Add a halt mechanism

wipforth.wat

@@ -19,6 +19,9 @@
  (global $cfa (mut i32) (i32.const 0))
  (global $fn  (mut i32) (i32.const 0))
 
+ ;; Trampoline control flag
+ (global $run (mut i32) (i32.const 0))
+
  ;; Some little helper functions
 
  (func $push (param $x i32)
@@ -585,6 +588,8 @@
        i32.load
        global.set $fn)
 
+ (func $halt i32.const 0 global.set $run)
+
  ;; Return and parameter stack primitives
 
  (func $tor
@@ -1118,13 +1123,13 @@
        "\64\05\00\00"
        "\04HERE\00\00\00"
        "\02\00\00\00"
-       "\c0\0b\00\00")
+       "\10\0c\00\00")
 
  (data (i32.const 0x058c)
        "\78\05\00\00"
        "\06LATEST\00"
        "\02\00\00\00"
-       "\b0\0b\00\00")
+       "\00\0c\00\00")
 
  (data (i32.const 0x05a0)
        "\8c\05\00\00"
@@ -1749,6 +1754,12 @@
        "\04COPY\00\00\00"
        "\3d\00\00\00")
 
+ (elem (i32.const 0x3e) $halt)
+ (data (i32.const 0x0c00)
+       "\f0\0b\00\00"
+       "\04HALT\00\00\00"
+       "\3e\00\00\00")
+
  ;; The trampoline is a workaround for WebAssembly's lack of indirect
  ;; jumps and code addresses.  Instead of jumping into the next
  ;; codeword, NEXT sets the $fn global to the function index of the
@@ -1760,9 +1771,8 @@
 
  (func $trampoline
        loop $loop
-         global.get $fn
-         call_indirect (type $codeword)
-         br $loop
+         global.get $fn call_indirect (type $codeword)
+         global.get $run br_if $loop
        end)
 
  (func (export "reset")
@@ -1770,4 +1780,6 @@
        i32.const 0xf000 global.set $sp   ;; Set the stack pointer
        i32.const 0x0bac global.set $ip   ;; Set the IP to the cold start
        call $next
+
+       i32.const 1 global.set $run
        call $trampoline))