xerox 19771017 Mesa 3.0 Compiler Update Mesa Language Changes free download

File name 19771017_Mesa_3.0_Compiler_Update_Mesa_Language_Changes.pdf

Inter-Office Memorandum To Mesa Users Date October 17, 1977 From Ed Satterthwaite Location Palo Alto Subject Mesa 3.0 Compiler Update Organization CSL Mesa Language Changes XEROX Filed on: [MAXC]MESACOMPILER30.8RAVO This release of the Mesa compiler introduces several changes of interest or importance to all Mesa programmers. A number of changes in the language have been made. Some of these will calise programs acceptable to previolls compilers to be rejected unless those programs are modified. The reasons for maki ng sllch changes are the following: To support new ways of describing configurations and binding them together. To add new facilities to the language. To prepare for certain language extensions that are now fairly well understood and for which preliminary designs exist. Language Changes Related to the Binder Overview The following overview might be helpful in understanding the changes related to the new binder. See the release summary for further references. The binder produces a configuration, which is a collection of module instances. Each module instance is represented by a global frame. Resolution of intermodular references is based upon copying descriptor and pointer values from well-defined interfaces into these global frames. More precisely, the binder produces configuration descriptions, which must be "relocated" by the loader to produce an actual configuration. There are two kinds of modules: DEFINITIONS and PROGRAM. The text of either kind implicitly defines a type. In the case of a program module X, this is a frame type, denoted by FRAME[X]. Values of this type are created in the (frame) heap, either by loading or by the NEW operation. They cannot be embedded within larger aggregates but are referenced indirectly through pointers. In the case of a DEFINITIONS module, the sequence of declarations implicitly defines an interface type. There is no explicit name for this type, but it is much like a record type with a field for each item in the interface. Instances of interface types, called interface records, can appear only as components of global frames, where they are anonymous. A program can export an interface, in which case a (partially) initialized interface record is created by the compiler. The initializing values represent procedures, signals, etc., declared within the program. (These values are "relocated" and made instance-specific each time the program is instantiated.) A program can also import an interface to gain access to externally defined procedures and the like. In this case, the interface record is left uninitialized by the Mesa 3.0 Compiler Update