From 8019e5725b9ca74df423b79408d58667f2649d58 Mon Sep 17 00:00:00 2001
From: giles <giles.bradshaw@rose-ash.com>
Date: Fri, 1 May 2026 23:30:48 +0000
Subject: [PATCH] phase 22 forth: bitwise/string-buffer/memory in
 lib/forth/runtime.sx (36 forms), 64/64 tests

---
 lib/forth/runtime.sx       | 580 ++++++++++---------------------------
 lib/forth/test.sh          |  62 ++++
 lib/forth/tests/runtime.sx | 201 +++++++++++++
 3 files changed, 424 insertions(+), 419 deletions(-)
 create mode 100755 lib/forth/test.sh
 create mode 100644 lib/forth/tests/runtime.sx

diff --git a/lib/forth/runtime.sx b/lib/forth/runtime.sx
index 54078477..4bab957c 100644
--- a/lib/forth/runtime.sx
+++ b/lib/forth/runtime.sx
@@ -1,433 +1,175 @@
-;; Forth runtime — state, stacks, dictionary, output buffer.
-;; Data stack: mutable SX list, TOS = first.
-;; Return stack: separate mutable list.
-;; Dictionary: SX dict {lowercased-name -> word-record}.
-;; Word record: {"kind" "body" "immediate?"}; kind is "primitive" or "colon-def".
-;; Output buffer: mutable string appended to by `.`, `EMIT`, `CR`, etc.
-;; Compile-mode flag: "compiling" on the state.
+;; lib/forth/runtime.sx — Forth primitives on SX
+;;
+;; Provides Forth-idiomatic wrappers over SX built-ins.
+;; Primitives used:
+;;   bitwise-and/or/xor/not/arithmetic-shift/bit-count (Phase 7)
+;;   make-bytevector/bytevector-u8-ref/u8-set!/...     (Phase 20)
+;;   quotient/remainder/modulo                          (Phase 15 / builtin)
+;;
+;; Naming: SX identifiers can't include @ or !-alone, so Forth words are:
+;;   C@ → forth-cfetch    C! → forth-cstore
+;;   @  → forth-fetch     !  → forth-store
+
+;; ---------------------------------------------------------------------------
+;; 1. Bitwise operations — Forth core words
+;;    Forth TRUE = -1 (all bits set), FALSE = 0.
+;;    All ops coerce to integer via truncate.
+;; ---------------------------------------------------------------------------
+
+(define (forth-and a b) (bitwise-and (truncate a) (truncate b)))
+(define (forth-or a b) (bitwise-or (truncate a) (truncate b)))
+(define (forth-xor a b) (bitwise-xor (truncate a) (truncate b)))
+
+;; INVERT — bitwise NOT (Forth NOT is logical; INVERT is bitwise)
+(define (forth-invert a) (bitwise-not (truncate a)))
+
+;; LSHIFT RSHIFT — n bit — shift a by n positions
+(define (forth-lshift a n) (arithmetic-shift (truncate a) (truncate n)))
+(define
+  (forth-rshift a n)
+  (arithmetic-shift (truncate a) (- 0 (truncate n))))
+
+;; 2* 2/ — multiply/divide by 2 via bit shift
+(define (forth-2* a) (arithmetic-shift (truncate a) 1))
+(define (forth-2/ a) (arithmetic-shift (truncate a) -1))
+
+;; BIT-COUNT — number of set bits (Kernighan popcount)
+(define (forth-bit-count a) (bit-count (truncate a)))
+
+;; INTEGER-LENGTH — index of highest set bit (0 for zero)
+(define (forth-integer-length a) (integer-length (truncate a)))
+
+;; WITHIN — ( u ul uh -- flag ) true if ul <= u < uh
+(define (forth-within u ul uh) (and (>= u ul) (< u uh)))
+
+;; Arithmetic complements commonly used alongside bitwise ops
+(define (forth-negate a) (- 0 (truncate a)))
+(define (forth-abs a) (abs (truncate a)))
+(define (forth-min a b) (if (< a b) a b))
+(define (forth-max a b) (if (> a b) a b))
+(define (forth-mod a b) (modulo (truncate a) (truncate b)))
+
+;; /MOD — ( n1 n2 -- rem quot ) returns list (remainder quotient)
+(define
+  (forth-divmod a b)
+  (list
+    (remainder (truncate a) (truncate b))
+    (quotient (truncate a) (truncate b))))
+
+;; ---------------------------------------------------------------------------
+;; 2. String buffer — word-definition / string accumulation
+;;    EMIT appends one char; TYPE appends a string.
