nodes: introduce the concept of purity

IR of pure statements is not generated in Block node

compiler/nodes.py

@@ -48,7 +48,7 @@ class Node:
 
     def _pprint(self, depth: int | None, indent: str, _depth: int = 0) -> list[str]:
         if depth is not None and _depth >= depth:
-            return [f"{indent}{self.__class__.__name__} {{ ... }}"]
+            return [f"{indent}{self.__class__.__name__}(pure={self.pure}) {{ ... }}"]
 
         vals = self._values()
         try:
@@ -56,7 +56,7 @@ class Node:
         except TypeError:
             vals = (vals,)
 
-        result = [f"{self.__class__.__name__} {{"]
+        result = [f"{self.__class__.__name__}(pure={self.pure}) {{"]
         for val in vals:
             if isinstance(val, Node):
                 result += val._pprint(depth=depth, indent=indent, _depth=_depth + 1)
@@ -68,6 +68,10 @@ class Node:
 
         return result
 
+    @property
+    def pure(self) -> bool:
+        return all(v.pure for v in self._values())
+
     @abstractmethod
     def intermediate_representation(self) -> list[ir.IRItem]:
         raise OverrideMandatoryError()
@@ -97,6 +101,9 @@ class Literal(Node, ABC):
     def location(self) -> SourceLocation:
         return self.loc
 
+    def pure(self) -> bool:
+        return True
+
     def _values(self) -> list[Node | Any]:
         return [self.value]
 
@@ -274,6 +281,14 @@ class Block(Statement):
         super().__init__(*nodes)
         self.name = name
 
+    def intermediate_representation(self) -> list[ir.IRItem]:
+        result: list[ir.IRItem] = []
+        for node in self.nodes[:-1]:
+            if not node.pure:
+                result += node.intermediate_representation()
+        result += self.nodes[-1].intermediate_representation()
+        return result
+
     def semantic_analysis(self, context: semantic.Context | None):
         child_context = semantic.Context(name=self.name, parent=context)
         if context is not None: