Abstract The Mixed‐Language Programming (MLP) System is a simple system that facilitates construction of sequential programs in which procedures can be written in different programming languages to exploit heterogeneity in language functionality. In addition, MLP provides a simple remote procedure call (RPC) facility that allows heterogeneity in machine functionality to be exploited. To minimize implementation cost, the system does not solve all of the problems related to mixed‐language programming; rather, MLP is designed to handle common situations well. Among the unique aspects of MLP are its advanced facilities, which allow complex situations to be handled with user intervention; for example, these facilities allow arguments of a type not defined by a language to be used by procedures written in that language. This paper overviews the use of MLP and describes its implementation. In addition, two programs that have been written using the MLP system—a small database system and a collection of plot routines—are discussed. The system executes on a collection of Vaxes and Suns running Berkeley UNIX. Currently supported languages are C, Pascal and Icon.

This paper describes the design of the Saguaro operating system for computers connected by a local-area network. Systems constructed on such an architecture have the potential advantages of concurrency and robustness. In Saguaro, these advantages are made available to the user through several mechanisms. One is channels, an interprocess communication and synchronization facility that allows the input and output of different commands to be connected to form general graphs of communicating processes. Two additional mechanisms are provided to support semitransparent file replication and access: reproduction sets and metafiles. A reproduction set is a collection of files that the system attempts to keep identical on a "best effort" basis. A metafile is a special file that contains symbolic pathnames of other files; when a metafile is opened, the system selects an available constituent file and opens it instead. The advantages of concurrency and robustness are also realized at the system level by the use of pools of server processes and decentralized allocation protocols. Saguaro also makes extensive use of a type system to describe user data such as files and to specify the types of arguments to commands and procedures. This enables the system to assist in type checking and leads to a user interface in which command-specific templates are available to facilitate command invocation.

An approach for facilitating mixed language programming in distributed systems is presented. It is based on adding a generic remote procedure call facility to each language, and the use of a type system to describe procedural interfaces, as well as data to be transferred between procedures. This type scheme also specifies a machine-independent representation for all data. By defining standard mappings for each programming language, the data conversions required for cross-langauge calls may be performed, automatically in most cases, by active agents that provide the interface between program components written in different languages. When necessary, explicit control of the conversation is possible. A prototype implementation of a system based on this approach has been constructed on a collection of machines running Berkeley UNIX®.