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On 05/22/2013 08:12 AM, John Cowan wrote:
Alex Shinn scripsit:SRFI-108 is pretty huge and scares me somewhat.
It's basically Scribble with a slightly different syntax, meant to share syntax with SRFI-109 quasi-strings. The major non-syntax issue is that a tag &foo maps to $construct$:foo rather than plain foo, to allow different bindings for &foo and foo.
I think the core is pretty simple. For objects you want to initialize
from a literal string, you write:
&name{string}
which is lexed as
($construct$:name "string")
If you want expressions instead, you write:
&name[expr expr expr]
Actually, at your request, the specification
requires a following {}. I.e.
&name[expr expr expr]{}
This is because of concerns about ambiguity with &foo
as a name, for example for an exception-type.
Kawa does not require the '{}'. Personally, I don't
think the ambiguity is a real problem: &foo immediately
followed by '[' with no intervening spaces can be read
pretty unambiguously a SRFI-108 form.
which is lexed as
($construct$:name $<< expr expr expr $>>$)
where $<<$ and $>>$ are variables defined by the implementation as
distinct objects, typically empty strings.
Actually,
&name[expr expr expr]{}
is lexed as:
($construct$:name expr expr expr $>>$)
i.e. without the initial $<<$. This is to allow disambiguating
&name{&[expr expr expr]}
which is lexed as:
($construct$:name $<<$ expr expr expr $>>$)
--
--Per Bothner
per@xxxxxxxxxxx http://per.bothner.com/