil) "loop: can't take oarg in @instr")
                    (yield `(((jump)) ((,(open-offset pc stack (and arg (v arg.0))) offset)))))
                loop-if
                  (do
                    (trace "cvt0" "loop-if: " instr " => " (- stack.0 1))
                    (assert (is oarg nil) "loop-if: can't take oarg in @instr")
                    (yield `(((jump-if)) ,arg.0 ((,(open-offset pc stack (and cdr.arg (v arg.1))) offset)))))
                loop-unless
                  (do
                    (trace "cvt0" "loop-if: " instr " => " (- stack.0 1))
                    (assert (is oarg nil) "loop-unless: can't take oarg in @instr")
                    (yield `(((jump-unless)) ,arg.0 ((,(open-offset pc stack (and cdr.arg (v arg.1))) offset)))))
                ;else
                  (yield instr)))
            (++ pc))))))))

(def close-offset (pc locs nblocks)
  (or= nblocks 1)
;?   (tr nblocks)
  (point return
;?   (tr "close " pc " " locs)
  (let stacksize 0
    (each (state loc) locs
      (point continue
;?       (tr stacksize "/" done " " state " " loc)
      (when (<= loc pc)
        (continue))
;?       (tr "process " stacksize loc)
      (if (is 'open state) (++ stacksize) (-- stacksize))
      ; last time
;?       (tr "process2 " stacksize loc)
      (when (is stacksize (* -1 nblocks))
;?         (tr "close now " loc)
        (return (- loc pc 1))))))))

(def open-offset (pc stack nblocks)
  (or= nblocks 1)
  (- (stack (- nblocks 1)) 1 pc))

;; convert jump targets to offsets

(def convert-labels (instrs)
;?   (tr "convert-labels " instrs)
  (let labels (table)
    (let pc 0
      (each instr instrs
        (when (~acons instr)
;?           (tr "label " pc)
          (= labels.instr pc))
        (++ pc)))
    (let pc 0
      (each instr instrs
        (when (and acons.instr
                   (acons car.instr)
                   (in (v car.instr) 'jump 'jump-if 'jump-unless))
          (each arg cdr.instr
;?             (tr "trying " arg " " ty.arg ": " v.arg " => " (labels v.arg))
            (when (and (is ty.arg.0 'offset)
                       (isa v.arg 'sym)
                       (labels v.arg))
              (= v.arg (- (labels v.arg) pc 1)))))
        (++ pc))))
  instrs)

;; convert symbolic names to raw memory locations

(def convert-names (instrs)
;?   (tr "convert-names " instrs)
  (with (location  (table)
         isa-field  (table))
    (let idx 1
      (each instr instrs
        (point continue
        (when atom.instr
          (continue))
        (trace "cn0" instr " " canon.location " " canon.isa-field)
        (let (oargs op args)  (parse-instr instr)
;?           (tr "about to rename args")
          ; rename args
          (if (in op 'get 'get-address)
            (with (basetype  (typeof args.0)
                   field  (v args.1))
              (assert type*.basetype!and-record "get on non-record @args.0")
              (trace "cn0" "field-access @field in @args.0 of type @basetype")
              (when (isa field 'sym)
                (assert (or (~location field) isa-field.field) "field @args.1 is also a variable")
                (when (~location field)
                  (trace "cn0" "new field; computing location")
;?                   (tr "aa " type*.basetype)
                  (assert type*.basetype!fields "no field names available for @instr")
;?                   (tr "bb")
                  (iflet idx (pos field type*.basetype!fields)
                    (do (set isa-field.field)
                        (trace "cn0" "field location @idx")
                        (= location.field idx))
                    (assert nil "couldn't find field in @instr")))))
            (each arg args
              (when (and nondummy.arg not-raw-string.arg)
                (assert (~isa-field v.arg) "arg @arg is also a field name")
                (when (maybe-add arg location idx)
                  (err "use before set: @arg")))))
;?           (tr "about to rename oargs")
          ; rename oargs
          (each arg oargs
            (trace "cn0" "checking " arg)
            (when (and nondummy.arg not-raw-string.arg)
              (assert (~isa-field v.arg) "oarg @arg is also a field name")
              (when (maybe-add arg location idx)
                (trace "cn0" "location for arg " arg ": " idx)
                ; todo: can't allocate arrays on the stack
                (++ idx (sizeof `((_ ,@ty.arg)))))))))))
    (trace "cn1" "update names " canon.location " " canon.isa-field)
    (each instr instrs
      (when (acons instr)
        (let (oargs op args)  (parse-instr instr)
          (each arg args
            (when (and nondummy.arg not-raw-string.arg (location v.arg))
              (zap location v.arg)))
          (each arg oargs
            (when (and nondummy.arg not-raw-string.arg (location v.arg))
              (zap location v.arg))))))
    instrs))

