Add subscript operator to Expression to access sub-expressions by name

[jteuber]

Hi there!
It might be just me, but accessing certain sub-expressions of a rule by name seems very handy for me, especially with very complicated rules. So I added this. It seems to work quite well. Especially the std::optional makes parsing expressions with optional expressions much simpler.

[TheLartians]

Hey, thanks for the PR, I definitely see the advantages of the rule based query, and good call with the optional return! Could you also add a test case, so the feature remains stable in the future?

[jteuber]

Sure, there you go! :)

[codecov]

Codecov Report

Merging #60 (e1b5022) into master (dcec3a0) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #60      +/-   ##
==========================================
+ Coverage   97.67%   97.69%   +0.02%     
==========================================
  Files           9        9              
  Lines         646      652       +6     
==========================================
+ Hits          631      637       +6     
  Misses         15       15              

Impacted Files	Coverage Δ
include/peg_parser/interpreter.h	95.71% <100.00%> (+0.40%)	⬆️

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[TheLartians]

Hey, thanks for adding the test case! I do find it to be a hard to follow, as it's doing a lot of things at once. What do you think about simplifying it to a single rule that checks the new [string] operator?

For example, something like

  ParserGenerator<bool> program;
  program["Word"] << "[a-z]+";
  program["Yell"] << "[A-Z]+";
  program["Start"] << "Word | Yell" >> [](auto e){ return bool(e["Yell"]);  }
  REQUIRE(!program.run("hello"));
  REQUIRE(program.run("HELLO"));

should be enough.

[jteuber]

Yes, you're absolutely right. That's a much better test case. I had a hard time coming up with a simple test yesterday so I basically simplified the use case I had for the subscript operator. As soon as I have some time on my PC today I copy over your suggestion. Feb 5, 2021 10:43:43 Lars Melchior <notifications@github.com>:

…

@TheLartians commented on this pull request. ---------------------------------------- In test/source/parser.cpp[#60 (comment)]: > +  ParserGenerator<std::string> program; +  program.setSeparator(program["Whitespace"] << "[\t ]"); + +  program["Word"] << "[a-z]+"; +  program["Yell"] << "[A-Z]+"; +  program["Number"] << "[0-9]+"; +  program["IntSubscript"] << "Word Yell? Number" >> [](auto e) { return e[1].string(); }; +  program["StringSubscriptOptional"] << "Number Yell? Word" >> [](auto e) { +    if (auto expr = e["Yell"]) return expr->string(); +    return std::string(); +  }; +  program["Start"] << "IntSubscript | StringSubscriptOptional"; + +  program.setStart(program["Start"]); + +  REQUIRE(program.run("ab 0") == "0"); +  REQUIRE(program.run("ab CD 1") == "CD"); +  REQUIRE(program.run("2 ef") == ""); +  REQUIRE(program.run("2 GH ij") == "GH"); Hey, thanks for adding the test case! I do find it to be a hard to follow, as it's doing a lot of things at once. What do you think about simplifying it to a single rule that checks the new [string] operator? For example, something like   ParserGenerator<bool> program;   program["Word"] << "[a-z]+";   program["Yell"] << "[A-Z]+";   program["Start"] << "Word | Yell" >> [](auto e){ return bool(e["Yell"]);  }   REQUIRE(!program.run("hello"));   REQUIRE(program.run("HELLO")); — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub[#60 (review)], or unsubscribe[https://github.com/notifications/unsubscribe-auth/ADTEN343AV7EBEC4YRMQ3L3S5O4U3ANCNFSM4XBT36QA]. [data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAADUAAAA1CAYAAADh5qNwAAAAAXNSR0IArs4c6QAAAARzQklUCAgICHwIZIgAAAAiSURBVGiB7cEBDQAAAMKg909tDjegAAAAAAAAAAAAAIB7AywZAAGURgP6AAAAAElFTkSuQmCC###24x24:true###][Tracking image][https://github.com/notifications/beacon/ADTEN37QNKKWFOYXQNH6H5DS5O4U3A5CNFSM4XBT36QKYY3PNVWWK3TUL52HS4DFWFIHK3DMKJSXC5LFON2FEZLWNFSXPKTDN5WW2ZLOORPWSZGOELI4MCQ.gif]

[TheLartians]

Awesome, thanks for the PR and updates!

[TheLartians]

The feature is released in v2.2.0! 🎉