throw error with non-register operands

.gitignore

@@ -1 +1,2 @@
 result*
+.bootle*

twasm/asm/main.asm

@@ -635,6 +635,10 @@ tokenise:
     test byte [.expecting], E_OPERAND ; make sure an operand was expected
     jz .unexpected_operand            ; if not, error
 
+    push rax
+    push rdi
+    xor eax, eax ; rax = length of operand
+
   .operand_loop:
     mov dl, [rdi]
 
@@ -645,10 +649,39 @@ tokenise:
     cmp dl, 0x00
     je .operand_break
 
-    inc rdi
+    inc rax ; inc length counter
+    inc rdi ; inc byte pointer
     jmp .operand_loop
 
   .operand_break:
+    pop rdi  ; rdi = first byte of operand
+    push rdi
+    push rsi
+    mov rsi, rax ; rsi = length of operand in bytes
+
+    mov cx, ax ; cx = length counter for safe keeping
+    call evaluate_operand
+    ; dl = return code
+    ; ax = register's token ID
+    pop rsi
+    pop rdi      ; rdi = first byte of operand
+    add di, cx   ; rdi = last byte of operand
+    mov rcx, rax ; rcx = evaluate_operand's return value
+    pop rax      ; rax = number of tokens processed
+
+    ; operand is a register
+    ; cx = token ID
+    cmp dl, 0x00
+    je .operand_register
+
+    jmp .unexpected_operand
+
+  .operand_register:
+    mov [TOKEN_TABLE_ADDR + rax * TOKEN_TABLE_ENTRY_SIZE], cx
+    inc rax ; another token processed
+    jmp .operand_break_continue
+
+  .operand_break_continue:
     mov byte [.expecting], E_COMMENT | E_NEWLINE | E_WHITESPACE | E_COMMA
     jmp .loop