Re: X3: Alternative operator doesn't reduce?

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On Fri, Jul 10, 2020 at 6:09 PM Aaron Graham <[email protected]> wrote:

>
>
> On Fri, Jul 10, 2020 at 2:43 PM Michael Powell <[email protected]>
> wrote:
>
>>
>>
>> On Fri, Jul 10, 2020 at 5:38 PM Aaron Graham <[email protected]>
>> wrote:
>>
>>> X3 compound attribute rules
>>> <https://www.boost.org/doc/libs/1_73_0/libs/spirit/doc/x3/html/spirit_x=
3/quick_reference/compound_attribute_rules.html>
>>> say this:
>>>
>>> a: A, b: A --> (a | b): A
>>>
>>>
>>> However, when I write this simple bit of code (exposition purposes only=
):
>>>
>>> #include <boost/spirit/home/x3.hpp>
>>> int main() {
>>>     using namespace boost::spirit::x3;
>>>     auto const quoted_string =3D lexeme['"' >> *(char_ - '"') >> '"'];
>>>     auto value =3D std::string{};
>>>     auto assign_string =3D [&](auto& ctx){ value =3D _attr(ctx); };
>>>     auto const any_string =3D (quoted_string | quoted_string)
>>> [assign_string];
>>>     auto val =3D std::string_view{"\"Test\""};
>>>     phrase_parse(val.begin(), val.end(), any_string, space);
>>> }
>>>
>>>
>>> I get this error:
>>>
>>> error: no match for =E2=80=98operator=3D=E2=80=99 (operand types are =
=E2=80=98std::__cxx11::b
>>> asic_string<char>=E2=80=99 and =E2=80=98
>>> boost::variant<boost::detail::variant::over_sequence<boo
>>> st::mpl::l_item<mpl_::long_<2>, std::__cxx11::basic_string<char>,
>>> boost::mpl::l_
>>> item<mpl_::long_<1>, std::__cxx11::basic_string<char>,
>>> boost::mpl::l_end> > > >=E2=80=99
>>> )
>>>    7 |     auto assign_string =3D [&](auto& ctx){ value =3D _attr(ctx);=
 };
>>>      |
>>>
>>> Why is the attribute a variant instead of a string?
>>>
>>
>> AFAIK, this is the way alternatives have always worked since even before
>> X3.
>>
>
> I've written a lot of very complicated qi parsers and I don't remember
> ever running across this problem. It's possible it just never came up, bu=
t
> I doubt it.
>

In the past, I've identified a couple of areas in the docs that stated one
way, but in reality it was something else. Perhaps this is one of them for
you? I cannot say.

But it doesn't matter. The documentation I linked in my previous email says=
:
>
> a: A, b: A --> (a | b): A
>
> and not:
>
> a: A, b: A --> (a | b): variant<A, A>
>
> But the error message from the compiler clearly expresses that that's wha=
t
> I'm getting. I'll dig into the x3 code when I have some time and try to
> figure it out.
>
> Which being said, I'm not sure it makes a whole lot of sense, even in an
>> academic sense, to alternative, (qs | qs), does it?
>>
>
> I knew someone would answer that way, which is why I had the disclaimer
> "exposition purposes only". My real code looks a little different. But th=
e
> attribute type is the same. The point in this example is to present code
> that's alternating between two clearly identical attribute types.
> _______________________________________________
> Spirit-general mailing list
> [email protected]
> https://lists.sourceforge.net/lists/listinfo/spirit-general
>

