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help with generating Quotations
f#

Hi folks,

I want to write a function that take as an input a ConstructorInfo and return a Quotations.Expr that represents
the creation of this type and the get of the first property.

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let CreateExpr (ci:ConstructorInfo) =
    let myVar = new Var("myVar", ci.ReflectedType)
    Expr.Let(myVar, Expr.Value(null, ci.ReflectedType),
        Expr.PropGet(Expr.AddressOf(Expr.Var(myVar)), ci.ReflectedType.GetProperties().[0]))

[<Struct>]  
type StructTest =
    val mutable public width : single;
    val mutable public height : single;
    new (w, h) = {width = w; height = h}
    new (w) = {width = w; height = w}

let Test () =
    let x = StructTest(1.0f)
    let ci = (x.GetType()).GetConstructors().[1]
    printf "%A" (CreateExpr ci)

do Test ()

It compiles but unfortunately when i run the code i have :

Exception non gérée : Microsoft.FSharp.Core.FailureException: can't take the address of this quotation
à Microsoft.FSharp.Quotations.Patterns.typeOf[ A](A e)
à Microsoft.FSharp.Quotations.Patterns.checkObj(MemberInfo membInfo, Expr obj)
à Microsoft.FSharp.Quotations.Patterns.mkInstancePropGet(Expr obj, PropertyInfo pinfo, List`1 args)

Did i something wrong?

Any help much appreciated!

Stringer

.

Is this what you want?

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let CreateExpr (ci:ConstructorInfo) =
      let myVar = new Var("myVar", ci.ReflectedType)
      let construct = Expr.NewObject(ci, [ Expr.Value(1.0f) ])
      Expr.Let(myVar, Expr.Value(construct, ci.ReflectedType),
            Expr.PropGet(Expr.Var(myVar), ci.ReflectedType.GetProperties().[0]))
By on 2/16/2009 6:17 AM ()

Alright, i think i could live with that for now. But i'm still interested to grok the AddressOf operation and the purpose of the copyOfStruct@58 in my second code sample. Thanks!

By on 2/16/2009 2:20 PM ()

Yes exactly! albeit i'd like to have "construct" buildt with the default constructor instead. I'll try your code sample tonight and see if it works.
Thanks a lot.

Stringer

By on 2/16/2009 6:32 AM ()

Basically the expression i want to generate should be something like expr:

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let Test2 () =
    let expr = <@@let x = new StructTest() in x.width@@>
    printf "%A" expr
do Test2 ()

Exectuting the code results in:

Let (x, Value (<null>),
Let (copyOfStruct@58, x,
PropGet (Some (AddressOf (copyOfStruct@58)), Single width, [])))

As I understand a defensive copy of the immutable value x is made with the introduction of this new Let expression. Plus, copyOfStruct@58 seems to be a mutable variable.

I've tried to mimic it using an intermediate Expr.Let and Expr.VarSet but again with no success (i get an

Microsoft.FSharp.Core.FailureException: unreachable):

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Expr.Let(Var("myVar", ci.ReflectedType), Expr.Value(null, ci.ReflectedType),
    Expr.Let(Var("tmp", ci.ReflectedType, true), Expr.VarSet(Var("tmp", ci.ReflectedType, true), Expr.Var(Var("myVar", 

ci.ReflectedType))),
        Expr.AddressOf(Expr.Var(Var("tmp", ci.ReflectedType)))))

I read chapter 6.4.16.1 of the spec but it didn't help me that much.

Thanks.

Stringer

By on 2/16/2009 5:03 AM ()

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