(def maybe-add (arg location idx)
  (trace "maybe-add" arg)
  (when (and nondummy.arg
             (~literal? arg)
             (~location v.arg)
             (isa v.arg 'sym)
             (~in v.arg 'nil 'default-scope)
             (~pos '(raw) metadata.arg))
    (= (location v.arg) idx)))

;; literate tangling system for reordering code

(def convert-quotes (instrs)
  (let deferred (queue)
    (each instr instrs
      (when (acons instr)
        (case instr.0
          defer
            (let (q qinstrs)  instr.1
              (assert (is 'make-br-fn q) "defer: first arg must be [quoted]")
              (each qinstr qinstrs
                (enq qinstr deferred))))))
    (accum yield
      (each instr instrs
        (if atom.instr  ; label
              (yield instr)
            (is instr.0 'defer)
              nil  ; skip
            (is instr.0 'reply)
              (do
                (when cdr.instr  ; return values
                  (= instr.0 'prepare-reply)
                  (yield instr))
                (each instr (as cons deferred)
                  (yield instr))
                (yield '(reply)))
            :else
              (yield instr)))
      (each instr (as cons deferred)
        (yield instr)))))

(on-init
  (= before* (table))  ; label -> queue of fragments
  (= after* (table)))  ; label -> list of fragments

; see add-code below for adding to before* and after*

(def insert-code (instrs (o name))
;?   (tr "insert-code " instrs)
  (loop (instrs instrs)
    (accum yield
      (each instr instrs
        (if (and (acons instr) (~is 'begin car.instr))
              ; simple instruction
              (yield instr)
            (and (acons instr) (is 'begin car.instr))
              ; block
              (yield `{begin ,@(recur cdr.instr)})
            (atom instr)
              ; label
              (do
;?                 (prn "tangling " instr)
                (each fragment (as cons (or (and name (before* (sym:string name '/ instr)))
                                            before*.instr))
                  (each instr fragment
                    (yield instr)))
                (yield instr)
                (each fragment (or (and name (after* (sym:string name '/ instr)))
                                   after*.instr)
                  (each instr fragment
                    (yield instr)))))))))

;; loading code into the virtual machine

(def add-code (forms)
  (each (op . rest)  forms
    (case op
      ; function <name> [ <instructions> ]
      ; don't apply our lightweight tools just yet
      function!
        (let (name (_make-br-fn body))  rest
          (assert (is 'make-br-fn _make-br-fn))
          (= function*.name body))
      function
        (let (name (_make-br-fn body))  rest
          (assert (is 'make-br-fn _make-br-fn))
          (= function*.name (join body function*.name)))

      ; and-record <type> [ <name:types> ]
      and-record
        (let (name (_make-br-fn fields))  rest
          (assert (is 'make-br-fn _make-br-fn))
          (let fields (map tokenize-arg fields)
            (= type*.name (obj size len.fields
                               and-record t
                               ; dump all metadata for now except field name and type
                               elems (map cdar fields)
                               fields (map caar fields)))))

      ; before <label> [ <instructions> ]
      ;
      ; multiple before directives => code in order
      before
        (let (label (_make-br-fn fragment))  rest
          (assert (is 'make-br-fn _make-br-fn))
          (or= before*.label (queue))
          (enq fragment before*.label))

      ; after <label> [ <instructions> ]
      ;
      ; multiple after directives => code in *reverse* order
      ; (if initialization order in a function is A B, corresponding
      ; finalization order should be B A)
      after
        (let (label (_make-br-fn fragment))  rest
          (assert (is 'make-br-fn _make-br-fn))
          (push fragment after*.label))
      )))

