toexpr_fold.fs

let toExpr (par:ParameterExpression) (clause: Clause) =
    let constExpr (x:'a) =
        Expression.Constant(x, typeof<'a>) |> asExpr
    let callExpr (i:Expression) (m:String) (p:Expression) =
        Expression.Call(i, m, Array.empty, p)        
    let arrExpr (xs:'a array) =
        Expression.NewArrayInit(typeof<'a>, Array.map (constExpr >> asExpr) xs) |> asExpr
    let inExpr (vEx:Expression) (arrEx:Expression) =
        Expression.Call(typeof<Enumerable>, "Contains", [|vEx.Type|], arrEx, vEx) |> asExpr
            
    let simpleF props condition value =
        let lEx = toProperty par props
        let rEx = match value with
                    | Number n      -> constExpr n
                    | Str s         -> constExpr s
                    | Numbers ns    -> arrExpr ns
                    | Strs ss       -> arrExpr ss
        let equality (f:(Expression * Expression) -> BinaryExpression) =
            f (lEx, rEx) |> asExpr
        let call name =
            callExpr lEx name rEx |> asExpr
        match condition with
        | Eq                -> equality Expression.Equal
        | Neq               -> equality Expression.NotEqual
        | Greater           -> equality Expression.GreaterThan
        | Less              -> equality Expression.LessThan
        | GreaterOrEqual    -> equality Expression.GreaterThanOrEqual
        | LessOrEqual       -> equality Expression.LessThanOrEqual
        
        | Contains          -> call "Contains"
        | StartsWith        -> call "StartsWith"
        | EndsWith          -> call "EndsWith"        
        | In                -> inExpr lEx rEx

    let complexF left logOp right =
        let logical (f: Expression * Expression -> BinaryExpression) =
            f (left, right) |> asExpr
        match logOp with
        | Or        -> logical Expression.Or
        | And       -> logical Expression.And

    Clause.Fold simpleF complexF clause