diff --git a/lib/guest/lex.sx b/lib/guest/lex.sx
new file mode 100644
index 00000000..5894dffa
--- /dev/null
+++ b/lib/guest/lex.sx
@@ -0,0 +1,67 @@
+;; lib/guest/lex.sx — character-class predicates and token primitives shared
+;; across guest tokenisers.
+;;
+;; All predicates are nil-safe — they accept nil (end-of-input) and return
+;; false. This matches the convention used by the existing per-language
+;; tokenisers (cur returns nil at EOF).
+;;
+;; Char classes
+;; ------------
+;;   lex-digit?       — 0-9
+;;   lex-hex-digit?   — 0-9, a-f, A-F
+;;   lex-alpha?       — a-z, A-Z (alias: lex-letter?)
+;;   lex-alnum?       — alpha or digit
+;;   lex-ident-start? — alpha or underscore
+;;   lex-ident-char?  — ident-start or digit
+;;   lex-space?       — " ", "\t", "\r"           (no newline)
+;;   lex-whitespace?  — " ", "\t", "\r", "\n"     (includes newline)
+;;
+;; Token record
+;; ------------
+;;   (lex-make-token TYPE VALUE POS)        — {:type :value :pos}
+;;   (lex-make-token-spanning TYPE VALUE POS END)
+;;                                          — {:type :value :pos :end}
+;;   (lex-token-type TOK)
+;;   (lex-token-value TOK)
+;;   (lex-token-pos TOK)
+
+(define lex-digit? (fn (c) (and (not (= c nil)) (>= c "0") (<= c "9"))))
+
+(define
+  lex-hex-digit?
+  (fn
+    (c)
+    (and
+      (not (= c nil))
+      (or
+        (lex-digit? c)
+        (and (>= c "a") (<= c "f"))
+        (and (>= c "A") (<= c "F"))))))
+
+(define
+  lex-alpha?
+  (fn
+    (c)
+    (and
+      (not (= c nil))
+      (or (and (>= c "a") (<= c "z")) (and (>= c "A") (<= c "Z"))))))
+
+(define lex-letter? lex-alpha?)
+
+(define lex-alnum? (fn (c) (or (lex-alpha? c) (lex-digit? c))))
+
+(define lex-ident-start? (fn (c) (or (lex-alpha? c) (= c "_"))))
+
+(define lex-ident-char? (fn (c) (or (lex-ident-start? c) (lex-digit? c))))
+
+(define lex-space? (fn (c) (or (= c " ") (= c "\t") (= c "\r"))))
+
+(define lex-whitespace? (fn (c) (or (lex-space? c) (= c "\n"))))
+
+(define lex-make-token (fn (type value pos) {:pos pos :value value :type type}))
+
+(define lex-make-token-spanning (fn (type value pos end) {:pos pos :end end :value value :type type}))
+
+(define lex-token-type (fn (tok) (get tok :type)))
+(define lex-token-value (fn (tok) (get tok :value)))
+(define lex-token-pos (fn (tok) (get tok :pos)))
diff --git a/lib/lua/test.sh b/lib/lua/test.sh
index 719f3750..13dabffc 100755
--- a/lib/lua/test.sh
+++ b/lib/lua/test.sh
@@ -28,6 +28,8 @@ trap "rm -f $TMPFILE" EXIT
 
 cat > "$TMPFILE" << 'EPOCHS'
 (epoch 1)
+(load "lib/guest/lex.sx")
+(load "lib/guest/prefix.sx")
 (load "lib/lua/tokenizer.sx")
 (epoch 2)
 (load "lib/lua/parser.sx")
diff --git a/lib/lua/tokenizer.sx b/lib/lua/tokenizer.sx
index 6a09788d..32512705 100644
--- a/lib/lua/tokenizer.sx
+++ b/lib/lua/tokenizer.sx
@@ -1,31 +1,12 @@
-(define lua-make-token (fn (type value pos) {:pos pos :value value :type type}))
+(prefix-rename "lua-"
+  '((make-token   lex-make-token)
+    (digit?       lex-digit?)
+    (hex-digit?   lex-hex-digit?)
+    (letter?      lex-alpha?)
+    (ident-start? lex-ident-start?)
+    (ident-char?  lex-ident-char?)
+    (ws?          lex-whitespace?)))
 
