diff --git a/lib/defaults/formulas.d4rt b/assets/formulas/formulas.d4rt
similarity index 100%
rename from lib/defaults/formulas.d4rt
rename to assets/formulas/formulas.d4rt
diff --git a/lib/defaults/units/angle.d4rt.units b/assets/units/angle.d4rt.units
similarity index 100%
rename from lib/defaults/units/angle.d4rt.units
rename to assets/units/angle.d4rt.units
diff --git a/lib/defaults/units/area.d4rt.units b/assets/units/area.d4rt.units
similarity index 100%
rename from lib/defaults/units/area.d4rt.units
rename to assets/units/area.d4rt.units
diff --git a/lib/defaults/units/distance.d4rt.units b/assets/units/distance.d4rt.units
similarity index 100%
rename from lib/defaults/units/distance.d4rt.units
rename to assets/units/distance.d4rt.units
diff --git a/lib/defaults/units/energy.d4rt.units b/assets/units/energy.d4rt.units
similarity index 100%
rename from lib/defaults/units/energy.d4rt.units
rename to assets/units/energy.d4rt.units
diff --git a/lib/defaults/units/force.d4rt.units b/assets/units/force.d4rt.units
similarity index 100%
rename from lib/defaults/units/force.d4rt.units
rename to assets/units/force.d4rt.units
diff --git a/lib/defaults/units/mass.d4rt.units b/assets/units/mass.d4rt.units
similarity index 100%
rename from lib/defaults/units/mass.d4rt.units
rename to assets/units/mass.d4rt.units
diff --git a/lib/defaults/units/pressure.d4rt.units b/assets/units/pressure.d4rt.units
similarity index 100%
rename from lib/defaults/units/pressure.d4rt.units
rename to assets/units/pressure.d4rt.units
diff --git a/assets/units/scalar.d4rt.units b/assets/units/scalar.d4rt.units
new file mode 100644
index 0000000..0533d87
--- /dev/null
+++ b/assets/units/scalar.d4rt.units
@@ -0,0 +1,3 @@
+[
+  {"name": "scalar", "symbol": "", "isBase": true},
+]
\ No newline at end of file
diff --git a/lib/defaults/units/temperature.d4rt.units b/assets/units/temperature.d4rt.units
similarity index 100%
rename from lib/defaults/units/temperature.d4rt.units
rename to assets/units/temperature.d4rt.units
diff --git a/lib/defaults/units/time.d4rt.units b/assets/units/time.d4rt.units
similarity index 100%
rename from lib/defaults/units/time.d4rt.units
rename to assets/units/time.d4rt.units
diff --git a/lib/defaults/units/velocity.d4rt.units b/assets/units/velocity.d4rt.units
similarity index 100%
rename from lib/defaults/units/velocity.d4rt.units
rename to assets/units/velocity.d4rt.units
diff --git a/lib/ai/formula_screen.dart b/lib/ai/formula_screen.dart
index 7b12262..4039f5a 100644
--- a/lib/ai/formula_screen.dart
+++ b/lib/ai/formula_screen.dart
@@ -1,6 +1,4 @@
-
 import 'package:flutter/material.dart';
-import 'package:flutter/services.dart';
 import 'package:flutter_markdown/flutter_markdown.dart';
 import '../formula_models.dart';
 import '../formula_evaluator.dart';
@@ -11,11 +9,7 @@ class FormulaScreen extends StatefulWidget {
   final Formula formula;
   final Corpus corpus;
 
-  const FormulaScreen({
-    super.key,
-    required this.formula,
-    required this.corpus,
-  });
+  const FormulaScreen({super.key, required this.formula, required this.corpus});
 
   @override
   State<FormulaScreen> createState() => _FormulaScreenState();
@@ -24,7 +18,7 @@ class FormulaScreen extends StatefulWidget {
 //// Start of D4rtEditingController class ////
 class D4rtEditingController extends TextEditingController {
   String? _lastError;
-
+  String _text = "";
   String? get lastError => _lastError;
   FormulaResult? _lastValue;
 
@@ -46,7 +40,6 @@ class D4rtEditingController extends TextEditingController {
 
   get d4rtValue => _lastValue;
 
-  @override
   set text(String newText) {
     super.text = newText;
     validate();
@@ -97,27 +90,37 @@ class _FormulaScreenState extends State<FormulaScreen> {
       final inputValues = <String, dynamic>{};
       for (final input in widget.formula.input) {
         final controller = _inputControllers[input.name]!;
-        if( controller.d4rtValue == null ){
-          throw FormulaEvaluationException( "Field ${input.name} is invalid" );
+        if (controller.d4rtValue == null) {
+          //throw FormulaEvaluationException("Field ${input.name} is invalid");
+          _result = "";
+          return;
         }
-        final value = controller.d4rtValue.value;
 
-        // Convert input to base unit if needed
-        // Always convert from dropdown unit to variable's base unit
-        late final convertedValue;
-        if( value is Number && input.unit != null ) {
-          convertedValue = widget.corpus.convert(
-            value,
-            _selectedUnits[input.name]!,
-            input.unit as String,
-          );
-        }
-        else{
-          convertedValue = value;
+        late final dynamic convertedValue;
+
+        switch (controller.d4rtValue) {
+          case NumberResult nr:
+            // Convert input to base unit if needed
+            // Always convert from dropdown unit to variable's base unit
+            if (input.unit != null) {
+              convertedValue = widget.corpus.convert(
+                nr.value,
+                _selectedUnits[input.name]!,
+                input.unit as String,
+              );
+            } else {
+              convertedValue = nr.value;
+            }
+
+          case StringResult sr:
+            convertedValue = sr.value;
+          default:
+            throw FormulaEvaluationException(
+              "Field ${input.name} has unsupported type ${controller.d4rtValue!.runtimeType}",
+            );
         }
 
         inputValues[input.name] = convertedValue;
-
       }
 
       final evaluator = FormulaEvaluator();
@@ -125,14 +128,11 @@ class _FormulaScreenState extends State<FormulaScreen> {
 
       // Convert output to selected unit if needed
       String? unit = widget.formula.output.unit;
-      if( unit != null ) {
-        _result = widget.corpus.convert(
-          result,
-          unit,
-          _selectedOutputUnit!,
-        ).toStringAsFixed(2);
-      }
-      else{
+      if (unit != null) {
+        _result = widget.corpus
+            .convert(result, unit, _selectedOutputUnit!)
+            .toStringAsFixed(2);
+      } else {
         _result = result;
       }
 
@@ -142,7 +142,7 @@ class _FormulaScreenState extends State<FormulaScreen> {
     } catch (e, stack) {
       debugPrint('Formula evaluation error: $e');
       debugPrint('Stack trace: $stack');
-      
+
       ScaffoldMessenger.of(context).showSnackBar(
         SnackBar(
           content: Text('Error: ${e.toString()}\n${stack.toString()}'),
@@ -155,9 +155,7 @@ class _FormulaScreenState extends State<FormulaScreen> {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      appBar: AppBar(
-        title: Text(widget.formula.name),
-      ),
+      appBar: AppBar(title: Text(widget.formula.name)),
       body: Form(
         key: _formKey,
         child: Padding(
@@ -176,7 +174,7 @@ class _FormulaScreenState extends State<FormulaScreen> {
   }
 