(def freeze-functions ()
;?   (prn "freeze")
  (each (name body)  canon.function*
;?     (tr name)
;?     (prn keys.before* " -- " keys.after*)
;?     (= function*.name (convert-names:convert-labels:convert-braces:prn:insert-code body)))
    (= function*.name (convert-names:convert-labels:convert-braces:tokenize-args:insert-code body name))))

(def tokenize-arg (arg)
;?   (tr "tokenize-arg " arg)
  (if (in arg '<- '_)
        arg
      (isa arg 'sym)
        (map [map [fromstring _ (read)] _]
             (map [tokens _ #\:]
                  (tokens string.arg #\/)))
      :else
        arg))

(def tokenize-args (instrs)
;?   (tr "tokenize-args " instrs)
;?   (prn2 "@(tostring prn.instrs) => "
  (accum yield
    (each instr instrs
      (if atom.instr
            (yield instr)
          (is 'begin instr.0)
            (yield `{begin ,@(tokenize-args cdr.instr)})
          :else
            (yield (map tokenize-arg instr))))))
;?   )

(def prn2 (msg . args)
  (pr msg)
  (apply prn args))

(def canon (table)
  (sort (compare < [tostring (prn:car _)]) (as cons table)))

(def int-canon (table)
  (sort (compare < car) (as cons table)))

;; test helpers

(def memory-contains (addr value)
;?   (prn "Looking for @value starting at @addr")
  (loop (addr addr
         idx  0)
;?     (prn "@idx vs @addr")
    (if (>= idx len.value)
          t
        (~is memory*.addr value.idx)
          (do1 nil
               (prn "@addr should contain @value.idx but contains @memory*.addr"))
        :else
          (recur (+ addr 1) (+ idx 1)))))

(def memory-contains-array (addr value)
;?   (prn "Looking for @value starting at @addr, size @memory*.addr vs @len.value")
  (and (>= memory*.addr len.value)
       (loop (addr (+ addr 1)
              idx  0)
;?          (prn "comparing @memory*.addr and @value.idx")
         (if (>= idx len.value)
               t
             (~is memory*.addr value.idx)
               (do1 nil
                    (prn "@addr should contain @value.idx but contains @memory*.addr"))
             :else
               (recur (+ addr 1) (+ idx 1))))))

;; system software
; create once, load before every test

(reset)
(= system-function* (table))

(mac init-fn (name . body)
  `(= (system-function* ',name) 
      (convert-names:convert-labels:convert-braces:tokenize-args:insert-code ',body ',name)))

(on-init
  (each (name f) system-function*
    (= (function* name)
       (system-function* name))))

(section 100

(init-fn maybe-coerce
  (default-scope:scope-address <- new scope:literal 30:literal)
  (x:tagged-value-address <- new tagged-value:literal)
  (x:tagged-value-address/deref <- next-input)
  (p:type <- next-input)
  (xtype:type <- get x:tagged-value-address/deref 0:offset)
  (match?:boolean <- equal xtype:type p:type)
  { begin
    (break-if match?:boolean)
    (reply 0:literal nil:literal)
  }
  (xvalue:location <- get x:tagged-value-address/deref 1:offset)
  (reply xvalue:location match?:boolean))

(init-fn init-tagged-value
  (default-scope:scope-address <- new scope:literal 30:literal)
  ; assert sizeof:arg.0 == 1
  (xtype:type <- next-input)
  (xtypesize:integer <- sizeof xtype:type)
  (xcheck:boolean <- equal xtypesize:integer 1:literal)
  (assert xcheck:boolean)
  ; todo: check that arg 0 matches the type? or is that for the future typechecker?
  (result:tagged-value-address <- new tagged-value:literal)
  ; result->type = arg 0
  (resulttype:location <- get-address result:tagged-value-address/deref type:offset)
  (resulttype:location/deref <- copy xtype:type)
  ; result->payload = arg 1
  (locaddr:location <- get-address result:tagged-value-address/deref payload:offset)
  (locaddr:location/deref <- next-input)
  (reply result:tagged-value-address))

