Sunday, December 03, 2006

importing other sourcefiles

I think I have finally found a way to have multiple sourcefiles working together. I have based it mostly on the packages system from Java, but I don't call it packages anymore. I have decided to keep the 'namespace' keyword for this purpose. In Java each file that is not in the default package is in some specified package, in Hyper each file is in some namespace. This means that namespaces are no longer declared in blocks like classes are, but they are declared in one line on top of the sourcefile. It will also be possible to have a sourcefile that is not in a namespace; this will be useful for one-file test programs. More about that later. Each sourcefile is in a directory structure that corresponds to the namespace of that file (such as for packages in Java). So a file in namespace "Foo.Bar.Baz" could be named "Foo/Bar/Baz/filename.hyp". A file can import other files by specifying the namespace and name of that file, without the extension. So this will be something like:

namespace Abc.Defg.Stuv.Xy
import Foo.Bar.Baz.filename

There are public and private imports, and an import is private by default. If file 1 is publicly imported in file 2, then any file that imports file 2 will have file 1 imported with it. This is not the case if file 1 is privately imported in file 2. For private imports the compiler will have to check that there are no things from the private import exposed to the outside.

Imports are allowed to be circular; this means that file 1 can import file 2 while file 2 also imports file 1. Such things are of course to be used as little as possible. Disallowing circularity is not feasible because these things are not always avoidable, and the language currently does not allow for forward declarations as C++ does.

A sourcefile that is not in a namespace will not be able to import things from other sourcefiles but only from the standard libraries (system.****). And it cannot be imported by any other sourcefiles. This is to minimize its usage. Files not in a namespace are not in some 'default' namespace as Java does it, but aren't in any namespace at all. So there would be no relation to the directory such a file resides in.

The standard library will use the 'system' keyword as the root namespace. Standard input/output will be available with "import system.stdio". (I think I will use the convention of using a lowercase identifier for the name of a sourcefile) This file contains a static class "StdIO" with a number of procedures for stdout printing. There are "print" procedures for literal printing and "printLn" procedures for printing with an additional newline. This would make the "Hello World"-example look like this:

import system.stdio

class Hello
static procedure main()
system.StdIO.printLn("Hello, World!")

It sure looks better than the current version.

No comments: