ttc run: added let, Python expr to print and assert

@@ -179,37 +179,6 @@ class Runner (object) :
             args.append(f"=> {_val(ret)}")
         return (f"{F.WHITE}{event}", *args)
 
-class AssertEnv (dict) :
-    def __init__ (self, ttc, *l, **k) :
-        super().__init__(*l, **k)
-        self.ttc = ttc
-    def __getitem__ (self, key) :
-        if not isinstance(key, str) :
-            raise TypeError(f"expected 'str' key, got {type(key).__name__!r}")
-        key = key.upper()
-        if (reg := regnum.get(key, None)) is not None :
-            return self.ttc.cpu.reg[reg]
-        elif key == "INTR" :
-            return list(self.ttc.cpu.intr)
-        elif key == "MASK" :
-            MR = self.ttc.cpu.reg[regnum["MR"]]
-            return [int(m) for m in bin(MR)[2:].rjust(16, "1")]
-        elif key == "CLOCK" :
-            return self.ttc.cpu.clock
-        elif key.startswith("[") and key.endswith("]") :
-            addr = key[1:-1]
-            if ":" in addr :
-                start, stop = addr.split(":", 1)
-                start = int(start or "0", 16)
-                stop = int(stop or "FFFF", 16)
-                return list(self.ttc.ram.ram[start:stop+1])
-            else :
-                return self.ttc.ram.ram[int(addr, 16)]
-        elif key == "SCREEN" :
-            return self.ttc.screen.ascii()
-        else :
-            raise KeyError(key)
-
 class ShellRunner (Runner) :
     _prompt = "ttc >>>"
     prompt = f"{S.BRIGHT}{_prompt}{S.RESET_ALL} "
@@ -223,6 +192,7 @@ class ShellRunner (Runner) :
         readline.set_completer(self.complete)
         self.script = self.parse_script(script)
         self.interactive = interactive
+        self.eval_env = {}
     def err (self, msg) :
         if self.interactive :
             super().err(msg)
@@ -362,6 +332,36 @@ class ShellRunner (Runner) :
         else :
             await self.sim.ui_expect(*args)
             return False
+    async def cmd_let (self, name:str, expr:str=None) :
+        """saves a value as a name
+         - name: name to be assigned
+         - expr: value expression as a Python expression involving
+            - the names already assigned with let
+            - registers names
+            - the interrupt vector INTR (list of 0/1)
+            - the interrupt mask MASK (list of 0/1)
+            - the clock tick counter CLOCK
+            - the memory RAM (list of ints)
+            - the screen text SCREEN (str)
+        """
+        if expr is None :
+            self.eval_env.pop(name, None)
+        else :
+            self.eval_env[name] = self.eval(expr)
+    def eval (self, expr, loc={}) :
+        try :
+            return int(expr, 16)
+        except :
+            env = self.eval_env.copy()
+            for reg, num in regnum.items() :
+                env[reg] = self.ttc.cpu.reg[num]
+            env["INTR"] = list(self.ttc.cpu.intr)
+            MR = self.ttc.cpu.reg[regnum["MR"]]
+            env["MASK"] = [int(m) for m in bin(MR)[2:].rjust(16, "1")]
+            env["CLOCK"] = self.ttc.cpu.clock
+            env["RAM"] = list(self.ttc.ram.ram)
+            env["SCREEN"] = self.ttc.screen.ascii()
+            return eval(expr, env, loc)
     async def cmd_cycle (self, count:int=1) :
         """run one or more CPU cycle
          - count: number of cycles to run
@@ -437,8 +437,8 @@ class ShellRunner (Runner) :
                 start, stop = addr.split(":", 1)
             else :
                 start = stop = addr
-            start = int(start or "0", 16)
-            stop = int(stop or "FFFF", 16)
+            start = self.eval(start or "0")
+            stop = self.eval(stop or "FFFF")
             if start > stop :
                 raise ValueError
             return start, stop
@@ -460,19 +460,18 @@ class ShellRunner (Runner) :
     async def cmd_assert (self, expr:str, message:str=None) :
         """check assertion
          - expr: Python expression checked to be True, may include
-           - register names: the register's value
-           - intr: the interrupt vector as a list of 0/1
-           - mask: the interrupt mask (MR) as a list of 0/1
-           - clock: the clock counter
-           - screen: the text on screen (without colours)
-           - [ADDR]: the value in RAM at ADDR
-           - [ADDR:ADDR]: the list of values in RAM in specified range (inclusive)
+            - the names assigned with let
+            - registers names
+            - the interrupt vector INTR (list of 0/1)
+            - the interrupt mask MASK (list of 0/1)
+            - the clock tick counter CLOCK
+            - the memory RAM (list of ints)
+            - the screen text SCREEN
          - [message]: a message to be printed if assertion fails
         """
         global CLIRET
-        env = AssertEnv(self.ttc)
         try :
-            ret = eval(expr, env)
+            ret = self.eval(expr)
         except Exception as err :
             print(f"{F.RED}{S.BRIGHT}assert error:{S.RESET_ALL}"
                   f" {F.BLUE}{expr}{F.RESET} raised",
@@ -496,7 +495,11 @@ class ShellRunner (Runner) :
            - screen: text screen
         """
         for comp in component :
-            if (reg := comp.upper()) in regnum :
+            if comp in self.eval_env :
+                print(f"{F.GREEN}{comp}{F.RESET}"
+                      f" = {F.BLUE}{self.eval_env[comp]}"
+                      f"{S.RESET_ALL}")
+            elif (reg := comp.upper()) in regnum :
                 num = regnum[reg]
                 print(f"{F.GREEN}{reg}{F.RESET}"
                       f" = {F.BLUE}{_val(self.ttc.cpu.reg[num])}"