Parsing a Float out of a String

[darrenjw]

For getting data into Dex it would be useful to be able to parse a Float out of a String. I guess I'm looking for a function with a signature like

parse_float (s: String) : Maybe Float

or anything vaguely like "read" in Haskell or "fscanf" in C. Obviously the compiler knows how to do this, but I haven't managed to find it surfaced in Dex. Is there anything like this that I'm missing?

[chenzizhao]

@cyntsh figured out FilePath -> List Float which seems similar to what you were looking for. #543 might be relevant too.

[darrenjw]

Thanks, but I think both of these are related to casting floats stored in binary formats into Dex Floats. What I am interested in is turning a String representation of a Float into a float. So, eg. the ASCII String "12.34" will get turned into the Dex Float 12.34.

[apaszke]

Great question! I think this is one of the pieces we're missing at the moment. Nothing prevents us from reimplementing the Read typeclass in Dex, but it's code that has to be written. I might try to put something together today.

In general, we've been talking for a while about writing a CSV library for Dex, and I imagine this would be one of the prerequisites for that.

[apaszke]

Turns out this can be done fairly easily through C FFI. I wrote an implementation for Float in #974. Please let us know if you need it for any other types!

[darrenjw]

Very cool - many thanks!