How to pass LinQ Expressions from F# to C# code

Question

ReactiveUI has methods with signitures like

public static ReactiveUI.ObservableAsPropertyHelper<TRet> 
  ObservableToProperty<TObj, TRet>(
    this TObj This, 
    System.IObservable<TRet> observable, 
    System.Linq.Expressions.Expression<System.Func<TObj, TRet>> property, 
    TRet initialValue = null, 
    System.Reactive.Concurrency.IScheduler scheduler = null
  )

In F# How would I construct an object like

System.Linq.Expressions.Expression<System.Func<TObj, TRet>> property,

In C# I would do something like

this.ObservableAsPropertyHelper(
    observable,
    me => me.MyProperty
)

EDIT

I've tried

m.ObservableToProperty(this, value, fun me -> me.Property )

and

m.ObservableToProperty(this, 
            value, 
            new Linq.Expression.Expression(fun me -> me.Property )

but neither work

Ramon Snir · Accepted Answer · 2012-12-14T16:06:25.907

5

I'm not sure if the new F# 3 query expressions help you, but the old PowerPack (which still works great!) has an extension method Expr.ToLinqExpression() : Expression, to compile F# quotation expressions (i.e. <@ fun me -> me.MyProperty @>) into LINQ expressions.

Edit: As Daniel had pointed out, QuotationToLambdaExpression does the works, for F# 3.

edited Dec 14 '12 at 16:06

answered Dec 14 '12 at 08:26

Ramon Snir

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Tried that but I got a result of type "LinqExpression" instead of "LinqExpression>" – bradgonesurfing Dec 14 '12 at 09:09
@bradgonesurfing http://msdn.microsoft.com/en-us/library/bb335710.aspx, specifically `Use the Lambda(Expression, IEnumerable) or Lambda(Expression, ParameterExpression[]) method to create an Expression object.` . – Ramon Snir Dec 14 '12 at 10:04
8

It looks like [`QuotationToLambdaExpression`](http://msdn.microsoft.com/en-us/library/hh324072.aspx) is the way to do it in F# 3.0. – Daniel Dec 14 '12 at 15:16

How to pass LinQ Expressions from F# to C# code

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