ïmplement basic line expression substitutions

Author: josefalanga

tests/test_expressions.py

@@ -17,24 +17,18 @@
 
 
 def test_expressions1():
-    try:
-        runner1.resume()
+    expected_line = "Hello there Sam."
 
-        # the runner should throw an error
-        raise Exception(
-            "The runner ran without any issues. This test should fail. An Exception was expected.")
-    except Exception as e:
-        assert str(
-            e) == "Yarn stories with interpolated inline expressions are not yet supported."
+    runner1.resume()
+
+    actual_line = runner1.get_line()
+    assert actual_line == expected_line
 
 
 def test_expressions2():
-    try:
-        runner2.resume()
-
-        # the runner should throw an error
-        raise Exception(
-            "The runner ran without any issues. This test should fail. An Exception was expected.")
-    except Exception as e:
-        assert str(
-            e) == "Yarn stories with interpolated inline expressions are not yet supported."
+    expected_line = "Hello there Sam."
+
+    runner2.resume()
+
+    actual_line = runner2.get_line()
+    assert actual_line == expected_line

yarnrunner_python/runner.py

@@ -72,10 +72,13 @@ def __find_label(self, label_key):
                 f"The current node `{self.current_node}` does not have a label named `{label_key}")
 
     def __find_expressions(self, operand):
-        # TODO: implement this functionality
-        if int(operand.float_value) != 0:
-            raise Exception(
-                f"Yarn stories with interpolated inline expressions are not yet supported.")
+        params_amount = operand.float_value
+
+        params = []
+        while params_amount > 0:
+            params.insert(0, self._vm_data_stack.pop(0))
+            params_amount -= 1
+        return params
 
     def __debug_log(self, msg, **kwargs):
         if self._enable_tracing:
@@ -202,10 +205,9 @@ def __run_line(self, instruction):
 
         # if this instruction has a second operand, it's the number of expressions
         # on the line that need to be evaluated.
+        line_substitutions = []
         if len(instruction.operands) > 1:
-            line_substitutions = self.__find_expressions(
-                instruction.operands[1])
-            # TODO: implement substitutions
+            line_substitutions = self.__find_expressions(instruction.operands[1])
 
         if self._experimental_newlines:
             # attempt to add a newlines if the last thing we did was run a line
@@ -219,7 +221,13 @@ def __run_line(self, instruction):
                     for _i in range(diff - 1):
                         self._line_buffer.append('')
 
-        self._line_buffer.append(self.__lookup_string(string_key))
+        self._line_buffer.append(
+            self._make_line_substitutions(
+                self.__lookup_string(string_key), line_substitutions))
+        
+    @staticmethod
+    def _make_line_substitutions(line, substitutions):
+        return line.format(*substitutions)
 
     def __run_command(self, instruction):
         # split the command specifier by spaces, ignoring spaces
@@ -265,7 +273,6 @@ def __add_option(self, instruction):
         if len(instruction.operands) > 2:
             line_substitutions = self.__find_expressions(
                 instruction.operands[2])
-            # TODO: implement substitutions
 
         self._option_buffer.append({
             'index': len(self._option_buffer),