Converting C# Expression Parsing to F#

Question

As a newbie to F#, I routinely try to convert bits of C# over as a learning exercise. In this case, I am trying to convert the following C# expression parsing code. It's simple, the idea is to pass a lambda into this function to get the string representation of a property name, rather than using standard reflection techniques. I have omitted the other GetMemberName function as I think I can figure it out once I get some guidance on what approach to take.

public static string GetMemberName<T>(Expression<Func<T, object>> expression)
{
    if (expression == null)
    {
        throw new ArgumentException("The expression cannot be null.");
    }
    return GetMemberName(expression.Body);
}

I know that F# has quotations. I also know I could use Linq Expressions in F#. I would like to try it the F# way first using quotations, but I am stumbling. Could someone give me a kickstart?

Daniel · Accepted Answer · 2014-11-11 15:41:09Z

3

I'm not sure if an exact translation of this is possible using quotations because quotations have a different shape than C# expressions. However, here's something along the same lines:

open Microsoft.FSharp.Quotations.Patterns

let GetMemberName = function
    | Call (_,methodInfo,_) -> methodInfo.Name
    | PropertyGet (_,propertyInfo,_) -> propertyInfo.Name
    | _ -> failwith "Not a member expression"

GetMemberName <@ [].IsEmpty @>
// val it : string = "IsEmpty"

edited Nov 11, 2014 at 15:41

answered Nov 11, 2014 at 15:12

Daniel

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4 Comments

bp123 Over a year ago

OK, but isn't this just regular reflection rather than expression parsing?

Daniel Over a year ago

I'm not sure I follow the distinction you're making. I added example usage to the answer. Hopefully that will help clarify.

svick Over a year ago

@bp123 Both LINQ Expressions and F# quotations work with .Net reflection types. There is no text parsing (is that what you meant?) in either case.

bp123 Over a year ago

Gotcha - this is due to my ignorance, apologies. I thought that parsing an expression in C# for the purposes of a function like the one I posted was different than reflection.

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