compiler: remove references to predicated types for now

compiler/tyscheme.sml

 structure TyScheme: sig
 
-  type tyScheme = {sigmas: string list, rhos: (string * Ty.ty) list, tau: Ty.ty}
+  type tyScheme = {sigmas: string list, tau: Ty.ty}
 
   val generalize: Ty.ty -> tyScheme
 
@@ -10,7 +10,7 @@ structure TyScheme: sig
 
 end = struct
 
-  type tyScheme = {sigmas: string list, rhos: (string * Ty.ty) list, tau: Ty.ty}
+  type tyScheme = {sigmas: string list, tau: Ty.ty}
 
   local open Ty in
   fun freeVars' (Unit | Bool | Int) = []
@@ -28,16 +28,15 @@ end = struct
   val freeVars = dedup o freeVars'
 
   fun generalize ty =
-    {sigmas = freeVars ty, rhos = [], tau = ty}
+    {sigmas = freeVars ty, tau = ty}
 
-  fun instantiate {sigmas = sigmas, rhos = _, tau = ty} =
+  fun instantiate {sigmas = sigmas, tau = ty} =
     foldl (fn (a, inner) => Unify.subst (Ty.freshTyVar ()) a inner) ty sigmas
 
   local open Utils in
-  fun untyScheme {sigmas = sigmas, rhos = rhos, tau = ty} =
+  fun untyScheme {sigmas = sigmas, tau = ty} =
     cat (
       (map (fn a => cat ["\\/", a, "."]) sigmas) @
-      (map (fn (x, t) => (paren o spc) [x, "::", Ty.unty t]) rhos) @
       [Ty.unty ty]
     )
   end