formula is more natural

README.md

@@ -10,9 +10,9 @@ If you are a contributor or an agent, please follow [CLAUDE.md](./CLAUDE.md) for
 
 # Formula file description
 
-The file is a json array of formulas.
+The file is a dart array of formulas. Each formula is a dart set literal
 
-```json
+```dart
 [
     {
         "name": "Newton's second law (scalar)",
@@ -29,10 +29,9 @@ The file is a json array of formulas.
                 "magnitude" : "Force"
             }
         },
-        "d4rt_code": "return m*a;"
+        "d4rt_code": "F = m*a;"
         
     }
-
 ]
 
 ```

lib/formula_evaluator.dart

@@ -49,7 +49,7 @@ class FormulaEvaluator {
       // Build the complete d4rt source code with variable declarations
       final completeSource = _buildCompleteSource(formula, inputValues);
       //print( "$formula");
-      //print( "$completeSource" );
+      print( "$completeSource" );
       
       // Execute the code using d4rt (no args needed since variables are in source)
       final result = _interpreter.execute(source: completeSource);
@@ -119,13 +119,12 @@ class FormulaEvaluator {
         buffer.writeln('var $varName = $value;');
       }
     }
-    
+    buffer.writeln("late var ${getOutputVariableName(formula)};");
-    // Add a blank line for readability
-    buffer.writeln();
     
     // Add the formula's d4rt code
-    buffer.write(formula.d4rtCode);
+    buffer.writeln(formula.d4rtCode);
-    buffer.write("}");
+    buffer.writeln("return ${getOutputVariableName(formula)};");
+    buffer.writeln("}");
     
     return buffer.toString();
   }

lib/formula_models.dart

@@ -64,6 +64,17 @@ class Formula {
   List<String> inputVarNames() =>
       input.map((v) => v.name).toList(growable: false);
 
+  factory Formula.fromStringLiteral( String setStringLiteral ){
+    var d4rt = D4rt();
+    final buffer = StringBuffer();
+    buffer.write( "main(){ return $setStringLiteral; }");
+    final code = buffer.toString();
+
+    final Map<Object?, Object?> setLiteral = d4rt.execute(source: code);
+
+    return Formula.fromSet(setLiteral);
+  }
+
   factory Formula.fromSet(Map<Object?, Object?> theSet) {
 
     Object safeGet(Map<Object?, Object?> map, String key){

test/formula_evaluator_test.dart

@@ -20,7 +20,7 @@ void main() {
           ],
           output: VariableSpec(name: 'F', magnitude: 'force'),
           d4rtCode: '''
-              return a * m;
+              F = a * m;
           ''',
         );
 
@@ -41,7 +41,7 @@ void main() {
           ],
           output: VariableSpec(name: 'result', magnitude: 'scalar'),
           d4rtCode: '''
-              return x + y;
+              result = x + y;
           ''',
         );
 
@@ -56,7 +56,7 @@ void main() {
           input: [VariableSpec(name: 'n', magnitude: 'scalar')],
           output: VariableSpec(name: 'result', magnitude: 'scalar'),
           d4rtCode: '''
-              return n * n;
+              result = n * n;
           ''',
         );
 
@@ -74,7 +74,7 @@ void main() {
           ],
           output: VariableSpec(name: 'discriminant', magnitude: 'scalar'),
           d4rtCode: '''
-              return b * b - 4 * a * c;
+              discriminant = b * b - 4 * a * c;
           ''',
         );
 
@@ -94,7 +94,7 @@ void main() {
             VariableSpec(name: 'b', magnitude: 'scalar'),
           ],
           output: VariableSpec(name: 'result', magnitude: 'scalar'),
-          d4rtCode: 'return a + b + z;',
+          d4rtCode: 'result = a + b + z;',
         );
 
         final order = evaluator.getInputVariableOrder(formula);
@@ -112,7 +112,7 @@ void main() {
           output: VariableSpec(name: 'result', magnitude: 'scalar'),
           d4rtCode: '''
               // Variables: a=1, y=2, z=3
-              return a * 100 + y * 10 + z;
+              result = a * 100 + y * 10 + z;
           ''',
         );
 
@@ -132,7 +132,7 @@ void main() {
             VariableSpec(name: 'y', magnitude: 'scalar'),
           ],
           output: VariableSpec(name: 'result', magnitude: 'scalar'),
-          d4rtCode: 'return x + y;',
+          d4rtCode: 'result = x + y;',
         );
 
         expect(
@@ -162,7 +162,7 @@ void main() {
           name: 'Test',
           input: [VariableSpec(name: 'x', magnitude: 'scalar')],
           output: VariableSpec(name: 'force', magnitude: 'Newton'),
-          d4rtCode: 'return x;',
+          d4rtCode: 'force = x;',
         );
 
         expect(evaluator.getOutputVariableName(formula), 'force');
@@ -175,7 +175,7 @@ void main() {
             name: 'Test',
             input: [VariableSpec(name: 'x', magnitude: 'scalar')],
             output: VariableSpec(name: 'force', magnitude: 'Newton'),
-            d4rtCode: 'return x;',
+            d4rtCode: 'force = x;',
           );
 
           expect(evaluator.getOutputVariableMagnitude(formula), 'Newton');
@@ -187,7 +187,7 @@ void main() {
           name: 'Valid Formula',
           input: [VariableSpec(name: 'x', magnitude: 'scalar')],
           output: VariableSpec(name: 'result', magnitude: 'Newton'),
-          d4rtCode: 'return x;',
+          d4rtCode: 'result = x;',
         );
 
         expect(evaluator.getOutputVariableName(validFormula), 'result');
@@ -202,7 +202,7 @@ void main() {
           name: 'Integer test',
           input: [VariableSpec(name: 'n', magnitude: 'count')],
           output: VariableSpec(name: 'result', magnitude: 'count'),
-          d4rtCode: 'return n + 1;',
+          d4rtCode: 'result = n + 1;',
         );
 
         final result = evaluator.evaluate(formula, {'n': 42});
@@ -214,7 +214,7 @@ void main() {
           name: 'Double test',
           input: [VariableSpec(name: 'x', magnitude: 'length')],
           output: VariableSpec(name: 'result', magnitude: 'area'),
-          d4rtCode: 'return x * x;',
+          d4rtCode: 'result = x * x;',
         );
 
         final result = evaluator.evaluate(formula, {'x': 3.14});

test/formula_models_test.dart

@@ -46,14 +46,7 @@ void main() {
     }    
     """;
 
-    var d4rt = D4rt();
+    final formula = Formula.fromStringLiteral(literal);
-    final buffer = StringBuffer();
-    buffer.write( "main(){ return $literal; }");
-    final code = buffer.toString();
-
-    final Map<Object?, Object?> setLiteral = d4rt.execute(source: code);
-
-    final formula = Formula.fromSet(setLiteral);
     final evaluator = FormulaEvaluator();
 
     final result = evaluator.evaluate(formula, {