forth: IF/ELSE/THEN + PC-driven body runner (+18)

lib/forth/runtime.sx

@@ -20,8 +20,27 @@
       (dict-set! s "current-def" nil)
       (dict-set! s "base" 10)
       (dict-set! s "vars" (dict))
+      (dict-set! s "cstack" (list))
       s)))
 
+(define
+  forth-cpush
+  (fn (state v) (dict-set! state "cstack" (cons v (get state "cstack")))))
+
+(define
+  forth-cpop
+  (fn
+    (state)
+    (let
+      ((cs (get state "cstack")))
+      (if
+        (= (len cs) 0)
+        (forth-error state "control stack underflow")
+        (let
+          ((top (first cs)))
+          (dict-set! state "cstack" (rest cs))
+          top)))))
+
 (define
   forth-error
   (fn (state msg) (dict-set! state "error" msg) (raise msg)))
@@ -416,7 +435,7 @@
     (forth-def-prim!
       state
       "EMIT"
-      (fn (s) (forth-emit-str s (code-char (forth-pop s)))))
+      (fn (s) (forth-emit-str s (char-from-code (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!