Add dup, rot, and over to Forbble example

src/examples/forbble.pbl

@@ -48,6 +48,16 @@
 (def ^ "^")
 (def $ "$")
 (def swap "swap")
+(def dup "dup")
+(def rot "rot")
+(def over "over")
+
+; Duplicate the top element of the stack
+(def _dup (fn (_) (
+  (def _top (at 0 stack))
+  (if (iserr _top) (prnl "dup: STACK EMPTY")
+    (stkadd _top))
+)))
 
 ; Swap the top two elements of the stack, if possible
 (def _swap (fn (_) (
@@ -58,6 +68,24 @@
     (prnl "swap: STACK TOO SMALL")
   ))))
 
+; Rotate the third element to be above the first and second elements
+(def _rot (fn (_) (
+  (if (> (len stack) 2) (
+    (def (_c _b _a) ((bop 0) (bop 0) (bop 0)))
+      (stkadd _b)
+      (stkadd _c)
+      (stkadd _a))
+    (prnl "rot: STACK TOO SMALL")
+  ))))
+
+; Rotate the third element to be above the first and second elements
+(def _over (fn (_) (
+  (if (> (len stack) 1) (
+    (def _a (at 1 stack))
+      (stkadd _a))
+    (prnl "over: STACK TOO SMALL")
+  ))))
+
 ; Defines a given symbol using a given list of Forth inputs
 (def compile (fn (func sym) (
   (def _x (at 0 func))
@@ -78,6 +106,9 @@
     (if (= * _x) (twop *)
     (if (= / _x) (twop /)
     (if (= "swap" _x) (_swap 0)
+    (if (= "dup" _x) (_dup 0)
+    (if (= "rot" _x) (_rot 0)
+    (if (= "over" _x) (_over 0)
     (if (= "^" _x) (pch (bop 0))
     (if (= ":" _x) ( ; Compile a phrase into the next symbol
       (def var (at 1 list))
@@ -88,7 +119,7 @@
         (def _e (eval _x))
         (if (iserr (len _e)) () (feval _e))
       )
-    )))))))))
+    ))))))))))))
     ; A switch/case operator might be good, to avoid huge closing-paren chains
 
     ; If any list is left, recurse into it
@@ -113,10 +144,16 @@
 (feval (: "in" $))
 (feval (: "i>f" 1 ft / $))
 (feval (: "i>y" 1 yd / $))
+
 ; Convert between Farenheit and Celcius
 (feval (: "f>c" 32 - 5 * 9 /$))
 (feval (: "c>f" 9 * 5 / 32 + $))
 
+; Math
+(feval (: "sq" dup * $))
+; Gets next Fibonacci number from two on stack
+(feval (: "fib" swap over + dup . $))
+
 ; A simple REPL. Exits on 'q'
 (def repl (fn (_) (
   (prn "forbble::> ")