Question

I am writing a conversion function for units of measurements in F#. The information regarding the values is coming from an ASP.NET web application.

The function I am creating is defined like this:

let convert (x:float<_>) (toType : string) =
  // Do conversion here.

The first problem I am running into involves the toType : string definition. Is there any way I can make define it to accept a float<_> type…particularly coming from the web application? (I know it’s part of the CLR based on Andrew Kennedy’s excellent articles, but I don’t see how to generically define it in the function.

Thanks for any help you can provide.

Answer 1

If you just want to be able to read in “2.0 ft” and “5.0 m” then

• you should write code that parses the strings and does some conditional logic (e.g. if “ft” then turn into float<ft> or whatever)

• once you have the data converted into the F# type system you can do things in a typesafe way

This is typical of every app that wants to get strongly-typed data in from the outside world; there is an input component that must parse and validate the input and store it into a strongly-typed data structure, but then the program can use that data henceforth.

(There’s no magical parser/input validator in any library, you just do it for your data types.)