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Re: macro-replacement with quotes


From: Marcin Borkowski
Subject: Re: macro-replacement with quotes
Date: Mon, 25 Jan 2016 12:10:38 +0100
User-agent: mu4e 0.9.13; emacs 25.1.50.1

On 2016-01-25, at 11:17, Phillip Lord <address@hidden> wrote:

> Marcin Borkowski <address@hidden> writes:
>
>> On 2016-01-24, at 22:56, Phillip Lord <address@hidden> wrote:
>>
>>> Is it possible to build a list within a macro which contains backquote,
>>> quote or comma symbols in it?
>>>
>>> Specifically, I was thinking of building a macro which expands to a
>>> pcase form, but I need the ` symbol in the expansion.
>>
>> I'm not sure whether this would help (I know next to nothing about
>> pcase), but would \` and \, suffice for you?
>>
>> If I do M-: (read) and type `(a ,b), I get (\` (a (\, b))), which seems
>> to be equivalent to `(a ,b) in terms of `eval'.  Dunno about pcase,
>> though.
>>
>>> Phil
>>
>> Best,
>
>
> Hmm, yes, you are right. I didn't realise that (\` x) was equivalent to
> `x, but this works...
>
> (pcase 10
>   ((\` (\, a)) a))
>
> And this...
>
> (defun quote-and-comma-arg (def)
>   (list '\` (list (list '\, (car def)))))
>
> (defmacro p-test (def)
>   `(pcase 10
>      (,(quote-and-comma-arg def)
>       ,(car def))))
>
> (p-test (a))
>
> expands to
>
> (pcase 10
>   (`(,a)
>    a))
>
> which returns "10".
>
> The joy of lisp!

Glad that it helped.

It occurred to me now that another way might be to use something like
``(a b), which apparently yields a similar result, but less of a pain to
type.

Best,

-- 
Marcin Borkowski
http://octd.wmi.amu.edu.pl/en/Marcin_Borkowski
Faculty of Mathematics and Computer Science
Adam Mickiewicz University



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