Add string function LEFT

Author: PetrPytelka

src/main/java/com/scriptbasic/utility/functions/StringFunctions.java

@@ -72,6 +72,20 @@ static public String rtrim(final String s) {
         return s.replaceAll("\\s*$", "");
     }
 
+    /**
+     * Return {@code len} number of characters from the left (the beginning) of the
+     * string.
+     *
+     * @param s   parameter
+     * @param len parameter
+     * @return return value
+     */
+    @BasicFunction(classification = {com.scriptbasic.classification.String.class,
+            com.scriptbasic.classification.Utility.class})
+    static public String left(final String s, final int len) {
+        return s.length() > len ? s.substring(0, len) : s;
+    }
+    
     /**
      * Return a substring from the string that starts at the position
      * {@code start} and has a length of {@code len}.

src/test/java/com/scriptbasic/testprograms/TestPrograms.java

@@ -160,6 +160,11 @@ public void testStringConcatenation() throws Exception {
         codeTest("TestStringConcatenation.bas", "");
     }
 
+    @Test
+    public void testStringFunctions() throws Exception {
+        codeTest("TestStringFunctions.bas", "0189");
+    }
+    
     @Test
     public void testJavaObjectFieldAccess() throws ScriptBasicException, ClassNotFoundException, AnalysisException {
         final var e = new TestingExecutor();

src/test/resources/com/scriptbasic/testprograms/TestStringFunctions.bas

@@ -0,0 +1,3 @@
+v = "0123456789"
+PRINT left(v,2)
+PRINT right(v,2)