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<div dir=3D"ltr"><div dir=3D"ltr"><br></div><br><div class=3D"gmail_quote">=
<div dir=3D"ltr" class=3D"gmail_attr">On Fri, Jul 10, 2020 at 6:09 PM Aaron=
 Graham &lt;<a href=3D"mailto:[email protected]">[email protected]<=
/a>&gt; wrote:<br></div><blockquote class=3D"gmail_quote" style=3D"margin:0=
px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><=
div dir=3D"ltr"><div dir=3D"ltr"><br></div><br><div class=3D"gmail_quote"><=
div dir=3D"ltr" class=3D"gmail_attr">On Fri, Jul 10, 2020 at 2:43 PM Michae=
l Powell &lt;<a href=3D"mailto:[email protected]" target=3D"_blank">mwp=
[email protected]</a>&gt; wrote:<br></div><blockquote class=3D"gmail_quote=
" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);=
padding-left:1ex"><div dir=3D"ltr"><div dir=3D"ltr"><br></div><br><div clas=
s=3D"gmail_quote"><div dir=3D"ltr" class=3D"gmail_attr">On Fri, Jul 10, 202=
0 at 5:38 PM Aaron Graham &lt;<a href=3D"mailto:[email protected]" targ=
et=3D"_blank">[email protected]</a>&gt; wrote:<br></div><blockquote cla=
ss=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid =
rgb(204,204,204);padding-left:1ex"><div dir=3D"ltr">X3 <a href=3D"https://w=
ww.boost.org/doc/libs/1_73_0/libs/spirit/doc/x3/html/spirit_x3/quick_refere=
nce/compound_attribute_rules.html" target=3D"_blank">compound attribute rul=
es</a> say this:<blockquote style=3D"margin:0px 0px 0px 40px;border:none;pa=
dding:0px"><div><span style=3D"color:rgb(0,0,0);font-size:12px">a</span><sp=
an style=3D"font-size:12px;color:rgb(112,112,112)">:</span><span style=3D"c=
olor:rgb(0,0,0);font-size:12px"> </span><span style=3D"color:rgb(0,0,0);fon=
t-size:12px">A</span><span style=3D"font-size:12px;color:rgb(112,112,112)">=
,</span><span style=3D"color:rgb(0,0,0);font-size:12px"> </span><span style=
=3D"color:rgb(0,0,0);font-size:12px">b</span><span style=3D"font-size:12px;=
color:rgb(112,112,112)">:</span><span style=3D"color:rgb(0,0,0);font-size:1=
2px"> </span><span style=3D"color:rgb(0,0,0);font-size:12px">A</span><span =
style=3D"color:rgb(0,0,0);font-size:12px"> </span><span style=3D"font-size:=
12px;color:rgb(112,112,112)">--&gt;</span><span style=3D"color:rgb(0,0,0);f=
ont-size:12px"> </span><span style=3D"font-size:12px;color:rgb(112,112,112)=
">(</span><span style=3D"color:rgb(0,0,0);font-size:12px">a</span><span sty=
le=3D"color:rgb(0,0,0);font-size:12px"> </span><span style=3D"font-size:12p=
x;color:rgb(112,112,112)">|</span><span style=3D"color:rgb(0,0,0);font-size=
:12px"> </span><span style=3D"color:rgb(0,0,0);font-size:12px">b</span><spa=
n style=3D"font-size:12px;color:rgb(112,112,112)">):</span><span style=3D"c=
olor:rgb(0,0,0);font-size:12px"> </span><span style=3D"color:rgb(0,0,0);fon=
t-size:12px">A</span></div></blockquote><div><br></div><div>However, when I=
 write this simple bit of code (exposition purposes only):</div><blockquote=
 style=3D"margin:0px 0px 0px 40px;border:none;padding:0px"><div>#include &l=
t;boost/spirit/home/x3.hpp&gt;</div><div>int main() {</div><div>=C2=A0 =C2=
=A0 using namespace boost::spirit::x3;</div><div>=C2=A0 =C2=A0 auto const q=
uoted_string =3D lexeme[&#39;&quot;&#39; &gt;&gt; *(char_ - &#39;&quot;&#39=
;) &gt;&gt; &#39;&quot;&#39;];</div><div>=C2=A0 =C2=A0 auto value =3D std::=
string{};</div><div>=C2=A0 =C2=A0 auto assign_string =3D [&amp;](auto&amp; =
ctx){ value =3D _attr(ctx); };</div><div>=C2=A0 =C2=A0 auto const any_strin=
g =3D (quoted_string | quoted_string) [assign_string];</div><div>=C2=A0 =C2=
=A0 auto val =3D std::string_view{&quot;\&quot;Test\&quot;&quot;};</div><di=
v>=C2=A0 =C2=A0 phrase_parse(val.begin(), val.end(), any_string, space);</d=
iv><div>}</div></blockquote><div><br></div><div>I get this error:</div><blo=
ckquote style=3D"margin:0px 0px 0px 40px;border:none;padding:0px"><div><spa=
n style=3D"font-family:monospace;font-weight:bold;color:rgb(255,84,84)">err=
or: </span><span style=3D"font-family:monospace;color:rgb(0,0,0)">no match =
for =E2=80=98</span><span style=3D"font-family:monospace;font-weight:bold;c=
olor:rgb(0,0,0)">operator=3D</span><span style=3D"font-family:monospace;col=
or:rgb(0,0,0)">=E2=80=99 (operand types are =E2=80=98</span><span style=3D"=
font-family:monospace;font-weight:bold;color:rgb(0,0,0)">std::__cxx11::b</s=
pan></div><div><span style=3D"font-family:monospace">asic_string&lt;char&gt=
;<span style=3D"color:rgb(0,0,0)">=E2=80=99 and =E2=80=98</span><span style=
=3D"font-weight:bold;color:rgb(0,0,0)">boost::variant&lt;boost::detail::var=
