dsl for real numbers

[facontidavide]

I am new to the library so I apologize if I am missing something.

Exploring the examples I can't find anything similar to dsl::integer for real numbers. O course I understand that parsing real numbers is complicated having a lot of different representations, but I would need something simple such as 5.67 to start with.

My application is an AST similar to the calculator example.

[foonathan]

I plan on adding that in the future.

What I'm doing right now as a workaround is to manually parse digits + period + digits, capture that and call std::stod/std::from_chars on the lexeme.

[facontidavide]

Would you mind adding a code snippet ? (I am trying to do the same)

[foonathan]

https://godbolt.org/z/1WExWsod9

If you want to use a different decimal separator, you need to capture each dsl::digits part individually and then manually build a string in the format expected by std::stod.

[facontidavide]

Thanks. You saved me a ton of time :smile: .

I am still learning, and I would have needed a lot of time to figure this out.

[foonathan]

I'm reopening this as I do want to add it properly.

[facontidavide]

I am using type erased numbers (for the sake of simplicity, let's assume it is std::variant<int,double>).

The matching doesn't seem to work as expected if I do this: https://godbolt.org/z/jWG4zoKTP

test string would be:

• -7 -> expects int: -7
• 3.14 -> expects double: 3.14
• 1e2 -> expects double: 100
• 0x7 -> expects int: 7
• 0x7e8 -> expects error

My point is that if you are implementing dsl::real, it would be interesting to use it alongside dsl::integer.

[facontidavide]

I am realizing that what I should probably do is similar to ast::json_number in the json.cpp example

[foonathan]

The matching doesn't seem to work as expected if I do this: https://godbolt.org/z/jWG4zoKTP

Choice is ordered and takes the first branch that matches. When it sees 5.3 dsl::integer matches so that is parsed; it then leaves .3 unconsumed. I recommend attempting to match the real number first and ensuring that it does not match integers only: https://godbolt.org/z/dn83sxqdG

Please ask more questions in the discussions in the future.