reference implementation of a vector swizzle library

This also provides the initial steps towards support for type class "filtered" type inference
fixes an "ordinal type expected" ICE, related to the use of static params

compiler/semcall.nim

@@ -228,12 +228,25 @@ proc indexTypesMatch(c: PContext, f, a: PType, arg: PNode): PNode =
   if m.genericConverter and result != nil:
     instGenericConvertersArg(c, result, m)
 
-proc convertTo*(c: PContext, f: PType, n: PNode): PNode = 
+proc inferWithMetatype(c: PContext, formal: PType,
+                       arg: PNode, coerceDistincts = false): PNode =
   var m: TCandidate
-  initCandidate(c, m, f)
-  result = paramTypesMatch(m, f, n.typ, n, nil)
+  initCandidate(c, m, formal)
+  m.coerceDistincts = coerceDistincts
+  result = paramTypesMatch(m, formal, arg.typ, arg, nil)
   if m.genericConverter and result != nil:
     instGenericConvertersArg(c, result, m)
+  if result != nil:
+    # This almost exactly replicates the steps taken by the compiler during
+    # param matching. It performs an embarassing ammount of back-and-forth
+    # type jugling, but it's the price to pay for consistency and correctness
+    result.typ = generateTypeInstance(c, m.bindings, arg.info,
+                                      formal.skipTypes({tyCompositeTypeClass}))
+  else:
+    typeMismatch(arg, formal, arg.typ)
+    # error correction:
+    result = copyTree(arg)
+    result.typ = formal
 
 proc semResolvedCall(c: PContext, n: PNode, x: TCandidate): PNode =
   assert x.state == csMatch