(init-fn list-next  ; list-address -> list-address
  (default-scope:scope-address <- new scope:literal 30:literal)
  (base:list-address <- next-input)
  (result:list-address <- get base:list-address/deref cdr:offset)
  (reply result:list-address))

(init-fn list-value-address  ; list-address -> tagged-value-address
  (default-scope:scope-address <- new scope:literal 30:literal)
  (base:list-address <- next-input)
  (result:tagged-value-address <- get-address base:list-address/deref car:offset)
  (reply result:tagged-value-address))

(init-fn init-list
  (default-scope:scope-address <- new scope:literal 30:literal)
  ; new-list = curr = new list
  (result:list-address <- new list:literal)
  (curr:list-address <- copy result:list-address)
  { begin
    ; while read curr-value
    (curr-value:integer exists?:boolean <- next-input)
    (break-unless exists?:boolean)
    ; curr.cdr = new list
    (next:list-address-address <- get-address curr:list-address/deref cdr:offset)
    (next:list-address-address/deref <- new list:literal)
    ; curr = curr.cdr
    (curr:list-address <- list-next curr:list-address)
    ; curr.car = type:curr-value
    (dest:tagged-value-address <- list-value-address curr:list-address)
    (dest:tagged-value-address/deref <- save-type curr-value:integer)
    (loop)
  }
  ; return new-list.cdr
  (result:list-address <- list-next result:list-address)  ; memory leak
  (reply result:list-address))

(init-fn init-channel
  (default-scope:scope-address <- new scope:literal 30:literal)
  ; result = new channel
  (result:channel-address <- new channel:literal)
  ; result.first-full = 0
  (full:integer-address <- get-address result:channel-address/deref first-full:offset)
  (full:integer-address/deref <- copy 0:literal)
  ; result.first-free = 0
  (free:integer-address <- get-address result:channel-address/deref first-free:offset)
  (free:integer-address/deref <- copy 0:literal)
  ; result.circular-buffer = new tagged-value[arg+1]
  (capacity:integer <- next-input)
  (capacity:integer <- add capacity:integer 1:literal)  ; unused slot for full? below
  (channel-buffer-address:tagged-value-array-address-address <- get-address result:channel-address/deref circular-buffer:offset)
  (channel-buffer-address:tagged-value-array-address-address/deref <- new tagged-value-array:literal capacity:integer)
  (reply result:channel-address))

(init-fn capacity
  (default-scope:scope-address <- new scope:literal 30:literal)
  (chan:channel <- next-input)
  (q:tagged-value-array-address <- get chan:channel circular-buffer:offset)
  (qlen:integer <- length q:tagged-value-array-address/deref)
  (reply qlen:integer))

(init-fn write
  (default-scope:scope-address <- new scope:literal 30:literal)
  (chan:channel-address <- next-input)
  (val:tagged-value <- next-input)
  { begin
    ; block if chan is full
    (full:boolean <- full? chan:channel-address/deref)
    (break-unless full:boolean)
    (full-address:integer-address <- get-address chan:channel-address/deref first-full:offset)
    (sleep full-address:integer-address/deref)
  }
  ; store val
  (q:tagged-value-array-address <- get chan:channel-address/deref circular-buffer:offset)
  (free:integer-address <- get-address chan:channel-address/deref first-free:offset)
  (dest:tagged-value-address <- index-address q:tagged-value-array-address/deref free:integer-address/deref)
  (dest:tagged-value-address/deref <- copy val:tagged-value)
  ; increment free
  (free:integer-address/deref <- add free:integer-address/deref 1:literal)
  { begin
    ; wrap free around to 0 if necessary
    (qlen:integer <- length q:tagged-value-array-address/deref)
    (remaining?:boolean <- less-than free:integer-address/deref qlen:integer)
    (break-if remaining?:boolean)
    (free:integer-address/deref <- copy 0:literal)
  }
  (reply chan:channel-address/deref))

(init-fn read
  (default-scope:scope-address <- new scope:literal 30:literal)
  (chan:channel-address <- next-input)
  { begin
    ; block if chan is empty
    (empty:boolean <- empty? chan:channel-address/deref)
    (break-unless empty:boolean)
    (free-address:integer-address <- get-address chan:channel-address/deref first-free:offset)
    (sleep free-address:integer-address/deref)
  }
  ; read result
  (full:integer-address <- get-address chan:channel-address/deref first-full:offset)
  (q:tagged-value-array-address <- get chan:channel-address/deref circular-buffer:offset)
  (result:tagged-value <- index q:tagged-value-array-address/deref full:integer-address/deref)
  ; increment full
  (full:integer-address/deref <- add full:integer-address/deref 1:literal)
  { begin
    ; wrap full around to 0 if necessary
    (qlen:integer <- length q:tagged-value-array-address/deref)
    (remaining?:boolean <- less-than full:integer-address/deref qlen:integer)
    (break-if remaining?:boolean)
    (full:integer-address/deref <- copy 0:literal)
  }
  (reply result:tagged-value chan:channel-address/deref))

; An empty channel has first-empty and first-full both at the same value.
(init-fn empty?
  (default-scope:scope-address <- new scope:literal 30:literal)
  ; return arg.first-full == arg.first-free
  (chan:channel <- next-input)
  (full:integer <- get chan:channel first-full:offset)
  (free:integer <- get chan:channel first-free:offset)
  (result:boolean <- equal full:integer free:integer)
  (reply result:boolean))

; A full channel has first-empty just before first-full, wasting one slot.
; (Other alternatives: https://en.wikipedia.org/wiki/Circular_buffer#Full_.2F_Empty_Buffer_Distinction)
(init-fn full?
  (default-scope:scope-address <- new scope:literal 30:literal)
  (chan:channel <- next-input)
  ; curr = chan.first-free + 1
  (curr:integer <- get chan:channel first-free:offset)
  (curr:integer <- add curr:integer 1:literal)
  { begin
    ; if (curr == chan.capacity) curr = 0
    (qlen:integer <- capacity chan:channel)
    (remaining?:boolean <- less-than curr:integer qlen:integer)
    (break-if remaining?:boolean)
    (curr:integer <- copy 0:literal)
  }
  ; return chan.first-full == curr
  (full:integer <- get chan:channel first-full:offset)
  (result:boolean <- equal full:integer curr:integer)
  (reply result:boolean))

(init-fn strcat
  (default-scope:scope-address <- new scope:literal 30:literal)
  ; result = new string[a.length + b.length]
  (a:string-address <- next-input)
  (a-len:integer <- length a:string-address/deref)
  (b:string-address <- next-input)
  (b-len:integer <- length b:string-address/deref)
  (result-len:integer <- add a-len:integer b-len:integer)
  (result:string-address <- new string:literal result-len:integer)
  ; copy a into result
  (result-idx:integer <- copy 0:literal)
  (i:integer <- copy 0:literal)
  { begin
    ; while (i < a.length)
    (a-done?:boolean <- less-than i:integer a-len:integer)
    (break-unless a-done?:boolean)
    ; result[result-idx] = a[i]
    (out:byte-address <- index-address result:string-address/deref result-idx:integer)
    (in:byte <- index a:string-address/deref i:integer)
    (out:byte-address/deref <- copy in:byte)
    ; ++i
    (i:integer <- add i:integer 1:literal)
    ; ++result-idx
    (result-idx:integer <- add result-idx:integer 1:literal)
    (loop)
  }
  ; copy b into result
  (i:integer <- copy 0:literal)
  { begin
    ; while (i < b.length)
    (b-done?:boolean <- less-than i:integer b-len:integer)
    (break-unless b-done?:boolean)
    ; result[result-idx] = a[i]
    (out:byte-address <- index-address result:string-address/deref result-idx:integer)
    (in:byte <- index b:string-address/deref i:integer)
    (out:byte-address/deref <- copy in:byte)
    ; ++i
    (i:integer <- add i:integer 1:literal)
    ; ++result-idx
    (result-idx:integer <- add result-idx:integer 1:literal)
    (loop)
  }
  (reply result:string-address))