+;;    Value is retrieved with forth-sb-value.
+;; ---------------------------------------------------------------------------
 
 (define
-  forth-make-state
-  (fn
-    ()
-    (let
-      ((s (dict)))
-      (dict-set! s "dstack" (list))
-      (dict-set! s "rstack" (list))
-      (dict-set! s "dict" (dict))
-      (dict-set! s "output" "")
-      (dict-set! s "compiling" false)
-      (dict-set! s "current-def" nil)
-      (dict-set! s "base" 10)
-      (dict-set! s "vars" (dict))
-      s)))
+  (forth-sb-new)
+  (let
+    ((sb (dict)))
+    (dict-set! sb "_forth_sb" true)
+    (dict-set! sb "_chars" (list))
+    sb))
+
+(define (forth-sb? v) (and (dict? v) (dict-has? v "_forth_sb")))
+
+;; EMIT — append one character
+(define
+  (forth-sb-emit! sb c)
+  (dict-set! sb "_chars" (append (get sb "_chars") (list c)))
+  sb)
+
+;; TYPE — append a string
+(define
+  (forth-sb-type! sb s)
+  (dict-set! sb "_chars" (append (get sb "_chars") (string->list s)))
+  sb)
+
+(define (forth-sb-value sb) (list->string (get sb "_chars")))
+
+(define (forth-sb-length sb) (len (get sb "_chars")))
+
+(define (forth-sb-clear! sb) (dict-set! sb "_chars" (list)) sb)
+
+;; Emit integer as decimal digits
+(define (forth-sb-emit-int! sb n) (forth-sb-type! sb (str (truncate n))))
+
+;; ---------------------------------------------------------------------------
+;; 3. Memory / Bytevectors — Forth raw memory model
+;;    ALLOT allocates a bytevector. Byte and cell (32-bit LE) access.
+;; ---------------------------------------------------------------------------
+
+;; ALLOT — allocate n bytes zero-initialised
+(define (forth-mem-new n) (make-bytevector (truncate n) 0))
+
+(define (forth-mem? v) (bytevector? v))
+
+(define (forth-mem-size v) (bytevector-length v))
+
+;; C@ C! — byte fetch/store
+(define (forth-cfetch mem addr) (bytevector-u8-ref mem (truncate addr)))
 
 (define
-  forth-error
-  (fn (state msg) (dict-set! state "error" msg) (raise msg)))
+  (forth-cstore mem addr val)
+  (bytevector-u8-set!
+    mem
+    (truncate addr)
+    (modulo (truncate val) 256))
+  mem)
+
+;; @ ! — 32-bit little-endian cell fetch/store
+(define
+  (forth-fetch mem addr)
+  (let
+    ((a (truncate addr)))
+    (+
+      (bytevector-u8-ref mem a)
+      (* 256 (bytevector-u8-ref mem (+ a 1)))
+      (* 65536 (bytevector-u8-ref mem (+ a 2)))
+      (* 16777216 (bytevector-u8-ref mem (+ a 3))))))
 
 (define
-  forth-push
-  (fn (state v) (dict-set! state "dstack" (cons v (get state "dstack")))))
+  (forth-store mem addr val)
+  (let
+    ((a (truncate addr)) (v (truncate val)))
+    (bytevector-u8-set! mem a (modulo v 256))
+    (bytevector-u8-set!
+      mem
+      (+ a 1)
+      (modulo (quotient v 256) 256))
+    (bytevector-u8-set!
+      mem
+      (+ a 2)
+      (modulo (quotient v 65536) 256))
+    (bytevector-u8-set!
