Type: provide castFromBigRational conversion to Java data types

prism/src/parser/type/Type.java

@@ -26,6 +26,7 @@
 
 package parser.type;
 
+import param.BigRational;
 import prism.PrismLangException;
 
 public abstract class Type 
@@ -65,6 +66,20 @@ public abstract class Type
 		throw new PrismLangException("Cannot cast a value to type " + getTypeString());
 	}
 
+	/**
+	 * Cast a BigRational value to the Java data type (Boolean, Integer, Double, ...)
+	 * corresponding to this type.
+	 * <br>
+	 * For boolean and integer, this throws an exception if the value can not be
+	 * precisely represented by the Java data type; for double, loss of precision
+	 * is expected and does not raise an exception.
+	 */
+	public Object castFromBigRational(BigRational value) throws PrismLangException
+	{
+		// Play safe: assume error unless explicitly overridden.
+		throw new PrismLangException("Cannot cast rational number to type " + getTypeString());
+	}
+
 	@Override
 	public String toString()
 	{

prism/src/parser/type/TypeBool.java

@@ -26,6 +26,7 @@
 
 package parser.type;
 
+import param.BigRational;
 import prism.PrismLangException;
 
 public class TypeBool extends Type 
@@ -77,4 +78,11 @@ public class TypeBool extends Type
 		else
 			throw new PrismLangException("Can't convert " + value.getClass() + " to type " + getTypeString());
 	}
+
+	@Override
+	public Object castFromBigRational(BigRational value) throws PrismLangException
+	{
+		return value.toBoolean();
+	}
+
 }

prism/src/parser/type/TypeDouble.java

@@ -82,4 +82,11 @@ public class TypeDouble extends Type
 		else
 			throw new PrismLangException("Can't convert " + value.getClass() + " to type " + getTypeString());
 	}
+
+	@Override
+	public Object castFromBigRational(BigRational value) throws PrismLangException
+	{
+		return value.doubleValue();
+	}
+
 }

prism/src/parser/type/TypeInt.java

@@ -26,6 +26,7 @@
 
 package parser.type;
 
+import param.BigRational;
 import prism.PrismLangException;
 
 public class TypeInt extends Type 
@@ -77,4 +78,11 @@ public class TypeInt extends Type
 		else
 			throw new PrismLangException("Can't convert " + value.getClass() + " to type " + getTypeString());
 	}
+
+	@Override
+	public Object castFromBigRational(BigRational value) throws PrismLangException
+	{
+		return value.toInt();
+	}
+
 }