[Indigo]<Mesa>Doc>Summary60f.bravo!1

This memo outlines changes made in Mesa since the last alpha update (Mesa 6.0m, September 26, 1980). These changes will shortly be incorporated into the Mesa 6.0 Change Summary to correctly reflect the differences between Mesa 5.0 and Mesa 6.0. This document also includes a list of ARs fixed since 6.0m. Since these versions of the programs are the final release ones, they say 6.0 instead of 6.0f.

In Mesa 6, one can specify a default value for a type or a field of a record. Version 6.0f has some small changes in the interaction of defaults and procedure declarations. The most notable is the ability to specify defaults on result records as well as parameter records. The other difference is that default values in parameter (result) records are not inherited from types with default values. This is best explained by considering some examples, followed by some rules that help explain them.

-- a initialized to TRUE, b initialized to 0, c initialized to NIL
. . .
RETURN[a: FALSE, c: exp]; -- returns [FALSE, 0, exp];.

. . .
RETURN[a:, b:, c: ];-- also illegal. Although c has no default, its need for a
-- non-NULL value, inherited from type Ptr, is retained

There are two uses for default return values: to initialize values of local variables, and as defaults in constructors for result records. The first use is probably the most valuable.

If the type of a field in the result record has a default, the default applies for the initialization of the corresponding local variable, but does not apply in a constructor for the result record. This protects you from assigning a value to a return variable and then forgetting to mention it in a RETURN statement, causing the default for its type to be returned.

If the type of a field has a default, and it is not of the form "← exp | NULL," then the field can be thought of as having a default of the form "←". That is, some non-NULL value must be given in all constructors for that field.

In Mesa 6, you cannot use the values of the parameters in defaults for return values; you must use constants or expressions involving variables global to the procedure. This restriction will probably be lifted in future releases.

The symbol compressor is available again. It can be found on the >Binder subdirectory of the release directory as SymbolCompressor.bcd. To use it, load it ahead of the Biinder and specify the /x switch. Thus

will create Foo.bcd and Foo.symbols (compressed). Compressed symbols are more compressed than they were in Mesa 5. They contain just the (public and private) procedures and signals declared at the top level of the module.

The switches to copy code (/c), to copy symbols (/s), and to compress symbols (/x) may now be given as global switches, and hence apply to all source files thereafter.

In earlier versions, copying symbols was an error if not all of the symbol files were available at bind time. The binder now copies all symbols that it can find, leaves the symbol table references for the other modules in the original (unavailable) files, and issues a warning.

The cursor now changes as soon as warnings or errors are logged by the binder, in case you aren’t suspecting them and want to stop things and look around.

The Debugger now knows how to index sequences. Thus, if seq is a pointer to a record containing a sequence part, say items, the interpreter commands

When you set an exit break on a procedure, you take the break on any return (they jump to a common instruction to make this easy on the debugger). The debugger has no way of telling you which return was taken if there is more than one. When asked for source, the debugger now shows the first line of the procedure declaration instead of the last return.

Even if a module has compressed symbols, the debugger will first look around for the file modulename.bcd and see if it is the original compiler output for that module (by checking the version stamp). If so, it will use those symbols. Thus, there is no need to Attach Symbols if the proper file is on the disk. It makes sense to compress symbols for large systems and have around the complete symbols for specific modules undergoing detailed debugging.

The debugger does a better job of determining signed/unsigned representation of values given to the interpreter. For example, any octal number is assumed to be unsigned.

Instead of the File Tool, one should use Fetch.bcd, available on the release directory, to have a file transfer facility within XDebug. The necessary Pup machinery is part of Fetch.bcd.

The command for moving the insert point in the editor has been changed to Control-Red (from Shift-Red) partly to benefit the sanity of Laurel 6 modeless editor users. The debugger will now complain if you try to Kill session when you are editing a file (you can, however, Proceed).

The command scanner for the lister now allows optional quotes on string parameters. Anything up to the next comma or right bracket is considered the parameter. Of course you can still type them, and must if the parameter contains a comma or right bracket (I can’t think of any lister commands where this makes sense, though). In addition, there are several new lister commands of general interest.

FileName is a list of BCDs, separated by spaces (such as object.system). The lister produces a file root[FileName].iml (e.g. object.iml) that contains a listing of exported interfaces, together with the name of the program module implementing each interface item. If the given interface is also named in the input file, the output will also include those interface items not implemented by any programs in the collection. In order to run this command, you have to have symbols for all of the exported interfaces as well as all of the items named in the input file.

FileName is a Compiler or Binder or Packager output BCD. The lister produces the file Filename.bl that contains the version stamp of any modules bound in the BCD, and the version stamps for all imported and exported interfaces. This command should replace most uses of the Bcd["FileName"] command and produces output much easier to read.

FileName is a Compiler or Binder or Packager output BCD. The lister produces the file FileName.xl that shows, for each exported interface, which items are not implemented. In order to run this command, you need the symbols for any exported interface that is not completely implemented. The lister will complain about missing ones.

FileName is a Compiler or Binder or Packager output BCD, or an image file. The lister shows, on Mesa.typescript, the version stamps for the file, its creator, and its source.

The debugger will now complain if you try to exit the debugger (compile!, bind!, run!, or go!) while editing a file.