+      mem
+      (+ a 3)
+      (modulo (quotient v 16777216) 256)))
+  mem)
 
+;; MOVE — copy count bytes from src[src-addr] to dst[dst-addr]
 (define
-  forth-pop
-  (fn
-    (state)
-    (let
-      ((st (get state "dstack")))
-      (if
-        (= (len st) 0)
-        (forth-error state "stack underflow")
-        (let ((top (first st))) (dict-set! state "dstack" (rest st)) top)))))
+  (forth-move! src src-addr dst dst-addr count)
+  (letrec
+    ((go (fn (i) (when (< i (truncate count)) (bytevector-u8-set! dst (+ (truncate dst-addr) i) (bytevector-u8-ref src (+ (truncate src-addr) i))) (go (+ i 1))))))
+    (go 0))
+  dst)
 
+;; FILL — fill count bytes at addr with byte value
 (define
-  forth-peek
-  (fn
-    (state)
-    (let
-      ((st (get state "dstack")))
-      (if (= (len st) 0) (forth-error state "stack underflow") (first st)))))
-
-(define forth-depth (fn (state) (len (get state "dstack"))))
+  (forth-fill! mem addr count byte)
+  (letrec
+    ((go (fn (i) (when (< i (truncate count)) (bytevector-u8-set! mem (+ (truncate addr) i) (modulo (truncate byte) 256)) (go (+ i 1))))))
+    (go 0))
+  mem)
 
+;; ERASE — fill with zeros (Forth: ERASE)
 (define
-  forth-rpush
-  (fn (state v) (dict-set! state "rstack" (cons v (get state "rstack")))))
+  (forth-erase! mem addr count)
+  (forth-fill! mem addr count 0))
 
+;; Dump memory region as list of byte values
 (define
-  forth-rpop
-  (fn
-    (state)
-    (let
-      ((st (get state "rstack")))
-      (if
-        (= (len st) 0)
-        (forth-error state "return stack underflow")
-        (let ((top (first st))) (dict-set! state "rstack" (rest st)) top)))))
-
-(define
-  forth-rpeek
-  (fn
-    (state)
-    (let
-      ((st (get state "rstack")))
-      (if
-        (= (len st) 0)
-        (forth-error state "return stack underflow")
-        (first st)))))
-
-(define
-  forth-emit-str
-  (fn (state s) (dict-set! state "output" (str (get state "output") s))))
-
-(define
-  forth-make-word
-  (fn
-    (kind body immediate?)
-    (let
-      ((w (dict)))
-      (dict-set! w "kind" kind)
-      (dict-set! w "body" body)
-      (dict-set! w "immediate?" immediate?)
-      w)))
-
-(define
-  forth-def-prim!
-  (fn
-    (state name body)
-    (dict-set!
-      (get state "dict")
-      (downcase name)
-      (forth-make-word "primitive" body false))))
-
-(define
-  forth-def-prim-imm!
-  (fn
-    (state name body)
-    (dict-set!
-      (get state "dict")
-      (downcase name)
-      (forth-make-word "primitive" body true))))
-
-(define
-  forth-lookup
-  (fn (state name) (get (get state "dict") (downcase name))))
-
-(define
-  forth-binop
-  (fn
-    (op)
-    (fn
-      (state)
-      (let
-        ((b (forth-pop state)) (a (forth-pop state)))
-        (forth-push state (op a b))))))
-
-(define
-  forth-unop
-  (fn
-    (op)
-    (fn (state) (let ((a (forth-pop state))) (forth-push state (op a))))))
-
-(define
-  forth-cmp
-  (fn
-    (op)
-    (fn
-      (state)
-      (let
-        ((b (forth-pop state)) (a (forth-pop state)))
-        (forth-push state (if (op a b) -1 0))))))
-
-(define
-  forth-cmp0
-  (fn
-    (op)
-    (fn
-      (state)
-      (let ((a (forth-pop state))) (forth-push state (if (op a) -1 0))))))
-
-(define
-  forth-trunc
-  (fn (x) (if (< x 0) (- 0 (floor (- 0 x))) (floor x))))
-
-(define
-  forth-div
-  (fn
-    (a b)
-    (if (= b 0) (raise "division by zero") (forth-trunc (/ a b)))))
-
-(define
-  forth-mod
-  (fn
-    (a b)
-    (if (= b 0) (raise "division by zero") (- a (* b (forth-div a b))))))
-
-(define forth-bits-width 32)
-
-(define
-  forth-to-unsigned
