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Mozart Interoperability

Examples

overview ________________________________

Stockhausen Operette 1 is based on Mozart and supports interoperability between Oz and Alice.

The Stockhausen compiler translates components into pickled Oz functors. It is possible to mix Oz and Alice code on a per-component basis. This document explains:

• how Alice data structures are mapped to Oz data structures
• how to import Oz functors into Alice components
• how to import Alice functors into Oz components

data representation _____________________

Basic Types

Values of basic types are mapped to corresponding Oz basic types. To support word operations, Mozart has been extended by a corresponding basic type.

Tuples and Records

Alice records are translated to Oz records by mapping all labels consisting only of digits to the corresponding integer feature, and all labels containing a letter to the corresponding atom feature.

Procedures

Conceptually, all Alice functions are unary. The typical idiom is to pass multiple arguments as a tuple of arguments. This case is treated specially by the Alice compiler.

Constructors

With a few exceptions simplifying interoperability, constructors of closed datatypes are mapped to atoms and constructors of open datatypes are mapped to names.

Constructed Values

Conceptually, all Alice constructors are unary. For interoperability, constructors syntactically declared taking a record as argument are treated as n-ary constructors.

For example, assuming a declaration

        datatype t1 = C1 of int * int

the Alice expression C1 (1, 2) evaluates to the Oz value 'C1'(1 2) due to the constructor C1 being binary. However, assuming the declaration

        datatype 'a t2 = C2 of 'a

the Alice expression C2 (1, 2) evaluates to the Oz value 'C2'(1#2) because the constructor C2 is unary.

Futures

Alice futures map directly to Oz transients. Promises are transparent on the Oz side.

Other Library Types

Some abstract library types are implemented natively:

Modules

Alice modules are translated to Oz data structures such:

Structure members are represented under record features. The feature names are computed as shown in the following table:

Signatures and types are not yet represented at run-time. Note that signature coercion is not performed operationally, that is, all structure members are visible on the Oz side.

Components

Alice components are translated into Oz functors:

The export of the generated functor is the record corresponding to the component considered as a single structure.

Exceptions

Alice exceptions are wrapped into alice(...) and raised as Oz error exceptions.

oz from alice ___________________________

Alice compiled components are annotated with signatures denoting the expected types of the component it imports and the actual type of the structure it computes. Compatibility of actual and expected signatures is checked at link-time to guarantee type safety. The actual export signature is also loaded at compile time to perform binding analysis and type-checking.

For this reason, export signatures must first be provided for Oz functors before they can be imported into Alice components. This will be shown by an example.

Assume the following Oz functor is stored at URL F.ozf:

        functor
        import
           System(show)
        export
           show: Show
        define
           fun {Show X} {System.show X} unit end
        end

To import this component into Alice, we would write a signature file F.sig containing:

        signature F_COMPONENT =
            sig
                val show: 'a -> unit
            end

The Oz functor F.ozf can now be combined with the signature at F.sig into a typed component TypedF.ozf by invoking the Stockhausen compiler thus:

        stoc --replacesign F.ozf F.sig TypedF.ozf

We can now import the component into Alice using an import announcement of the form

        import val show from "TypedF.ozf"

Note that the name of the signature is ignored.

If the signature does not truthfully describe the Oz component, run-time type exceptions will be raised.

alice from oz ___________________________

Since Oz does not type-check its imports at link-time, Alice components can be directly imported into Oz functors without conversion.

For example, assume the following Alice component is available at URL Example.ozf:

        structure Example =
            struct
                fun count f xs =
                    List.foldr (fn (x, n) =>
                                if f x then n + 1 else n) 0 xs
            end

An Oz functor could now import it as follows:

        functor
        import
            System(show)
            ExampleComponent('$Example': Example) at 'Example.ozf'
        define
            {System.show
             {{Example.count fun {$ X} X == 0 end} [1 0 2 0]}}
        end