I made a new release of Mint and DrJava with Mint yesterday: September 29, 2010 (r15858). The latest release is, as always, available from the Mint implementation page:
We have added the [cci lang=”java”]edu.rice.cs.mint.runtime.CodeFree[/cci] interface and the [cci lang=”java”]edu.rice.cs.mint.runtime.CheckedExceptionInCode[/cci] exception class.
The [cci lang=”java”]CodeFree[/cci] interface provides a different, more transparent way of specifying separable classes that can be used for non-local assignments and CSP. When a class is declared to implement the [cci lang=”java”]CodeFree[/cci] interface, the class is guaranteed to be code-free, provided a number of static checks are passed:
- All field types and method return types are code-free, either using the old definition that required the types to be [cci lang=”java”]final[/cci], or by themselves implementing the [cci lang=”java”]CodeFree[/cci] interface.
- The same applies to all subtypes of types implementing the [cci lang=”java”]CodeFree[/cci] interface. It is an error to extend a class declared to be code-free using the [cci lang=”java”]CodeFree[/cci] interface and then to add a field containing or a method returning code.
This new rule makes it simpler to work with non-primitive types since the classes do not have to be [cci lang=”java”]final[/cci] anymore. In the past, lifting had to be done instead of using CSP; that is not necessary anymore. Consider the old code with the required [cci lang=”java”]lift[/cci] method and its application instead of straight-forward CSP:
[cc lang=”java”]public abstract class Value {
public separable int intValue() { throw new WrongTypeException(); }
public separable boolean booleanValue() { throw new WrongTypeException(); }
public separable abstract boolean valueEq(Value other);
public separable abstract Code
}
public class IntValue extends Value {
private int _data;
// …
public separable Code
final int lfData = _data; // hack to help the Mint compiler
return <| (Value) new IntValue(lfData) |>;
}
}
public class BooleanValue extends Value {
private boolean _data;
// …
public separable Code
final boolean lfData = _data; // hack to help the Mint compiler
return <| (Value) new BooleanValue(lfData) |>;
}
}
// …
public class Val implements Exp {
private Code
public Val(final Value value) {
_value = value.lift(); // lifting here
}
// …
}[/cc]
and the new code that doesn’t require the [cci lang=”java”]lift[/cci] method anymore:
[cc lang=”java”]public abstract class Value implements CodeFree, Serializable {
public separable int intValue() { throw new WrongTypeException(); }
public separable boolean booleanValue() { throw new WrongTypeException(); }
public separable abstract boolean valueEq(Value other);
}
public class IntValue extends Value {
private int _data;
// …
}
public class BooleanValue extends Value {
private boolean _data;
// …
}
// …
public class Val implements Exp {
private Code
public Val(final Value value) {
_value = <| value |>; // straight-forward CSP
}
// …
}
[/cc]
Please note that a class used in CSP still needs to be serializable if the code object it is used in is to be saved using [cci lang=”java”]MintSerializer.save[/cci]. That means that whenever you implement [cci lang=”java”]CodeFree[/cci], you should consider also implementing the [cci lang=”java”]java.io.Serializable[/cci] interface.
The second change involves the way checked exceptions are thrown inside a code object. In the past, checked exceptions were not allowed, because the [cci lang=”java”]Code.run()[/cci] method did not have a [cci lang=”java”]throws Throwable[/cci] clause.
We still didn’t add such a clause, because it would essentially require a try-catch construct around every call to [cci lang=”java”]Code.run()[/cci]. Instead, checked exceptions are caught and rethrown wrapped in a [cci lang=”java”]edu.rice.cs.mint.runtime.CheckedExceptionInCode[/cci] unchecked exception. Here is an example:
[cc lang=”java”]public static separable void m() throws IOException {
new File(“/this/is/a/bad/path”).createNewFile(); // throws IOException
}
// …
SafeCode
try {
c.run();
}
catch(CheckedExceptionInCode ce) {
Throwable cause = ce.getCause();
// …
}[/cc]
We also improved error checking for calls to separable methods and fixed a bug that required [cci lang=”java”]SafeCode
The version of DrJava with Mint is based on the current trunk (and therefore is newer than the updated stable release of DrJava that was recently made available).
(Re-posted from The Java Mint Blog.)
