Fixed type inference issues with ITuple active patterns (#95)

src/QsCompiler/DataStructures/SyntaxExtensions.fs

@@ -298,27 +298,30 @@ type QsTuple<'I> with
 
 // active pattern for tuple matching
 
-let private TupleItems<'I> (arg : ITuple) = arg |> function  // not the nicest solution, but unfortunatly type extensions cannot be used to satisfy member constraints...
-    | :? QsExpression               as arg -> arg.TupleItems |> Option.map (List.map box)
-    | :? TypedExpression            as arg -> arg.TupleItems |> Option.map (List.map box)
-    | :? QsType                     as arg -> arg.TupleItems |> Option.map (List.map box)
-    | :? ResolvedType               as arg -> arg.TupleItems |> Option.map (List.map box)
-    | :? QsInitializer              as arg -> arg.TupleItems |> Option.map (List.map box)
-    | :? ResolvedInitializer        as arg -> arg.TupleItems |> Option.map (List.map box)
+ // not the nicest solution, but unfortunatly type extensions cannot be used to satisfy member constraints...
+ // the box >> unbox below is used to cast the value to the inferred type of 'T
+let private TupleItems<'T when 'T :> ITuple> (arg: 'T): 'T list option =
+    let cast a = box >> unbox |> List.map |> Option.map <| a
+    match box arg with
+    | :? QsExpression               as arg -> cast arg.TupleItems
+    | :? TypedExpression            as arg -> cast arg.TupleItems
+    | :? QsType                     as arg -> cast arg.TupleItems
+    | :? ResolvedType               as arg -> cast arg.TupleItems
+    | :? QsInitializer              as arg -> cast arg.TupleItems
+    | :? ResolvedInitializer        as arg -> cast arg.TupleItems
     // TODO: can be made an ITuple again once empty symbol tuples are no longer valid for functor specialiations...
-    //| :? QsSymbol                   as arg -> arg.TupleItems |> Option.map (List.map box) 
-    | :? SymbolTuple                as arg -> arg.TupleItems |> Option.map (List.map box)
+    //| :? QsSymbol                   as arg -> arg.TupleItems |> Option.map (List.map box)
+    | :? SymbolTuple                as arg -> cast arg.TupleItems
     | _ -> InvalidOperationException("no extension provided for tuple matching of the given ITuple object") |> raise
 
 let (| Item | _ |) arg =         
     match TupleItems arg with
-    | Some [item] -> Some (item |> unbox)
+    | Some [item] -> Some item
     | _ -> None
 
 let (| Tuple | _ |) arg =         
-    match TupleItems arg with 
-    | Some [] | Some [_] -> None
-    | Some items when items.Length > 1 -> Some (items |> List.map unbox)
+    match TupleItems arg with
+    | Some items when items.Length > 1 -> Some items
     | _ -> None
 
 let (| Missing | _ |) arg =