PlusMinusExpr

Author: Eble

src/main/java/com/ExpressionEvaluatorMain.java

@@ -5,7 +5,7 @@ public class ExpressionEvaluatorMain {
     public static void main(String[] args) throws Exception {
         com.compiler.Lexer lexer = new com.compiler.Lexer();
         com.compiler.ExpressionEvaluator evaluator = new com.compiler.ExpressionEvaluator(lexer);
-        int result = evaluator.eval("4+5");
+        int result = evaluator.eval("4-5-3+2");
         System.out.println(result);
     }
 

src/main/java/com/compiler/ExpressionEvaluator.java

@@ -30,9 +30,23 @@ int getUnaryExpr() throws Exception {
     int getMulDivExpr() throws Exception {
         return getUnaryExpr();
     }
-
+   
     int getPlusMinusExpr() throws Exception {
+        // sumExpr: mulExpr (sumOp mulExpr)*
         int result = getMulDivExpr();
+        while (
+            m_lexer.lookAhead().m_type == TokenIntf.Type.PLUS ||
+            m_lexer.lookAhead().m_type == TokenIntf.Type.MINUS
+        ) {
+            TokenIntf.Type tokenType = m_lexer.lookAhead().m_type;
+            m_lexer.advance(); // getSumOp()
+            int op = getMulDivExpr();
+            if (tokenType == TokenIntf.Type.PLUS) {
+                result += op;
+            } else {
+                result -= op;
+            }
+        }
         return result;
     }
 

src/test/java/com/compiler/TestPlusMinusExpr.java

@@ -8,7 +8,7 @@ public class TestPlusMinusExpr extends TestExpressionEvaluatorBase {
 
     @Test
     public void testPlusMinusExpr() throws Exception {
-      assertEquals(5, evalExpression("5"));
+      assertEquals(5+42-19, evalExpression("5+42-19"));
     }
 
 }