Refactor to improve iterations

- Use function abstractions (such as map, reduce, filter etc.) over
  for-of loops to gain benefits of having less side effects and easier
  readability.
- Enable `downLevelIterations` for writing modern code with lazy evaluation.
- Refactor for of loops to named abstractions to clearly express their
  intentions without needing to analyse the loop itself.
- Add missing cases for changes that had no tests.

tests/unit/application/Parser/Script/Compiler/Expressions/ExpressionsCompiler.spec.ts

@@ -151,6 +151,14 @@ describe('ExpressionsCompiler', () => {
             .withArgument('parameter2', 'value'),
           expectedError: 'parameter value(s) not provided for: "parameter1", "parameter3" but used in code',
         },
+        {
+          name: 'parameter names are not repeated in error message',
+          expressions: [
+            new ExpressionStub().withParameterNames(['parameter1', 'parameter1', 'parameter2', 'parameter2'], false),
+          ],
+          args: new FunctionCallArgumentCollectionStub(),
+          expectedError: 'parameter value(s) not provided for: "parameter1", "parameter2" but used in code',
+        },
       ];
       for (const testCase of testCases) {
         it(testCase.name, () => {

tests/unit/application/Parser/Script/Compiler/Expressions/Parser/Regex/RegexParser.spec.ts

@@ -31,6 +31,31 @@ describe('RegexParser', () => {
         });
       }
     });
+    it('throws when position is invalid', () => {
+      // arrange
+      const regexMatchingEmpty = /^/gm; /* expressions cannot be empty */
+      const code = 'unimportant';
+      const expectedErrorParts = [
+        `[${RegexParserConcrete.constructor.name}]`,
+        'invalid script position',
+        `Regex: ${regexMatchingEmpty}`,
+        `Code: ${code}`,
+      ];
+      const sut = new RegexParserConcrete(regexMatchingEmpty);
+      // act
+      let error: string;
+      try {
+        sut.findExpressions(code);
+      } catch (err) {
+        error = err.message;
+      }
+      // assert
+      expect(
+        expectedErrorParts.every((part) => error.includes(part)),
+        `Expected parts: ${expectedErrorParts.join(', ')}`
+          + `Actual error: ${error}`,
+      );
+    });
     describe('matches regex as expected', () => {
       // arrange
       const testCases = [

tests/unit/application/Parser/Script/Compiler/Function/Call/Compiler/FunctionCallCompiler.spec.ts

@@ -70,7 +70,7 @@ describe('FunctionCallCompiler', () => {
             },
             {
               name: 'provided: an unexpected parameter, when: none required',
-              functionParameters: undefined,
+              functionParameters: [],
               callParameters: ['unexpected-call-parameter'],
               expectedError:
                 `Function "${functionName}" has unexpected parameter(s) provided: "unexpected-call-parameter"`
@@ -90,10 +90,10 @@ describe('FunctionCallCompiler', () => {
               const func = new SharedFunctionStub(FunctionBodyType.Code)
                 .withName('test-function-name')
                 .withParameterNames(...testCase.functionParameters);
-              let params: FunctionCallParametersData = {};
-              for (const parameter of testCase.callParameters) {
-                params = { ...params, [parameter]: 'defined-parameter-value ' };
-              }
+              const params = testCase.callParameters
+                .reduce((result, parameter) => {
+                  return { ...result, [parameter]: 'defined-parameter-value ' };
+                }, {} as FunctionCallParametersData);
               const call = new FunctionCallStub()
                 .withFunctionName(func.name)
                 .withArguments(params);