Create evaluator for sum (sum, subtraction and string concatenation)

smnp/runtime/evaluators/sum.py

@@ -0,0 +1,40 @@
+from smnp.error.runtime import RuntimeException
+from smnp.runtime.evaluator import Evaluator
+from smnp.runtime.evaluators.expression import expressionEvaluator
+from smnp.type.model import Type
+
+
+class SumEvaluator(Evaluator):
+
+    @classmethod
+    def evaluator(cls, node, environment):
+        left = expressionEvaluator(doAssert=True)(node.left, environment).value
+        right = expressionEvaluator(doAssert=True)(node.right, environment).value
+
+        if left.type == right.type == Type.INTEGER:
+            return cls.integerEvaluator(left, node.operator, right)
+
+        if left.type == right.type == Type.STRING:
+            return cls.stringEvaluator(left, node.operator, right)
+
+        raise RuntimeException(f"Operator {node.operator.value} is not supported by {left.type.name.lower()} and {right.type.name.lower()} types", node.operator.pos)
+
+    @classmethod
+    def integerEvaluator(cls, left, operator, right):
+        if operator.value == "+":
+            return Type.integer(left.value + right.value)
+
+        if operator.value == "-":
+            return Type.integer(left.value - right.value)
+
+        raise RuntimeError("This line should never be reached")
+
+    @classmethod
+    def stringEvaluator(cls, left, operator, right):
+        if operator.value == "+":
+            return Type.string(left.value + right.value)
+
+        if operator.value == "-":
+            raise RuntimeException(f"Operator {operator.value} is not supported by string types", operator.pos)
+
+        raise RuntimeError("This line should never be reached")