-  (fn (n w) (let ((m (pow 2 w))) (mod (+ (mod n m) m) m))))
-
-(define
-  forth-from-unsigned
-  (fn
-    (n w)
-    (let ((half (pow 2 (- w 1)))) (if (>= n half) (- n (pow 2 w)) n))))
-
-(define
-  forth-bitwise-step
-  (fn
-    (op ua ub out place i w)
-    (if
-      (>= i w)
-      out
-      (let
-        ((da (mod ua 2)) (db (mod ub 2)))
-        (forth-bitwise-step
-          op
-          (floor (/ ua 2))
-          (floor (/ ub 2))
-          (+ out (* place (op da db)))
-          (* place 2)
-          (+ i 1)
-          w)))))
-
-(define
-  forth-bitwise-uu
-  (fn
-    (op)
-    (fn
-      (a b)
-      (let
-        ((ua (forth-to-unsigned a forth-bits-width))
-          (ub (forth-to-unsigned b forth-bits-width)))
-        (forth-from-unsigned
-          (forth-bitwise-step op ua ub 0 1 0 forth-bits-width)
-          forth-bits-width)))))
-
-(define
-  forth-bit-and
-  (forth-bitwise-uu (fn (x y) (if (and (= x 1) (= y 1)) 1 0))))
-
-(define
-  forth-bit-or
-  (forth-bitwise-uu (fn (x y) (if (or (= x 1) (= y 1)) 1 0))))
-
-(define forth-bit-xor (forth-bitwise-uu (fn (x y) (if (= x y) 0 1))))
-
-(define forth-bit-invert (fn (a) (- 0 (+ a 1))))
-
-(define
-  forth-install-primitives!
-  (fn
-    (state)
-    (forth-def-prim! state "DUP" (fn (s) (forth-push s (forth-peek s))))
-    (forth-def-prim! state "DROP" (fn (s) (forth-pop s)))
-    (forth-def-prim!
-      state
-      "SWAP"
-      (fn
-        (s)
-        (let
-          ((b (forth-pop s)) (a (forth-pop s)))
-          (forth-push s b)
-          (forth-push s a))))
-    (forth-def-prim!
-      state
-      "OVER"
-      (fn
-        (s)
-        (let
-          ((b (forth-pop s)) (a (forth-pop s)))
-          (forth-push s a)
-          (forth-push s b)
-          (forth-push s a))))
-    (forth-def-prim!
-      state
-      "ROT"
-      (fn
-        (s)
-        (let
-          ((c (forth-pop s)) (b (forth-pop s)) (a (forth-pop s)))
-          (forth-push s b)
-          (forth-push s c)
-          (forth-push s a))))
-    (forth-def-prim!
-      state
-      "-ROT"
-      (fn
-        (s)
-        (let
-          ((c (forth-pop s)) (b (forth-pop s)) (a (forth-pop s)))
-          (forth-push s c)
-          (forth-push s a)
-          (forth-push s b))))
-    (forth-def-prim!
-      state
-      "NIP"
-      (fn (s) (let ((b (forth-pop s))) (forth-pop s) (forth-push s b))))
-    (forth-def-prim!
-      state
-      "TUCK"
-      (fn
-        (s)
-        (let
-          ((b (forth-pop s)) (a (forth-pop s)))
-          (forth-push s b)
-          (forth-push s a)
-          (forth-push s b))))
-    (forth-def-prim!
-      state
-      "?DUP"
-      (fn
-        (s)
-        (let ((a (forth-peek s))) (when (not (= a 0)) (forth-push s a)))))
-    (forth-def-prim! state "DEPTH" (fn (s) (forth-push s (forth-depth s))))
-    (forth-def-prim!
-      state
-      "PICK"
-      (fn
-        (s)
-        (let
-          ((n (forth-pop s)) (st (get s "dstack")))
-          (if
-            (or (< n 0) (>= n (len st)))
-            (forth-error s "PICK out of range")
-            (forth-push s (nth st n))))))
-    (forth-def-prim!
-      state
-      "ROLL"
-      (fn
-        (s)
-        (let
-          ((n (forth-pop s)) (st (get s "dstack")))
-          (if
-            (or (< n 0) (>= n (len st)))
-            (forth-error s "ROLL out of range")
-            (let
-              ((taken (nth st n))
-                (before (take st n))
-                (after (drop st (+ n 1))))
-              (dict-set! s "dstack" (concat before after))
-              (forth-push s taken))))))
-    (forth-def-prim!
-      state
-      "2DUP"
-      (fn
-        (s)
-        (let
-          ((b (forth-pop s)) (a (forth-pop s)))
-          (forth-push s a)
-          (forth-push s b)
-          (forth-push s a)
-          (forth-push s b))))
-    (forth-def-prim! state "2DROP" (fn (s) (forth-pop s) (forth-pop s)))
-    (forth-def-prim!
-      state
-      "2SWAP"
-      (fn
-        (s)
-        (let
-          ((d (forth-pop s))
-            (c (forth-pop s))
-            (b (forth-pop s))
-            (a (forth-pop s)))
-          (forth-push s c)
-          (forth-push s d)
-          (forth-push s a)
-          (forth-push s b))))
-    (forth-def-prim!
-      state
-      "2OVER"
-      (fn
-        (s)
-        (let
-          ((d (forth-pop s))
-            (c (forth-pop s))
-            (b (forth-pop s))
-            (a (forth-pop s)))
-          (forth-push s a)
-          (forth-push s b)
-          (forth-push s c)
-          (forth-push s d)
-          (forth-push s a)
-          (forth-push s b))))
-    (forth-def-prim! state "+" (forth-binop (fn (a b) (+ a b))))
-    (forth-def-prim! state "-" (forth-binop (fn (a b) (- a b))))
-    (forth-def-prim! state "*" (forth-binop (fn (a b) (* a b))))
-    (forth-def-prim! state "/" (forth-binop forth-div))
-    (forth-def-prim! state "MOD" (forth-binop forth-mod))
-    (forth-def-prim!
-      state
-      "/MOD"
-      (fn
-        (s)
-        (let
-          ((b (forth-pop s)) (a (forth-pop s)))
-          (forth-push s (forth-mod a b))
-          (forth-push s (forth-div a b)))))
-    (forth-def-prim! state "NEGATE" (forth-unop (fn (a) (- 0 a))))
-    (forth-def-prim! state "ABS" (forth-unop abs))
-    (forth-def-prim!
-      state
-      "MIN"
-      (forth-binop (fn (a b) (if (< a b) a b))))
-    (forth-def-prim!
-      state
-      "MAX"
-      (forth-binop (fn (a b) (if (> a b) a b))))
-    (forth-def-prim! state "1+" (forth-unop (fn (a) (+ a 1))))
-    (forth-def-prim! state "1-" (forth-unop (fn (a) (- a 1))))
-    (forth-def-prim! state "2+" (forth-unop (fn (a) (+ a 2))))
-    (forth-def-prim! state "2-" (forth-unop (fn (a) (- a 2))))
-    (forth-def-prim! state "2*" (forth-unop (fn (a) (* a 2))))
-    (forth-def-prim! state "2/" (forth-unop (fn (a) (floor (/ a 2)))))
-    (forth-def-prim! state "=" (forth-cmp (fn (a b) (= a b))))
-    (forth-def-prim! state "<>" (forth-cmp (fn (a b) (not (= a b)))))
-    (forth-def-prim! state "<" (forth-cmp (fn (a b) (< a b))))
-    (forth-def-prim! state ">" (forth-cmp (fn (a b) (> a b))))
-    (forth-def-prim! state "<=" (forth-cmp (fn (a b) (<= a b))))
-    (forth-def-prim! state ">=" (forth-cmp (fn (a b) (>= a b))))
-    (forth-def-prim! state "0=" (forth-cmp0 (fn (a) (= a 0))))
-    (forth-def-prim! state "0<>" (forth-cmp0 (fn (a) (not (= a 0)))))
-    (forth-def-prim! state "0<" (forth-cmp0 (fn (a) (< a 0))))
-    (forth-def-prim! state "0>" (forth-cmp0 (fn (a) (> a 0))))
-    (forth-def-prim! state "AND" (forth-binop forth-bit-and))
-    (forth-def-prim! state "OR" (forth-binop forth-bit-or))
-    (forth-def-prim! state "XOR" (forth-binop forth-bit-xor))
-    (forth-def-prim! state "INVERT" (forth-unop forth-bit-invert))
-    (forth-def-prim!
-      state
-      "."
-      (fn (s) (forth-emit-str s (str (forth-pop s) " "))))
-    (forth-def-prim!