; replace underscores in first with remaining args
(init-fn interpolate  ; string-address template, string-address a..
  (default-scope:scope-address <- new scope:literal 60:literal)
  (template:string-address <- next-input)
  ; compute result-len, space to allocate for result
  (tem-len:integer <- length template:string-address/deref)
  (result-len:integer <- copy tem-len:integer)
  { begin
    ; while arg received
    (a:string-address arg-received?:boolean <- next-input)
    (break-unless arg-received?:boolean)
;?     (print-primitive ("arg now: " literal))
;?     (print-primitive a:string-address)
;?     (print-primitive "@":literal)
;?     print-primitive:a:string-address/deref  ; todo: test (m on scoped array)
;?     (print-primitive "\n":literal)
;? ;?     (assert nil:literal)
    ; result-len = result-len + arg.length - 1 (for the 'underscore' being replaced)
    (a-len:integer <- length a:string-address/deref)
    (result-len:integer <- add result-len:integer a-len:integer)
    (result-len:integer <- subtract result-len:integer 1:literal)
;?     (print-primitive ("result-len now: " literal))
;?     (print-primitive result-len:integer)
;?     (print-primitive "\n":literal)
    (loop)
  }
  ; rewind to start of non-template args
  (_ <- input 0:literal)
  ; result = new string[result-len]
  (result:string-address <- new string:literal result-len:integer)
  ; repeatedly copy sections of template and 'holes' into result
  (result-idx:integer <- copy 0:literal)
  (i:integer <- copy 0:literal)
  { begin
    ; while arg received
    (a:string-address arg-received?:boolean <- next-input)
    (break-unless arg-received?:boolean)
    ; copy template into result until '_'
    { begin
      ; while (i < template.length)
      (tem-done?:boolean <- less-than i:integer tem-len:integer)
      (break-unless tem-done?:boolean 2:blocks)
      ; while template[i] != '_'
      (in:byte <- index template:string-address/deref i:integer)
      (underscore?:boolean <- equal in:byte ((#\_ literal)))
      (break-if underscore?:boolean)
      ; result[result-idx] = template[i]
      (out:byte-address <- index-address result:string-address/deref result-idx:integer)
      (out:byte-address/deref <- copy in:byte)
      ; ++i
      (i:integer <- add i:integer 1:literal)
      ; ++result-idx
      (result-idx:integer <- add result-idx:integer 1:literal)
      (loop)
    }
;?     (print-primitive ("i now: " literal))
;?     (print-primitive i:integer)
;?     (print-primitive "\n":literal)
    ; copy 'a' into result
    (j:integer <- copy 0:literal)
    { begin
      ; while (j < a.length)
      (arg-done?:boolean <- less-than j:integer a-len:integer)
      (break-unless arg-done?:boolean)
      ; result[result-idx] = a[j]
      (in:byte <- index a:string-address/deref j:integer)
;?       (print-primitive ("copying: " literal))
;?       (print-primitive in:byte)
;?       (print-primitive (" at: " literal))
;?       (print-primitive result-idx:integer)
;?       (print-primitive "\n":literal)
      (out:byte-address <- index-address result:string-address/deref result-idx:integer)
      (out:byte-address/deref <- copy in:byte)
      ; ++j
      (j:integer <- add j:integer 1:literal)
      ; ++result-idx
      (result-idx:integer <- add result-idx:integer 1:literal)
      (loop)
    }
    ; skip '_' in template
    (i:integer <- add i:integer 1:literal)
;?     (print-primitive ("i now: " literal))
;?     (print-primitive i:integer)
;?     (print-primitive "\n":literal)
    (loop)  ; interpolate next arg
  }
  ; done with holes; copy rest of template directly into result
  { begin
    ; while (i < template.length)
    (tem-done?:boolean <- less-than i:integer tem-len:integer)
    (break-unless tem-done?:boolean)
    ; result[result-idx] = template[i]
    (in:byte <- index template:string-address/deref i:integer)
;?     (print-primitive ("copying: " literal))
;?     (print-primitive in:byte)
;?     (print-primitive (" at: " literal))
;?     (print-primitive result-idx:integer)
;?     (print-primitive "\n":literal)
    (out:byte-address <- index-address result:string-address/deref result-idx:integer)
    (out:byte-address/deref <- copy in:byte)
    ; ++i
    (i:integer <- add i:integer 1:literal)
    ; ++result-idx
    (result-idx:integer <- add result-idx:integer 1:literal)
    (loop)
  }
  (reply result:string-address))

