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.

[foonathan]

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

[foonathan]

Relevant resources for float parsing:

• https://github.com/lemire/fast_double_parser
• https://arxiv.org/abs/2101.11408
• https://www.exploringbinary.com/how-strtod-works-and-sometimes-doesnt/

[jokoon]

Are you planning to parse those as valid?
.3
0.
43.

I think I managed to parse those at one point, but it was 2 additional rules, so it was not very efficient.

I don't know what ISO or other standard say about this, but to me it seems that something like .003 should not be standard, but as soon as it's valid code somewhere, people are going to ask for it.

[foonathan]

The interface I'm imagining is similar to the split between dsl::digits and dsl::integer.

I'm envisioning a dsl::number rule that takes token rules. One for matching the integer part, one for matching a fractional part, and one for matching the exponent.

So you can completely define what's considered to be valid.