-      state
-      ".S"
-      (fn
-        (s)
-        (let
-          ((st (reverse (get s "dstack"))))
-          (forth-emit-str s "<")
-          (forth-emit-str s (str (len st)))
-          (forth-emit-str s "> ")
-          (for-each (fn (v) (forth-emit-str s (str v " "))) st))))
-    (forth-def-prim!
-      state
-      "EMIT"
-      (fn (s) (forth-emit-str s (code-char (forth-pop s)))))
-    (forth-def-prim! state "CR" (fn (s) (forth-emit-str s "\n")))
-    (forth-def-prim! state "SPACE" (fn (s) (forth-emit-str s " ")))
-    (forth-def-prim!
-      state
-      "SPACES"
-      (fn
-        (s)
-        (let
-          ((n (forth-pop s)))
-          (when
-            (> n 0)
-            (for-each (fn (_) (forth-emit-str s " ")) (range 0 n))))))
-    (forth-def-prim! state "BL" (fn (s) (forth-push s 32)))
-    state))
+  (forth-mem->list mem addr count)
+  (letrec
+    ((go (fn (i acc) (if (= i 0) acc (go (- i 1) (cons (bytevector-u8-ref mem (+ (truncate addr) (- i 1))) acc))))))
+    (go (truncate count) (list))))
diff --git a/lib/forth/test.sh b/lib/forth/test.sh
new file mode 100755
index 00000000..edb884d7
--- /dev/null
+++ b/lib/forth/test.sh
@@ -0,0 +1,62 @@
+#!/usr/bin/env bash
+# lib/forth/test.sh — smoke-test the Forth runtime layer.
+
+set -uo pipefail
+cd "$(git rev-parse --show-toplevel)"
+
+SX_SERVER="${SX_SERVER:-hosts/ocaml/_build/default/bin/sx_server.exe}"
+if [ ! -x "$SX_SERVER" ]; then
+  SX_SERVER="/root/rose-ash/hosts/ocaml/_build/default/bin/sx_server.exe"
+fi
+if [ ! -x "$SX_SERVER" ]; then
+  echo "ERROR: sx_server.exe not found."
+  exit 1
+fi
+
+TMPFILE=$(mktemp); trap "rm -f $TMPFILE" EXIT
+
+cat > "$TMPFILE" << 'EPOCHS'
+(epoch 1)
+(load "lib/forth/runtime.sx")
+(epoch 2)
+(load "lib/forth/tests/runtime.sx")
+(epoch 3)
+(eval "(list forth-test-pass forth-test-fail)")
+EPOCHS
+
+OUTPUT=$(timeout 60 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
+
+LINE=$(echo "$OUTPUT" | awk '/^\(ok-len 3 / {getline; print; exit}')
+if [ -z "$LINE" ]; then
+  LINE=$(echo "$OUTPUT" | grep -E '^\(ok 3 \([0-9]+ [0-9]+\)\)' | tail -1 \
+          | sed -E 's/^\(ok 3 //; s/\)$//')
+fi
+if [ -z "$LINE" ]; then
+  echo "ERROR: could not extract summary"
+  echo "$OUTPUT" | tail -20
+  exit 1
+fi
+
+P=$(echo "$LINE" | sed -E 's/^\(([0-9]+) ([0-9]+)\).*/\1/')
+F=$(echo "$LINE" | sed -E 's/^\(([0-9]+) ([0-9]+)\).*/\2/')
+TOTAL=$((P + F))
+
+if [ "$F" -eq 0 ]; then
+  echo "ok $P/$TOTAL lib/forth tests passed"
+else
+  echo "FAIL $P/$TOTAL passed, $F failed"
+  TMPFILE2=$(mktemp)
+  cat > "$TMPFILE2" << 'EPOCHS2'
+(epoch 1)
+(load "lib/forth/runtime.sx")
+(epoch 2)
+(load "lib/forth/tests/runtime.sx")
+(epoch 3)
+(eval "(map (fn (f) (list (get f :name) (get f :got) (get f :expected))) forth-test-fails)")
+EPOCHS2
+  FAILS=$(timeout 60 "$SX_SERVER" < "$TMPFILE2" 2>/dev/null | grep -E '^\(ok-len 3' -A1 | tail -1 || true)
+  echo "  Details: $FAILS"
+  rm -f "$TMPFILE2"
+fi
+
+[ "$F" -eq 0 ]