(init-fn find-next  ; string, character, index -> next index
  (s:string-address <- next-input)
  (needle:character <- next-input)  ; todo: unicode chars
  (idx:integer <- next-input)
  (len:integer <- length s:string-address/deref)
  { begin
    (eof?:boolean <- greater-or-equal idx:integer len:integer)
    (break-if eof?:boolean)
    (curr:byte <- index s:string-address/deref idx:integer)
    (found?:boolean <- equal curr:byte needle:character)
    (break-if found?:boolean)
    (idx:integer <- add idx:integer 1:literal)
    (loop)
  }
  (reply idx:integer))

(init-fn split  ; string, character -> string-address-array-address
  (default-scope:scope-address <- new scope:literal 30:literal)
  (s:string-address <- next-input)
  (delim:character <- next-input)  ; todo: unicode chars
  ; empty string? return empty array
  (len:integer <- length s:string-address/deref)
  { begin
    (empty?:boolean <- equal len:integer 0:literal)
    (break-unless empty?:boolean)
    (result:string-address-array-address <- new string-address-array:literal 0:literal)
    (reply result:string-address-array-address)
  }
  ; count #pieces we need room for
  (count:integer <- copy 1:literal)  ; n delimiters = n+1 pieces
  (idx:integer <- copy 0:literal)
  { begin
    (idx:integer <- find-next s:string-address delim:character idx:integer)
    (done?:boolean <- greater-or-equal idx:integer len:integer)
    (break-if done?:boolean)
    (idx:integer <- add idx:integer 1:literal)
    (count:integer <- add count:integer 1:literal)
    (loop)
  }
  ; allocate space
;?   (print-primitive (("alloc: " literal)))
;?   (print-primitive count:integer)
;?   (print-primitive (("\n" literal)))
  (result:string-address-array-address <- new string-address-array:literal count:integer)
  ; repeatedly copy slices (start..end) until delimiter into result[curr-result]
  (curr-result:integer <- copy 0:literal)
  (start:integer <- copy 0:literal)
  { begin
    ; while next delim exists
    (done?:boolean <- greater-or-equal start:integer len:integer)
    (break-if done?:boolean)
    (end:integer <- find-next s:string-address delim:character start:integer)
;?     (print-primitive (("i: " literal)))
;?     (print-primitive start:integer)
;?     (print-primitive (("-" literal)))
;?     (print-primitive end:integer)
;?     (print-primitive ((" => " literal)))
;?     (print-primitive curr-result:integer)
;?     (print-primitive (("\n" literal)))
    ; compute length of slice
    (slice-len:integer <- subtract end:integer start:integer)
    ; allocate result[curr-result]
    (dest:string-address-address <- index-address result:string-address-array-address/deref curr-result:integer)
    (dest:string-address-address/deref <- new string:literal slice-len:integer)
    ; copy start..end into result[curr-result]
    (src-idx:integer <- copy start:integer)
    (dest-idx:integer <- copy 0:literal)
    { begin
      (end-copy?:boolean <- greater-or-equal src-idx:integer end:integer)
      (break-if end-copy?:boolean)
      (src:character <- index s:string-address/deref src-idx:integer)
      (tmp:character-address <- index-address dest:string-address-address/deref/deref dest-idx:integer)
      (tmp:character-address/deref <- copy src:character)
      (src-idx:integer <- add src-idx:integer 1:literal)
      (dest-idx:integer <- add dest-idx:integer 1:literal)
      (loop)
    }
    ; slide over to next slice
    (start:integer <- add end:integer 1:literal)
    (curr-result:integer <- add curr-result:integer 1:literal)
    (loop)
  }
  (reply result:string-address-array-address)
)

)  ; section 100 for system software

;; load all provided files and start at 'main'
(reset)
(awhen (pos "--" argv)
  (map add-code:readfile (cut argv (+ it 1)))
;?   (= dump-trace* (obj whitelist '("run" "schedule" "add")))
;?   (freeze-functions)
;?   (prn function*!factorial)
  (run 'main)
  (if ($.current-charterm) ($.close-charterm))
  (prn "\nmemory: " memory*)
;?   (prn completed-routines*)
)