Table of Contents
Abstract
The Melange interface generator provides a mechanism for providing access to native C code. It is modeled upon Apple Computer's Creole, and shares Creole's goals of automatically providing full support for a foreign interface based upon existing interface descriptions. It also, like Creole, provides mechanisms for explicitly adapting these interfaces to provide a greater match between C and Dylan data models.
Melange, however, differs from Creole in a number of significant ways. This document, therefore, provides a gentle introduction to Melange without attempting to build upon any existing descriptions of Creole.
Melange is an automatic interface generator which provides transparent access to both functions and data defined or generated by existing C libraries. It allows users to import "interfaces"[1] from existing C header files, controlled by the contents of a "define interface" top-level form which may be included in the same file as arbitrary Dylan code. The user may use the functions and data specified by this interface as if they were native Dylan objects, and may export them to other modules.
Melange provides reasonable interpretations for the various sorts of C declarations which may appear in a header file, as well as mechanisms for explicitly modifying the default interpretations when necessary. For example, users may:
specify rules for the translation of foreign names
explicitly specify new names for specific objects or routines
specify parameter passing conventions or mutability of foreign objects
specify mappings or equivalences between "foreign" data and native equivalents
choose to import only a subset of the declarations in the header file
All of these customizations, as well as the name of the C header file, are specified by a "define interface" clause. See the section called “A Concrete Example” for an example.
The basic model for interface importation is based upon that used within Apple Computer's "Creole" interface generator. There are, however, significant differences in some of the details. (For instance, the "equate", "map", and "object-file" directives used in the above example are unique to Melange. Likewise, Creole's "type" directive would not be accepted by Melange) You should, therefore, not expect Creole interface declarations to work within Melange without some modification.
[1] In fact, a C header file may contain arbitrary C code which Melange is unprepared to handle. By convention, however, ".h" files con tain only "interface declarations"—type declarations, function prototypes, global variable declarations, and "preprocessor constants." Since Melange can meaningfully process all of these, it is capable of handling the vast majority of header files which will be encountered in practice.