make VAL robust to non-parseable inputs

Author: mhaupt

src/main/java/de/haupz/basicode/ast/ValNode.java

@@ -1,20 +1,25 @@
 package de.haupz.basicode.ast;
 
 import java.util.Optional;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
 /**
  * {@code VAL}.
  */
 public class ValNode extends WrappingExpressionNode {
 
+    private static final Pattern DOUBLE = Pattern.compile("^[-+]?[0-9]*\\.?[0-9]+([eE][-+]?[0-9]+)?");
+
     public ValNode(ExpressionNode expression) {
         super(expression);
     }
 
     @Override
     Optional<Object> evalWithTypes(Object value) {
         if (value instanceof String s) {
-            return Optional.of(Double.parseDouble(s));
+            Matcher matcher = DOUBLE.matcher(s);
+            return Optional.of(matcher.find() ? Double.parseDouble(matcher.group()) : 0.0);
         }
         return Optional.empty();
     }

src/test/java/de/haupz/basicode/MidsTest.java

@@ -57,4 +57,9 @@ public void testOmitLengthArgument() {
         testExpression("MID$(\"BASICODE\",8)", "E", String.class);
     }
 
+    @Test
+    public void testb64() {
+        testExpression("MID$(\"b64\",2,2)", "64", String.class);
+    }
+
 }

src/test/java/de/haupz/basicode/ValTest.java

@@ -19,9 +19,9 @@ public void testDouble() {
     }
 
     @Test
-    public void testError() {
-        testExpressionThrows("VAL(\"2+4\")", NumberFormatException.class);
-        testExpressionThrows("VAL(\"Hello\")", NumberFormatException.class);
+    public void testStrangeInput() {
+        testExpression("VAL(\"2+4\")", 2.0, Double.class);
+        testExpression("VAL(\"Hello\")", 0.0, Double.class);
     }
 
 }