Rework lib/strings.js functions using async/await pattern

js/processor/lib/strings.js

@@ -14,7 +14,7 @@ import { ProcessorErrorFactory } from '../error/processorErrorFactory';
 **/
 
 export function createSubstringFun () {
-  const substringFun = (sto, _) => {
+  const substringFun = async (sto, _) => {
     const str = sto.applyStore("str");
     const start = sto.applyStore("start");
     const end = sto.applyStore("end");
@@ -22,7 +22,7 @@ export function createSubstringFun () {
     const temp = new StoreValue(Types.STRING, result);
     sto.insertStore("$", temp);
     sto.mode = Modes.RETURN;
-    return Promise.resolve(sto);
+    return sto;
   };
 
   const block = new Commands.CommandBlock([],  [new Commands.SysCall(substringFun)]);
@@ -35,12 +35,12 @@ export function createSubstringFun () {
 }
 
 export function createLengthFun () {
-  const lengthFun = (sto, _) => {
+  const lengthFun = async (sto, _) => {
     const str = sto.applyStore("str");
     const temp = new StoreValue(Types.INTEGER, toInt(str.value.length));
     sto.insertStore("$", temp);
     sto.mode = Modes.RETURN;
-    return Promise.resolve(sto);
+    return sto;
   }
   const block = new Commands.CommandBlock([],  [new Commands.SysCall(lengthFun)]);
   const func = new Commands.Function('$length', Types.INTEGER,
@@ -50,12 +50,12 @@ export function createLengthFun () {
 }
 
 export function createUppercaseFun () {
-  const uppercaseFun = (sto, _) => {
+  const uppercaseFun = async (sto, _) => {
     const str = sto.applyStore("str");
     const temp = new StoreValue(Types.STRING, str.get().toUpperCase());
     sto.insertStore("$", temp);
     sto.mode = Modes.RETURN;
-    return Promise.resolve(sto);
+    return sto;
   }
   const block = new Commands.CommandBlock([],  [new Commands.SysCall(uppercaseFun)]);
   const func = new Commands.Function('$uppercase', Types.STRING,
@@ -65,12 +65,12 @@ export function createUppercaseFun () {
 }
 
 export function createLowercaseFun () {
-  const lowercaseFun = (sto, _) => {
+  const lowercaseFun = async (sto, _) => {
     const str = sto.applyStore("str");
     const temp = new StoreValue(Types.STRING, str.get().toLowerCase());
     sto.insertStore("$", temp);
     sto.mode = Modes.RETURN;
-    return Promise.resolve(sto);
+    return sto;
   }
   const block = new Commands.CommandBlock([],  [new Commands.SysCall(lowercaseFun)]);
   const func = new Commands.Function('$lowercase', Types.STRING,
@@ -80,16 +80,17 @@ export function createLowercaseFun () {
 }
 
 export function createrCharAtFun () {
-  const charAtFun = function (sto, _) {
+  const charAtFun = async function (sto, _) {
     const str = sto.applyStore("str");
     const idx = sto.applyStore("index");
     if (idx.get().toNumber() < 0 || idx.get().toNumber() >= str.get().length) {
-      return Promise.reject(ProcessorErrorFactory.invalid_string_index(idx.get().toNumber(), str.get(), this.function_call_stack.pop()));
+      throw ProcessorErrorFactory.invalid_string_index(idx.get().toNumber(), str.get(),
+        this.function_call_stack.pop());
     }
     const temp = new StoreValue(Types.STRING, str.get().charAt(idx.get().toNumber()));
     sto.insertStore("$", temp);
     sto.mode = Modes.RETURN;
-    return Promise.resolve(sto);
+    return sto;
   }
   const block = new Commands.CommandBlock([],  [new Commands.SysCall(charAtFun)]);
   const func = new Commands.Function('$charAt', Types.STRING,