   Widget _buildDescriptionSection() {
-    if (widget.formula.description == null || 
+    if (widget.formula.description == null ||
         widget.formula.description!.isEmpty) {
       return const SizedBox.shrink();
     }
@@ -186,9 +184,9 @@ class _FormulaScreenState extends State<FormulaScreen> {
       children: [
         Text(
           'Description',
-          style: Theme.of(context).textTheme.titleMedium?.copyWith(
-            fontWeight: FontWeight.bold,
-          ),
+          style: Theme.of(
+            context,
+          ).textTheme.titleMedium?.copyWith(fontWeight: FontWeight.bold),
         ),
         const SizedBox(height: 8),
         Container(
@@ -213,9 +211,9 @@ class _FormulaScreenState extends State<FormulaScreen> {
       children: [
         Text(
           'Input Variables',
-          style: Theme.of(context).textTheme.titleMedium?.copyWith(
-            fontWeight: FontWeight.bold,
-          ),
+          style: Theme.of(
+            context,
+          ).textTheme.titleMedium?.copyWith(fontWeight: FontWeight.bold),
         ),
         const SizedBox(height: 8),
         ...widget.formula.input.map((variable) => _buildVariableRow(variable)),
@@ -229,9 +227,9 @@ class _FormulaScreenState extends State<FormulaScreen> {
       children: [
         Text(
           'Result',
-          style: Theme.of(context).textTheme.titleMedium?.copyWith(
-            fontWeight: FontWeight.bold,
-          ),
+          style: Theme.of(
+            context,
+          ).textTheme.titleMedium?.copyWith(fontWeight: FontWeight.bold),
         ),
         const SizedBox(height: 8),
         Row(
@@ -286,6 +284,7 @@ class _FormulaScreenState extends State<FormulaScreen> {
               decoration: const InputDecoration(
                 border: UnderlineInputBorder(),
               ),
+              autovalidateMode: AutovalidateMode.always,
               validator: (value) {
                 if (value == null || value.isEmpty) {
                   return 'Required';
diff --git a/lib/corpus.dart b/lib/corpus.dart
index 0710d8b..f6b37e9 100644
--- a/lib/corpus.dart
+++ b/lib/corpus.dart
@@ -73,7 +73,7 @@ class Corpus{
 
   List<String> unitsOfSameMagnitude(String? unit){
     if( unit == null ){
-      return ["unitless"];
+      return ["scalar"];
     }
     final base = getUnit(unit).baseUnit;
     return _baseToUnits[base] as List<String>;
@@ -90,7 +90,7 @@ class Corpus{
 
   String _converterFromCodeStringAsExpression(Number x, String codeString) {
     final buffer = StringBuffer();
-    buffer.writeln("final x = ${x};");
+    buffer.writeln("final x = $x;");
     buffer.writeln("main(){return $codeString;}");
     final code = buffer.toString();
     return code;
@@ -98,7 +98,7 @@ class Corpus{
 
   String _converterFromCodeStringAsStatement(Number x, String codeString) {
     final buffer = StringBuffer();
-    buffer.writeln("final x = ${x};");
+    buffer.writeln("final x = $x;");
     buffer.writeln("main(){ $codeString; return x; }");
     final code = buffer.toString();
     return code;
diff --git a/lib/defaults/default_corpus.dart b/lib/defaults/default_corpus.dart
index d740ba8..af7f983 100644
--- a/lib/defaults/default_corpus.dart
+++ b/lib/defaults/default_corpus.dart
@@ -1,42 +1,48 @@
+import 'dart:async';
 import 'dart:convert' show utf8;
+import 'package:flutter/services.dart' show rootBundle;
 
 import 'package:resource_portable/resource_portable.dart' show Resource;
 
 import '../corpus.dart';
 import '../formula_models.dart';
 
+
 Future<Corpus> createDefaultCorpus() async{
   final corpus = Corpus();
 
