Refactor implementation of Tiger stdlib functions

hera/op.py

@@ -7,6 +7,7 @@
 from contextlib import suppress
 from typing import Dict, List, Optional
 
+from hera import stdlib
 from hera.data import Constant, DataLabel, Location, Messages, Token
 from hera.utils import format_int, from_u16, print_warning, to_u16, to_u32
 
@@ -936,13 +937,7 @@ class __EVAL(DebuggingOperation):
     P = (STRING,)
 
     def execute(self, vm):
-        # Rudimentary safeguard to make execution of malicious code harder. Users of
-        # hera-py should keep in mind that running arbitrary HERA code is no safer than
-        # running arbitrary code of any kind.
-        if "import" not in self.args[0]:
-            bytecode = compile(self.args[0], "<string>", "exec")
-            exec(bytecode, {}, {"vm": vm})
-
+        eval(self.args[0], {}, {"stdlib": stdlib, "vm": vm})
         vm.pc += 1
 
 

hera/stdlib.py

@@ -8,35 +8,72 @@
 """
 
 
+def tiger_printint_stack(vm):
+    print(vm.load_memory(vm.registers[14] + 3), end="")
+
+
+def tiger_print_stack(vm):
+    addr = vm.load_memory(vm.registers[14] + 3)
+    n = vm.load_memory(addr)
+    for i in range(n):
+        print(chr(vm.load_memory(addr + i + 1)), end="")
+
+
+def tiger_println_stack(vm):
+    addr = vm.load_memory(vm.registers[14] + 3)
+    n = vm.load_memory(addr)
+    for i in range(n):
+        print(chr(vm.load_memory(addr + i + 1)), end="")
+    print()
+
+
+def tiger_exit(vm):
+    vm.halted = True
+
+
+def tiger_div_stack(vm):
+    left = vm.load_memory(vm.registers[14] + 3)
+    right = vm.load_memory(vm.registers[14] + 4)
+    result = left // right if right != 0 else 0
+    vm.store_memory(vm.registers[14] + 3, result)
+
+
+def tiger_mod_stack(vm):
+    left = vm.load_memory(vm.registers[14] + 3)
+    right = vm.load_memory(vm.registers[14] + 4)
+    result = left % right if right != 0 else 0
+    vm.store_memory(vm.registers[14] + 3, result)
+
+
 # The standard library with parameters-on-the-stack functions.
 TIGER_STDLIB_STACK = """
 LABEL(printint)
-  __eval("print(vm.load_memory(vm.registers[14]+3), end='')")
+  __eval("stdlib.tiger_printint_stack(vm)")
   RETURN(FP_alt, PC_ret)
 
 
 LABEL(print)
-  __eval("addr = vm.load_memory(vm.registers[14]+3); n = vm.load_memory(addr)\\nfor i in range(n):\\n  print(chr(vm.load_memory(addr+i+1)), end='')")
+  __eval("stdlib.tiger_print_stack(vm)")
   RETURN(FP_alt, PC_ret)
 
 
 LABEL(println)
-  __eval("addr = vm.load_memory(vm.registers[14]+3); n = vm.load_memory(addr)\\nfor i in range(n):\\n  print(chr(vm.load_memory(addr+i+1)), end='')\\nprint()")
+  __eval("stdlib.tiger_println_stack(vm)")
   RETURN(FP_alt, PC_ret)
 
 
 LABEL(exit)
-  __eval("vm.pc = float('inf')")
+  __eval("stdlib.tiger_exit(vm)")
   RETURN(FP_alt, PC_ret)
 
 
 LABEL(div)
-  __eval("left = vm.load_memory(vm.registers[14]+3); right = vm.load_memory(vm.registers[14]+4); vm.store_memory(vm.registers[14]+3, left // right if right != 0 else 0)")
+  __eval("stdlib.tiger_div_stack(vm)")
   RETURN(FP_alt, PC_ret)
 
 
 LABEL(mod)
-  __eval("left = vm.load_memory(vm.registers[14]+3); right = vm.load_memory(vm.registers[14]+4); vm.store_memory(vm.registers[14]+3, left % right if right != 0 else 0)")
+  __eval("stdlib.tiger_mod_stack(vm)")
   RETURN(FP_alt, PC_ret)
 
 

test/test_exec/test_debug_ops.py

@@ -48,18 +48,12 @@ def test_println_increments_pc(vm):
 
 
 def test___eval(vm):
-    helper(vm, '__eval("vm.registers[7] = 10")')
+    helper(vm, '__eval("stdlib.tiger_exit(vm)")')
 
-    assert vm.registers[7] == 10
-
-
-def test___eval_cannot_import_anything(vm, capsys):
-    helper(vm, "__eval(\"import sys; sys.stdout.write('hi')\")")
-
-    assert capsys.readouterr().out == ""
+    assert vm.halted is True
 
 
 def test___eval_increments_pc(vm):
-    helper(vm, '__eval("")')
+    helper(vm, '__eval("0")')
 
     assert vm.pc == 1