I could solve the problem for this particular case (in fact we discussed options on the list), but really, this kind of ‘enigmatic’ error creeps up more often with Boost Spirit and it would be nice to get a handle on the general class of problems. Your first resource should be the excellent spirit documentation, … Read more
qi::hold is one way about it, as correctly mentioned by @Andrzej I think I have a few observations that might help, as well as a better solution. The point is that Spirit will not require ‘temp’ storage for attributes by design. In fact, it can’t really assume the attribute be copyable in the first place. … Read more
This a really good question (and also a can of worms) because it gets at the interface of qi and phoenix. I haven’t seen an example either, so I’ll extend the article a little in this direction. As you say, functions for semantic actions can take up to three parameters Matched attribute – covered in … Read more
UPDATE Since Spirit X3 is available for testing, I’ve updated the benchmarks. Meanwhile I’ve used Nonius to get statistically sound benchmarks. All charts below are available interactive online Benchmark CMake project + testdata used is on github: https://github.com/sehe/bench_float_parsing Summary: Spirit parsers are fastest. If you can use C++14 consider the experimental version Spirit X3: The … Read more
Here is an implementation based on Boost Spirit. Because Boost Spirit generates recursive descent parsers based on expression templates, honouring the ‘idiosyncratic’ (sic) precedence rules (as mentioned by others) is quite tedious. Therefore the grammar lacks a certain elegance. Abstract Data Type I defined a tree data structure using Boost Variant’s recursive variant support, note … Read more
In general the following directives are helpful for inhibiting/switching skippers mid-grammar: qi::lexeme [ p ]which inhibits a skipper, e.g. if you want to be sure you parse an identifier without internal skips) – see also no_skip for comparison qi::raw [ p ]which parses like always, including skips, but returns the raw iterator range of the … Read more
I’m sure Hartmut will answer in a second. Till then, this is my take: No that is not an official point. Semantic actions have some drawbacks The simplest disadvantage of semantic actions is the stylistic notion of separation of concerns. You want to express syntax in one place, and semantics in another. This helps maintainability … Read more