Implement '!' and '@' commands and add 'STATE' variable

diff --git a/main.asm b/main.asm
index 8d9c51b77573f2da465b50914b6574acb1f29679..edcba0ae9421c712218041e64d4fc0872370f8d9 100644 (file)
--- a/main.asm
+++ b/main.asm
@@ -312,6 +312,26 @@ forth_asm DOTU, '.U'
   pop rsi
   next
 
+;; Takes a value and an address, and stores the value at the given address.
+forth_asm PUT, '!'
+  pop rbx                       ; Address
+  pop rax                       ; Value
+  mov [rbx], rax
+  next
+
+;; Takes an address and returns the value at the given address.
+forth_asm GET, '@'
+  pop rax
+  mov rax, [rax]
+  push rax
+  next
+
+;; Get the location of the STATE variable. It can be set with '!' and read with
+;; '@'.
+forth STATE, 'STATE'
+  dq LIT, var_STATE
+  dq EXIT
+
 forth MAIN, 'MAIN'
   dq HELLO
   dq INTERPRET
@@ -322,6 +342,10 @@ segment readable writable
 
 latest_entry dq initial_latest_entry
 
+;; The STATE variable is 0 when the interpreter is executing, and non-zero when
+;; it is compiling.
+var_STATE dq 0
+
 FIND.rsi dq ?
 
 READ_WORD.rsi dq ?