IntRank

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(*  Mini, a type inference engine based on constraint solving.            *)

(*  Copyright (C) 2006. François Pottier, Yann Régis-Gianas               *)

(*  and Didier Rémy.                                                      *)

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(* $Id: intRank.ml 421 2006-12-22 09:27:42Z regisgia $ *)

(** This module defines integer ranks.

The constraint solver assigns a nonnegative integer rank to every type variable that is currently in scope, that is, every type variable in dtv(S), where S is the current stack. The rank of a variable bound at the outermost level is 0; the rank of a variable bound at the kth let frame down the stack is k. Type variables that are not currently in scope include the universal quantifiers of type schemes that appear in environment frames, which by convention have rank none, as well as type variables that are bound inside an external constraint (that is, a constraint that has not yet been examined by the solver), whose rank is irrelevant. *)



type t = int

(** compare is the usual total ordering on integers. *)



let compare = (-)

(** none is the special value used to identify the universal quantifiers of a type scheme in an environment frame. Such variables are not part of dtv(S), that is, the type variables currently in scope, which explains why they do not carry a nonnegative integer rank. *)



let none = -1

(** outermost is the rank assigned to variables that are existentially bound at the outermost level. *)



let outermost = 0