+  Future<String> loadResourceAsString(String path) async {
+    return await rootBundle.loadString(path, cache: false);
+  }
+
+
   Future<void> loadUnits() async {
     final unitResources = [
-      "lib/defaults/units/angle.d4rt.units",
-      "lib/defaults/units/area.d4rt.units",
-      "lib/defaults/units/distance.d4rt.units",
-      "lib/defaults/units/energy.d4rt.units",
-      "lib/defaults/units/force.d4rt.units",
-      "lib/defaults/units/mass.d4rt.units",
-      "lib/defaults/units/pressure.d4rt.units",
-      "lib/defaults/units/scalar.d4rt.units",
-      "lib/defaults/units/temperature.d4rt.units",
-      "lib/defaults/units/time.d4rt.units",
-      "lib/defaults/units/velocity.d4rt.units",
+      "assets/units/angle.d4rt.units",
+      "assets/units/area.d4rt.units",
+      "assets/units/distance.d4rt.units",
+      "assets/units/energy.d4rt.units",
+      "assets/units/force.d4rt.units",
+      "assets/units/mass.d4rt.units",
+      "assets/units/pressure.d4rt.units",
+      "assets/units/scalar.d4rt.units",
+      "assets/units/temperature.d4rt.units",
+      "assets/units/time.d4rt.units",
+      "assets/units/velocity.d4rt.units",
     ];
 
     for (final unitRes in unitResources) {
-      final resource = Resource(unitRes);
-      final literal = await resource.readAsString(encoding: utf8);
+      final literal = await loadResourceAsString(unitRes);
       final units = UnitSpec.fromArrayStringLiteral(literal);
       corpus.loadUnits(units);
     }
   }
 
   Future<void> loadFormulas() async {
-    final formulaResources = ["lib/defaults/formulas.d4rt"];
+    final formulaResources = ["assets/formulas/formulas.d4rt"];
 
     for (final formRes in formulaResources) {
-      final resource = Resource(formRes);
-      final literal = await resource.readAsString(encoding: utf8);
+      final literal = await loadResourceAsString(formRes);
       final formulas = Formula.fromArrayStringLiteral(literal);
       corpus.loadFormulas(formulas);
     }
diff --git a/lib/defaults/units/scalar.d4rt.units b/lib/defaults/units/scalar.d4rt.units
deleted file mode 100644
index c314f66..0000000
--- a/lib/defaults/units/scalar.d4rt.units
+++ /dev/null
@@ -1,3 +0,0 @@
-[
-  {"name": "scalar", "symbol": "", "isBase": true}
-]
\ No newline at end of file
diff --git a/lib/formula_evaluator.dart b/lib/formula_evaluator.dart
index 9a844b9..1f6d961 100644
--- a/lib/formula_evaluator.dart
+++ b/lib/formula_evaluator.dart
@@ -76,14 +76,14 @@ class FormulaEvaluator {
     final d4rtInterpreter = interpreter ?? createDefaultInterpreter();
     prepareInterpreter(d4rtInterpreter);
     final d4rtCode = """
-      ${d4rtImports}
+      $d4rtImports
       main()
       {
         late var result;
         result = $code;
         return result;
       }""";
-    //print("evaluateExpression:\n$d4rtCode");
+    print("evaluateExpression:\n$d4rtCode");
     final result = d4rtInterpreter.execute(source: d4rtCode);
     switch ( result ){
       case int value:
diff --git a/lib/formula_models.dart b/lib/formula_models.dart
index 05bb6a8..9a0c5f6 100644
--- a/lib/formula_models.dart
+++ b/lib/formula_models.dart
@@ -102,17 +102,17 @@ class UnitSpec {
 class VariableSpec {
   final String name;
   final String? unit;
-  final List<dynamic>? allowedValues;
+  final List<dynamic>? values;
 
-  VariableSpec({required this.name, this.unit, this.allowedValues}){
-    final valuesValid = allowedValues != null && allowedValues?.isNotEmpty == true;
+  VariableSpec({required this.name, this.unit, this.values}){
+    final valuesValid = values != null && values?.isNotEmpty == true;
     if( unit == null && !valuesValid ){
-      throw new ArgumentError("$name: at least unit or allowedValues should be valid");
+      throw ArgumentError("$name: at least unit or allowedValues should be valid");
     }
   }
 
