Re: new function

[Damien Mattei <damien.mattei@gmail.com>]

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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.ttg@gmail.com> wrote:

> On Thu, 23 Sep 2021, 4:51 am Taylan Kammer, <taylan.kammer@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
>>
>

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