[Python-ideas] User-defined literals

Paul Moore p.f.moore at gmail.com
Fri Jun 5 14:09:20 CEST 2015

On 4 June 2015 at 23:31, Nick Coghlan <ncoghlan at gmail.com> wrote:
>> The fundamental difference between this proposal and mine is (I think)
>> that you're assuming an arbitrary Python expression in there (which is
>> parsed), whereas I'm proposing an *unparsed* string.
> No, when you supplied a custom parser, the parser would have access to the
> raw string (as well as the name -> cell mapping for the current scope).
> The "quoted AST parser" would just be the default one.

Ah, I see now what you meant. Apologies, I'd not fully understood what
you were proposing. In which case yes, your proposal is strictly more
powerful than mine.

You still have the same problem as me, that what's inside !xxx(...)
cannot contain a ")" character. (Or maybe can't contain an unmatched
")", or an unescaped ")", depending on what restrictions you feel like
putting on the form of the unparsed expression...) But I think that's
fundamental to any form of syntax embedding, so it's not exactly a


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