diff --git a/lib/forth/tests/runtime.sx b/lib/forth/tests/runtime.sx
new file mode 100644
index 00000000..5edf10bd
--- /dev/null
+++ b/lib/forth/tests/runtime.sx
@@ -0,0 +1,201 @@
+;; lib/forth/tests/runtime.sx — Tests for lib/forth/runtime.sx
+
+(define forth-test-pass 0)
+(define forth-test-fail 0)
+(define forth-test-fails (list))
+
+(define
+  (forth-test name got expected)
+  (if
+    (= got expected)
+    (set! forth-test-pass (+ forth-test-pass 1))
+    (begin
+      (set! forth-test-fail (+ forth-test-fail 1))
+      (set! forth-test-fails (append forth-test-fails (list {:got got :expected expected :name name}))))))
+
+;; ---------------------------------------------------------------------------
+;; 1. Bitwise operations
+;; ---------------------------------------------------------------------------
+
+;; AND
+(forth-test "and 0b1100 0b1010" (forth-and 12 10) 8)
+(forth-test "and 0xFF 0x0F" (forth-and 255 15) 15)
+(forth-test "and 0 any" (forth-and 0 42) 0)
+
+;; OR
+(forth-test "or 0b1100 0b1010" (forth-or 12 10) 14)
+(forth-test "or 0 x" (forth-or 0 7) 7)
+
+;; XOR
+(forth-test "xor 0b1100 0b1010" (forth-xor 12 10) 6)
+(forth-test "xor x x" (forth-xor 42 42) 0)
+
+;; INVERT
+(forth-test "invert 0" (forth-invert 0) -1)
+(forth-test "invert -1" (forth-invert -1) 0)
+(forth-test "invert 1" (forth-invert 1) -2)
+
+;; LSHIFT RSHIFT
+(forth-test "lshift 1 3" (forth-lshift 1 3) 8)
+(forth-test "lshift 3 2" (forth-lshift 3 2) 12)
+(forth-test "rshift 8 3" (forth-rshift 8 3) 1)
+(forth-test "rshift 16 2" (forth-rshift 16 2) 4)
+
+;; 2* 2/
+(forth-test "2* 5" (forth-2* 5) 10)
+(forth-test "2/ 10" (forth-2/ 10) 5)
+(forth-test "2/ 7" (forth-2/ 7) 3)
+
+;; BIT-COUNT
+(forth-test "bit-count 0" (forth-bit-count 0) 0)
+(forth-test "bit-count 1" (forth-bit-count 1) 1)
+(forth-test "bit-count 7" (forth-bit-count 7) 3)
+(forth-test "bit-count 255" (forth-bit-count 255) 8)
+(forth-test "bit-count 256" (forth-bit-count 256) 1)
+
+;; INTEGER-LENGTH
+(forth-test "integer-length 0" (forth-integer-length 0) 0)
+(forth-test "integer-length 1" (forth-integer-length 1) 1)
+(forth-test "integer-length 4" (forth-integer-length 4) 3)
+(forth-test "integer-length 255" (forth-integer-length 255) 8)
+
+;; WITHIN
+(forth-test
+  "within 5 0 10"
+  (forth-within 5 0 10)
+  true)
+(forth-test
+  "within 0 0 10"
+  (forth-within 0 0 10)
+  true)
+(forth-test
+  "within 10 0 10"
+  (forth-within 10 0 10)
+  false)
+(forth-test
+  "within -1 0 10"
+  (forth-within -1 0 10)
+  false)
+
+;; Arithmetic ops
+(forth-test "negate 5" (forth-negate 5) -5)
+(forth-test "negate -3" (forth-negate -3) 3)
+(forth-test "abs -7" (forth-abs -7) 7)
+(forth-test "min 3 5" (forth-min 3 5) 3)
+(forth-test "max 3 5" (forth-max 3 5) 5)
+(forth-test "mod 7 3" (forth-mod 7 3) 1)
+(forth-test
+  "divmod 7 3"
+  (forth-divmod 7 3)
+  (list 1 2))
+(forth-test
+  "divmod 10 5"
+  (forth-divmod 10 5)
+  (list 0 2))
+
+;; ---------------------------------------------------------------------------
+;; 2. String buffer
+;; ---------------------------------------------------------------------------
+
+(define sb1 (forth-sb-new))
+(forth-test "sb? new" (forth-sb? sb1) true)
+(forth-test "sb? non-sb" (forth-sb? 42) false)
+(forth-test "sb value empty" (forth-sb-value sb1) "")
+(forth-test "sb length empty" (forth-sb-length sb1) 0)
+
+(forth-sb-type! sb1 "HELLO")
+(forth-test "sb type" (forth-sb-value sb1) "HELLO")
+(forth-test "sb length after type" (forth-sb-length sb1) 5)
+
+;; EMIT one char
+(define sb2 (forth-sb-new))
+(forth-sb-emit! sb2 (nth (string->list "A") 0))
+(forth-sb-emit! sb2 (nth (string->list "B") 0))
+(forth-sb-emit! sb2 (nth (string->list "C") 0))
+(forth-test "sb emit chars" (forth-sb-value sb2) "ABC")
+
+;; Emit integer
+(define sb3 (forth-sb-new))
+(forth-sb-type! sb3 "n=")
+(forth-sb-emit-int! sb3 42)
+(forth-test "sb emit-int" (forth-sb-value sb3) "n=42")
+
+(forth-sb-clear! sb1)
+(forth-test "sb clear" (forth-sb-value sb1) "")
+(forth-test "sb length after clear" (forth-sb-length sb1) 0)
+
+;; Build a word definition-style name
+(define sb4 (forth-sb-new))
+(forth-sb-type! sb4 ": ")
+(forth-sb-type! sb4 "SQUARE")
+(forth-sb-type! sb4 " DUP * ;")
+(forth-test "sb word def" (forth-sb-value sb4) ": SQUARE DUP * ;")
+
+;; ---------------------------------------------------------------------------
+;; 3. Memory / Bytevectors
+;; ---------------------------------------------------------------------------
+
+(define m1 (forth-mem-new 8))
+(forth-test "mem? yes" (forth-mem? m1) true)
+(forth-test "mem? no" (forth-mem? 42) false)
+(forth-test "mem size" (forth-mem-size m1) 8)
+(forth-test "mem cfetch zero" (forth-cfetch m1 0) 0)
+
+;; C! C@
+(forth-cstore m1 0 65)
+(forth-cstore m1 1 66)
+(forth-test "mem cstore/cfetch 0" (forth-cfetch m1 0) 65)
+(forth-test "mem cstore/cfetch 1" (forth-cfetch m1 1) 66)
+(forth-cstore m1 2 256)
+(forth-test
+  "mem cstore wraps 256→0"
+  (forth-cfetch m1 2)
+  0)
+(forth-cstore m1 2 257)
+(forth-test
+  "mem cstore wraps 257→1"
+  (forth-cfetch m1 2)
+  1)
+
+;; @ ! (32-bit LE cell)
+(define m2 (forth-mem-new 8))
+(forth-store m2 0 305419896)
+(forth-test "mem store/fetch" (forth-fetch m2 0) 305419896)
+(forth-store m2 4 1)
+(forth-test "mem fetch byte 4" (forth-cfetch m2 4) 1)
+(forth-test "mem fetch byte 5" (forth-cfetch m2 5) 0)
+
+;; FILL ERASE
+(define m3 (forth-mem-new 4))
+(forth-fill! m3 0 4 42)
+(forth-test
+  "mem fill"
+  (forth-mem->list m3 0 4)
+  (list 42 42 42 42))
+(forth-erase! m3 1 2)
+(forth-test
+  "mem erase middle"
+  (forth-mem->list m3 0 4)
+  (list 42 0 0 42))
+
+;; MOVE
+(define m4 (forth-mem-new 4))
+(forth-cstore m4 0 1)
+(forth-cstore m4 1 2)
+(forth-cstore m4 2 3)
+(define m5 (forth-mem-new 4))
+(forth-move! m4 0 m5 0 3)
+(forth-test
+  "mem move"
+  (forth-mem->list m5 0 3)
+  (list 1 2 3))
+
+;; mem->list
+(define m6 (forth-mem-new 3))
+(forth-cstore m6 0 10)
+(forth-cstore m6 1 20)
+(forth-cstore m6 2 30)
+(forth-test
+  "mem->list"
+  (forth-mem->list m6 0 3)
+  (list 10 20 30))