-(define lua-digit? (fn (c) (and (not (= c nil)) (>= c "0") (<= c "9"))))
-
-(define
-  lua-hex-digit?
-  (fn
-    (c)
-    (and
-      (not (= c nil))
-      (or
-        (lua-digit? c)
-        (and (>= c "a") (<= c "f"))
-        (and (>= c "A") (<= c "F"))))))
-
-(define
-  lua-letter?
-  (fn
-    (c)
-    (and
-      (not (= c nil))
-      (or (and (>= c "a") (<= c "z")) (and (>= c "A") (<= c "Z"))))))
-
-(define lua-ident-start? (fn (c) (or (lua-letter? c) (= c "_"))))
-
-(define lua-ident-char? (fn (c) (or (lua-ident-start? c) (lua-digit? c))))
-
-(define lua-ws? (fn (c) (or (= c " ") (= c "\t") (= c "\n") (= c "\r"))))
 
 (define
   lua-keywords
diff --git a/lib/tcl/conformance.sh b/lib/tcl/conformance.sh
index 50d0f8d0..23ce41fb 100755
--- a/lib/tcl/conformance.sh
+++ b/lib/tcl/conformance.sh
@@ -63,6 +63,8 @@ for tcl_file in "${TCL_FILES[@]}"; do
   # Build epoch input using quoted heredoc for static parts; helper path via variable
   cat > "$tmpfile" << EPOCHS
 (epoch 1)
+(load "lib/guest/lex.sx")
+(load "lib/guest/prefix.sx")
 (load "lib/tcl/tokenizer.sx")
 (epoch 2)
 (load "lib/tcl/parser.sx")
diff --git a/lib/tcl/test.sh b/lib/tcl/test.sh
index 445db51d..8b85edde 100755
--- a/lib/tcl/test.sh
+++ b/lib/tcl/test.sh
@@ -33,6 +33,8 @@ HELPER_EOF
 
 cat > "$TMPFILE" << EPOCHS
 (epoch 1)
+(load "lib/guest/lex.sx")
+(load "lib/guest/prefix.sx")
 (load "lib/tcl/tokenizer.sx")
 (epoch 2)
 (load "lib/tcl/parser.sx")
diff --git a/lib/tcl/tokenizer.sx b/lib/tcl/tokenizer.sx
index 6ad455ac..bc094ff3 100644
--- a/lib/tcl/tokenizer.sx
+++ b/lib/tcl/tokenizer.sx
@@ -1,19 +1,10 @@
-(define tcl-ws? (fn (c) (or (= c " ") (= c "\t") (= c "\r"))))
+(prefix-rename "tcl-"
+  '((ws?          lex-space?)
+    (alpha?       lex-alpha?)
+    (digit?       lex-digit?)
+    (ident-start? lex-ident-start?)
+    (ident-char?  lex-ident-char?)))
 
-(define tcl-alpha?
-  (fn (c)
-    (and
-      (not (= c nil))
-      (or (and (>= c "a") (<= c "z")) (and (>= c "A") (<= c "Z"))))))
-
-(define tcl-digit?
-  (fn (c) (and (not (= c nil)) (>= c "0") (<= c "9"))))
-
-(define tcl-ident-start?
-  (fn (c) (or (tcl-alpha? c) (= c "_"))))
-
-(define tcl-ident-char?
-  (fn (c) (or (tcl-ident-start? c) (tcl-digit? c))))
 
 (define tcl-tokenize
   (fn (src)