   @override
-  String toString() => 'var($name: $unit${allowedValues != null ? ' allowed: $allowedValues' : ''})';
+  String toString() => 'var($name: $unit${values != null ? ' allowed: $values' : ''})';
 
   @override
   bool operator ==(Object other) =>
@@ -121,10 +121,10 @@ class VariableSpec {
           runtimeType == other.runtimeType &&
           unit == other.unit &&
           name == other.name &&
-          const DeepCollectionEquality().equals(allowedValues, other.allowedValues);
+          const DeepCollectionEquality().equals(values, other.values);
 
   @override
-  int get hashCode => Object.hash(unit, name, allowedValues != null ? const DeepCollectionEquality().hash(allowedValues!) : 0);
+  int get hashCode => Object.hash(unit, name, values != null ? const DeepCollectionEquality().hash(values!) : 0);
 }
 
 class Formula {
@@ -146,7 +146,7 @@ class Formula {
     validate();
   }
 
-  validate() {
+  void validate() {
     if (name.trim().isEmpty) {
       throw ArgumentError('Formula name cannot be empty');
     }
@@ -220,7 +220,7 @@ class Formula {
       return VariableSpec(
         name: name,
         unit: unit,
-        allowedValues: allowed?.toList(growable: false),
+        values: allowed?.toList(growable: false),
       );
     }
 
diff --git a/lib/main.dart b/lib/main.dart
index f21f76c..0f44288 100644
--- a/lib/main.dart
+++ b/lib/main.dart
@@ -6,6 +6,7 @@ import 'corpus.dart';
 import 'defaults/default_corpus.dart';
 
 void main() {
+  WidgetsFlutterBinding.ensureInitialized();
   runApp(MaterialApp(
     home: FutureBuilder<Corpus>(
       future: createDefaultCorpus(),
diff --git a/pubspec.yaml b/pubspec.yaml
index 7a0cea1..c143b38 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -68,6 +68,9 @@ flutter:
   # assets:
   #   - images/a_dot_burr.jpeg
   #   - images/a_dot_ham.jpeg
+  assets:
+    - assets/units/
+    - assets/formulas/
 
   # An image asset can refer to one or more resolution-specific "variants", see
   # https://flutter.dev/to/resolution-aware-images
diff --git a/test/d4rt_test.dart b/test/d4rt_test.dart
index db0aeb4..0e948a8 100644
--- a/test/d4rt_test.dart
+++ b/test/d4rt_test.dart
@@ -3,7 +3,7 @@ import 'package:d4rt/d4rt.dart';
 import 'dart:math' as Math;
 
 
-main(){
+void main(){
   test('Access to Math', () {
 
       final completeSource = """
diff --git a/test/dart_test.dart b/test/dart_test.dart
index 9777d46..9e78acc 100644
--- a/test/dart_test.dart
+++ b/test/dart_test.dart
@@ -3,7 +3,7 @@ import 'package:d4rt/d4rt.dart';
 import 'dart:math' as Math;
 
 
-main(){
+void main(){
   test('for dart grammar tests', () {
 
   });
diff --git a/test/formula_evaluator_test.dart b/test/formula_evaluator_test.dart
index 0b4c04d..7c553ce 100644
--- a/test/formula_evaluator_test.dart
+++ b/test/formula_evaluator_test.dart
@@ -208,5 +208,112 @@ void main() {
         expect(result, closeTo(9.8596, 0.0001));
       });
     });
+
+    group('APGAR Score', () {
+      test('evaluates APGAR score formula - Normal case', () {
+        final formula = Formula(
+          name: "Apgar Score",
+          description: "Newborn health assessment scoring system",
+          input: [
+            VariableSpec(name: "HeartRate", values: ["hr1", "hr2", "hr3"]),
+            VariableSpec(name: "Breathing", values: ["hr1", "hr2", "hr3"]),
+            VariableSpec(name: "MuscleTone", values: ["hr1", "hr2", "hr3"]),
+            VariableSpec(name: "Reflexes", values: ["hr1", "hr2", "hr3"]),
+            VariableSpec(name: "SkinColor", values: ["hr1", "hr2", "hr3"])
+          ],
+          output: VariableSpec(name: "Result", unit: "stringscalar"),
+          d4rtCode: """
+            var total = HeartRate + Breathing + MuscleTone + Reflexes + SkinColor;
+            var interpretation = switch (total) {
+              >= 7 => 'Normal',
+              4-6 => 'Requires attention',
+              _ => 'Emergency care needed'
+            };
+            Result = 'Score: \$total - \$interpretation';
+          """,
+        );
+
+        // Test normal case (score 7-10)
+        final result = evaluator.evaluate(formula, {
+          'HeartRate': 2,
+          'Breathing': 2,
+          'MuscleTone': 2,
+          'Reflexes': 2,
+          'SkinColor': 2
+        });
+
+        expect(result, 'Score: 10 - Normal');
+      });
+
+      test('evaluates APGAR score formula - Requires attention case', () {
+        final formula = Formula(
+          name: "Apgar Score",
+          description: "Newborn health assessment scoring system",
+          input: [
+            VariableSpec(name: "HeartRate", values: ["hr1", "hr2", "hr3"]),
+            VariableSpec(name: "Breathing", values: ["hr1", "hr2", "hr3"]),
+            VariableSpec(name: "MuscleTone", values: ["hr1", "hr2", "hr3"]),
+            VariableSpec(name: "Reflexes", values: ["hr1", "hr2", "hr3"]),
+            VariableSpec(name: "SkinColor", values: ["hr1", "hr2", "hr3"])
+          ],
+          output: VariableSpec(name: "Result", unit: "stringscalar"),
+          d4rtCode: """
+            var total = HeartRate + Breathing + MuscleTone + Reflexes + SkinColor;
+            var interpretation = switch (total) {
+              >= 7 => 'Normal',
+              4-6 => 'Requires attention',
+              _ => 'Emergency care needed'
+            };
+            Result = 'Score: \$total - \$interpretation';
+          """,
+        );
+
+        // Test requires attention case (score 4-6)
+        final result = evaluator.evaluate(formula, {
+          'HeartRate': 1,
+          'Breathing': 1,
+          'MuscleTone': 1,
+          'Reflexes': 1,
+          'SkinColor': 2
+        });
+
+        expect(result, 'Score: 6 - Requires attention');
+      });
+
+      test('evaluates APGAR score formula - Emergency case', () {
+        final formula = Formula(
+          name: "Apgar Score",
+          description: "Newborn health assessment scoring system",
+          input: [
+            VariableSpec(name: "HeartRate", values: ["hr1", "hr2", "hr3"]),
+            VariableSpec(name: "Breathing", values: ["hr1", "hr2", "hr3"]),
+            VariableSpec(name: "MuscleTone", values: ["hr1", "hr2", "hr3"]),
+            VariableSpec(name: "Reflexes", values: ["hr1", "hr2", "hr3"]),
+            VariableSpec(name: "SkinColor", values: ["hr1", "hr2", "hr3"])
+          ],
+          output: VariableSpec(name: "Result", unit: "stringscalar"),
+          d4rtCode: """
+            var total = HeartRate + Breathing + MuscleTone + Reflexes + SkinColor;
+            var interpretation = switch (total) {
+              >= 7 => 'Normal',
+              4-6 => 'Requires attention',
+              _ => 'Emergency care needed'
+            };
+            Result = 'Score: \$total - \$interpretation';
+          """,
+        );
+
+        // Test emergency case (score 0-3)
+        final result = evaluator.evaluate(formula, {
+          'HeartRate': 0,
+          'Breathing': 0,
+          'MuscleTone': 1,
+          'Reflexes': 0,
+          'SkinColor': 1
+        });
+
+        expect(result, 'Score: 2 - Emergency care needed');
+      });
+    });
   });
 }