interesting discussion about "scope", note i'm not saying i want Scheme+ act as Python, i'm still thinking the best solution... to be sure about terminology i find this good article about scoping: https://medium.com/altcampus/scope-local-global-and-lexical-e164f53450b3 Damien
On Wed, Sep 22, 2021 at 11:52 PM William ML Leslie < william.leslie....@gmail.com> wrote: > On Thu, 23 Sep 2021, 4:51 am Taylan Kammer, <taylan.kam...@gmail.com> > wrote: > >> On 22.09.2021 11:53, Damien Mattei wrote: >> > i already do it this way for internal defines ,using a recursive macro >> that build a list of variable using an accumulator. It can works but macro >> expansion seems slow, it was not immediate at compilation on a little >> example (oh nothing more that 2 seconds) but i'm not sure it is easily >> maintainable, it is at the limit what macro can do i think ,for speed >> reasons. In fact i can not really understand in Guile as it is based on C >> and compiled when macro expansion happens,what is the time cost... so for >> all those ,perhaps not objective reason ,i prefer to avoid. >> >> I don't think there's any other way to achieve what you want, especially >> using portable Scheme code. The lexical scoping semantics of Scheme are >> a very fundamental part of the language, and cannot be worked around in >> portable Scheme code without using a macro that rewrites whole bodies of >> lambda expressions. >> >> Even using implementation-specific hacks, you won't get very far. Any >> compiled Scheme implementation, and even most interpreted ones, won't >> allow you to modify an outer scope's set of variable definitions from >> within an inner scope. >> >> So if you really want to have Python's scoping semantics in Scheme, you >> will probably have to write a complex 'def' macro that walks through the >> body and "hoists" variable definitions to the outermost scope. >> > > Python is lexically scoped, and the assignment here is supposed to be > local. > > >> If you're targeting R6RS implementations, you can use syntax-case to >> write such a macro, but it won't be easy. >> >> If you're targeting R5RS or R7RS-small implementations, you will have to >> rely on syntax-rules, which will probably be extremely difficult for this >> kind of complex macro. >> >> Personally I don't even know how I would approach the problem using the >> more capable syntax-case, let alone pure syntax-rules. >> >> -- >> Taylan >> >
