conversión de unidades con expresiones y con sentencias

lib/corpus.dart

@@ -85,7 +85,7 @@ class Corpus{
     return _allUnits.get(unit);
   }
 
-  String _converterFromCodeString(Number x, String codeString) {
+  String _converterFromCodeStringAsExpression(Number x, String codeString) {
     final buffer = StringBuffer();
     buffer.writeln("final x = ${x};");
     buffer.writeln("main(){return $codeString;}");
@@ -93,6 +93,14 @@ class Corpus{
     return code;
   }
 
+  String _converterFromCodeStringAsStatement(Number x, String codeString) {
+    final buffer = StringBuffer();
+    buffer.writeln("final x = ${x};");
+    buffer.writeln("main(){ $codeString; return x; }");
+    final code = buffer.toString();
+    return code;
+  }
+
   Number _convertToBase(Number x, String fromUnit) {
     final unit = getUnit(fromUnit);
 
@@ -104,9 +112,7 @@ class Corpus{
       throw ArgumentError("Unit has no codeFromUnitToBase: $unit");
     }
 
-    final d4rt = D4rt();
-    final completeSource = _converterFromCodeString(x, unit.codeFromUnitToBase as String);
-    final ret = d4rt.execute(source: completeSource);
+    final ret = _convertUsingCode(x, unit.codeFromUnitToBase as String);
     return ret as Number;
   }
 
@@ -121,12 +127,44 @@ class Corpus{
       throw ArgumentError("Unit has no codeFromBaseToUnit: $unit");
     }
 
-    final d4rt = D4rt();
-    final completeSource = _converterFromCodeString(x, unit.codeFromBaseToUnit as String);
-    final ret = d4rt.execute(source: completeSource);
+    final ret = _convertUsingCode(x, unit.codeFromBaseToUnit as String);
     return ret as Number;
   }
 
+
+  Number _convertUsingCode(Number x, String code ){
+    late String completeSourceExpression;
+    late String completeSourceStatement;
+    try {
+      completeSourceExpression = _converterFromCodeStringAsExpression(x, code);
+      final ret = _evaluate(completeSourceExpression);
+      return ret;
+    }
+    catch(e1,stack){
+      try{
+        completeSourceStatement = _converterFromCodeStringAsStatement(x, code);
+        final ret = _evaluate(completeSourceStatement);
+        return ret;
+      }
+      catch( e2, stack ){
+        print(completeSourceExpression);
+        print(e1);
+        print(completeSourceStatement);
+        print(e2);
+        throw FormulaEvaluationException( "Evaluation as statement and expression failed" );
+      }
+    }
+  }
+
+  static dynamic _evaluate(String code, [D4rt? interpreter]) {
+    final d4rtInterpreter = interpreter ?? FormulaEvaluator.createDefaultInterpreter();
+    FormulaEvaluator.prepareInterpreter(d4rtInterpreter);
+    final completeCode = "${FormulaEvaluator.d4rtImports}\n$code";
+    final result = d4rtInterpreter.execute(source: completeCode);
+    return result.toDouble();
+  }
+
+
   Number convert(Number x, String fromUnit, String toUnit) {
     final xBase = _convertToBase(x, fromUnit);
     final xTo = _convertFromBase(xBase, toUnit);

lib/defaults/units/temperature.d4rt.units

@@ -46,7 +46,7 @@
     "name": "Gas Mark",
     "symbol": "GM",
     "baseUnit": "Kelvin",
-    "toBase": """
+    "toBase": r"""
       if (x < 1) {
         double celsius = (243 - 25 * (log(1 / x) / log(2))) / 1.8;
         return celsius + 273.15; // convert Celsius to Kelvin

lib/formula_evaluator.dart

@@ -58,10 +58,9 @@ class FormulaEvaluator {
     interpreter.registerBridgedClass(myMathDefinition, "package:d4rt_formulas.dart");
   }
 
-
-  static dynamic evaluateExpression(String code) {
-    final interpreter = createDefaultInterpreter();
-    prepareInterpreter(interpreter);
+  static dynamic evaluateExpression(String code, [D4rt? interpreter]) {
+    final d4rtInterpreter = interpreter ?? createDefaultInterpreter();
+    prepareInterpreter(d4rtInterpreter);
     final d4rtCode = """
       import 'dart:math';
       import "package:d4rt_formulas.dart";
@@ -72,7 +71,7 @@ class FormulaEvaluator {
         return result;
       }""";
     //print("evaluateExpression:\n$d4rtCode");
-    final result = interpreter.execute(source: d4rtCode);
+    final result = d4rtInterpreter.execute(source: d4rtCode);
     return result.toDouble();
   }
   
@@ -112,19 +111,22 @@ class FormulaEvaluator {
     return formula.inputVarNames()..sort();
   }
 
+  static final String d4rtImports = """
+      import 'dart:math';
+      import "package:d4rt_formulas.dart";
+  """;
+
   String _buildCompleteSource(Formula formula, Map<String, dynamic> inputValues) {
     final buffer = StringBuffer();
 
     buffer.writeln("""
-      import 'dart:math';
-      import "package:d4rt_formulas.dart";
-
+      $d4rtImports
       
       main()
       {
       """
     );
-    
+
 
     for (final entry in inputValues.entries) {
       final varName = entry.key;