iant::over_sequence&lt;boo</span></span></div><div><span style=3D"font-fami=
ly:monospace">st::mpl::l_item&lt;mpl_::long_&lt;2&gt;, std::__cxx11::basic_=
string&lt;char&gt;, boost::mpl::l_</span></div><div><span style=3D"font-fam=
ily:monospace">item&lt;mpl_::long_&lt;1&gt;, std::__cxx11::basic_string&lt;=
char&gt;, boost::mpl::l_end&gt; &gt; &gt; &gt;<span style=3D"color:rgb(0,0,=
0)">=E2=80=99</span></span></div><div><span style=3D"font-family:monospace"=
>)
</span></div><div><span style=3D"font-family:monospace"> =C2=A0=C2=A0=C2=A0=
7 | =C2=A0=C2=A0=C2=A0=C2=A0auto assign_string =3D [&amp;](auto&amp; ctx){ =
<span style=3D"font-weight:bold;color:rgb(255,84,84)">value =3D _attr(ctx)<=
/span><span style=3D"color:rgb(0,0,0)">; };
</span></span></div><div><span style=3D"font-family:monospace"> =C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0|</span></div><div><br></div></blockquote><div>Why is =
the attribute a variant instead of a string?</div></div></blockquote><div><=
br></div><div>AFAIK, this is the way alternatives have always worked since =
even before X3.</div></div></div></blockquote><div><br></div><div>I&#39;ve =
written a lot of very complicated qi parsers and I don&#39;t remember ever =
running across this problem. It&#39;s possible it just never came up, but I=
 doubt it.</div></div></div></blockquote><div><br></div><div>In the past, I=
&#39;ve identified a couple of areas in the docs that stated one way, but i=
n reality it was something else. Perhaps this is one of them for you? I can=
not say.=C2=A0</div><div><br></div><blockquote class=3D"gmail_quote" style=
=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding=
-left:1ex"><div dir=3D"ltr"><div class=3D"gmail_quote"><div>But it doesn&#3=
9;t matter. The documentation I linked in my previous email says:<br></div>=
</div><blockquote style=3D"margin:0px 0px 0px 40px;border:none;padding:0px"=
><div class=3D"gmail_quote"><div><pre style=3D"color:rgb(0,0,0);font-size:1=
2px"><span>a: A</span><span style=3D"color:rgb(112,112,112)">,</span> <span=
>b</span><span style=3D"color:rgb(112,112,112)">:</span> <span>A</span> <sp=
an style=3D"color:rgb(112,112,112)">--&gt;</span> <span style=3D"color:rgb(=
112,112,112)">(</span><span>a</span> <span style=3D"color:rgb(112,112,112)"=
>|</span> <span>b</span><span style=3D"color:rgb(112,112,112)">):</span> <s=
pan>A</span></pre></div></div></blockquote><div class=3D"gmail_quote"><div>=
and not:</div></div><blockquote style=3D"margin:0px 0px 0px 40px;border:non=
e;padding:0px"><div class=3D"gmail_quote"><div><pre style=3D"color:rgb(0,0,=
0);font-size:12px"><span>a: A</span><span style=3D"color:rgb(112,112,112)">=
,</span> <span>b</span><span style=3D"color:rgb(112,112,112)">:</span> A <s=
pan style=3D"color:rgb(112,112,112)">--&gt;</span> <span style=3D"color:rgb=
(112,112,112)">(</span><span>a</span> <span style=3D"color:rgb(112,112,112)=
">|</span> <span>b</span><span style=3D"color:rgb(112,112,112)">):</span> <=
span>variant</span><span style=3D"color:rgb(112,112,112)">&lt;</span><span>=
A</span><span style=3D"color:rgb(112,112,112)">,</span> A<span style=3D"col=
or:rgb(112,112,112)">&gt;</span></pre></div></div></blockquote><div class=
=3D"gmail_quote"><div>But the error message from the compiler clearly expre=
sses that that&#39;s what I&#39;m getting. I&#39;ll dig into the x3 code wh=
en I have some time and try to figure it out.</div><div><br></div><blockquo=
te class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px =
solid rgb(204,204,204);padding-left:1ex"><div dir=3D"ltr"><div class=3D"gma=
il_quote"><div>Which being said, I&#39;m not sure it makes a whole lot of s=
ense, even in an academic sense, to alternative, (qs | qs), does it?=C2=A0<=
br></div></div></div></blockquote><div><br></div><div>I knew someone would =
answer that way, which is why I had the disclaimer &quot;exposition purpose=
s only&quot;. My real code looks a little different. But the attribute type=
 is the same. The point in this example is to present code that&#39;s alter=
nating between two clearly identical attribute types.</div></div></div>
_______________________________________________<br>
Spirit-general mailing list<br>
<a href=3D"mailto:[email protected]" target=3D"_blank">S=
[email protected]</a><br>
<a href=3D"https://lists.sourceforge.net/lists/listinfo/spirit-general" rel=
=3D"noreferrer" target=3D"_blank">https://lists.sourceforge.net/lists/listi=
nfo/spirit-general</a><br>
</blockquote></div></div>

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