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f#quotations
Onur Gumus
Onur Gumus

Reputation: 1439

Quotation Transformation in F# to another type

I have the following types:

type Foo = { Name : string}
type Bar = {Name : string}

And I have the following Quoted expression:

<@ fun (x : Foo) -> x.Name = "1" @>

Basically from this I would like to generate another quoted expression as:

<@ fun (x : Bar) -> x.Name = "1" @>

How can I do this?

Upvotes: 0

Views: 79

Answers (1)

Onur Gumus
Onur Gumus

Reputation: 1439

OK I got the following solution :

let subst expression newType =
    let newVar name = Var.Global(name,newType)

    let rec substituteExpr expression  =
        match expression with
        | Call(Some (ShapeVar var),mi,other) ->
          Expr.Call(Expr.Var(newVar var.Name), newType.GetMethod(mi.Name),other)
        | PropertyGet (Some (ShapeVar var)  ,pi, _) ->
            Expr.PropertyGet(Expr.Var( newVar var.Name), newType.GetProperty(pi.Name),[])
        | ShapeVar var -> Expr.Var <| newVar var.Name
        | ShapeLambda (var, expr) ->
            Expr.Lambda (newVar var.Name, substituteExpr expr)
        | ShapeCombination(shapeComboObject, exprList) ->
            RebuildShapeCombination(shapeComboObject, List.map substituteExpr exprList)
    substituteExpr expression

then I can do

let f = <@ fun (x : Foo) -> x.Name = "1" @>
let transformed =  subst f typeof<Bar>
let typedExpression: Expr<Bar -> bool> = downcast <@ %%transformed @>

Upvotes: 1

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