Hi all, from time to time, the issue of symbol namespaces (or the lack of them) in PicoLisp is brought up again.
Personally, I think that namespaces (that is, different sets of interned symbols in different contexts) may confuse more than they do really help. But with transient symbols we do already have a certain kind of namespaces, implicit by the lexical (source file) context. So I decided to go ahead, and implement "named" symbol namespaces ... if we regard transient symbols as residing in the own anonymous namespaces. This feature is available only in the 64-bit version. It could perhaps be implemented also in Ersatz and MiniPicoLisp, but unfortunately not in the 32-bit version, because of its different symbol table mechanism. The underlying concepts are very simple. Only a single new function was added, 'symbols', and a new global 'pico' holding the initial (default) symbol namespace. If 'symbols' is never called, everything should work as before. Calling it without arguments : (symbols) -> pico returns the current namespace. If you call it with the name of a new namespace and the name of an existing namespace : (symbols 'myNames 'pico) -> pico the following happens: The symbol 'myNames' (existing in the current namespace) receives a _copy_ of the namespace 'pico', and is made the new current one. Check: : (symbols) -> myNames After a namespace is created that way, it is independent from other namespaces. New symbols will be added here, and deleting symbols (with 'zap') will not influence other namespaces. Thus, a symbol will not be garbage collected as long as it is referred to from at least one namespace. Symbols from other namespaces, when visible in data structures, will appear as transient symbols. If you call 'symbols' with a single argument, it should be an existing namespace, and this will be set to be the new current one. : (symbols 'pico) -> myNames The previously current namespace is returned. Check: : (symbols) -> pico Fiddling around with symbols named "Foo": : (zero Foo) -> 0 : (symbols 'myNames) -> pico : (one Foo) -> 1 : Foo -> 1 : (symbols 'pico) -> myNames : Foo -> 0 To access a symbol in another namespace, we can use a tilde character separating a namespace from a symbol. The tile was chosen because it possibly does not conflict with the rest of the PicoLisp syntax. : myNames~Foo -> 1 : (setq myNames~Bar 'myNames~Foo) -> "Foo" : Bar -> NIL : (symbols 'myNames) -> pico : Bar -> Foo This syntax can also be chained, e.g. myNames~yourNames~foo I have released a new testing version as a draft. Documentation and unit tests are still missing, though. Any opinions? Cheers, - Alex -- UNSUBSCRIBE: mailto:picolisp@software-lab.de?subject=Unsubscribe
