(* Copyright (c) 2008, Adam Chlipala
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * - Redistributions of source code must retain the above copyright notice,
 *   this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright notice,
 *   this list of conditions and the following disclaimer in the documentation
 *   and/or other materials provided with the distribution.
 * - The names of contributors may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 
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 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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 *)

(* Simplify a Core program algebraically *)

structure Reduce :> REDUCE = struct

open Core

structure E = CoreEnv
structure U = CoreUtil

val liftConInCon = E.liftConInCon

val subConInCon =
    U.Con.mapB {kind = fn k => k,
                con = fn (xn, rep) => fn c =>
                                  case c of
                                      CRel xn' =>
                                      if xn = xn' then
                                          #1 rep
                                      else
                                          c
                                    | _ => c,
                bind = fn ((xn, rep), U.Con.Rel _) => (xn+1, liftConInCon 0 rep)
                        | (ctx, _) => ctx}

fun bindC (env, b) =
    case b of
        U.Con.Rel (x, k) => E.pushCRel env x k
      | U.Con.Named (x, n, k, co) => E.pushCNamed env x n k co

fun bind (env, b) =
    case b of
        U.Decl.RelC (x, k) => E.pushCRel env x k
      | U.Decl.NamedC (x, n, k, co) => E.pushCNamed env x n k co
      | U.Decl.RelE (x, t) => E.pushERel env x t
      | U.Decl.NamedE (x, n, t, eo) => E.pushENamed env x n t eo

fun kind k = k

fun con env c =
    case c of
        CApp ((CAbs (_, _, c1), loc), c2) =>
        #1 (reduceCon env (subConInCon (0, c2) c1))
      | CNamed n =>
        (case E.lookupCNamed env n of
             (_, _, SOME c') => #1 c'
           | _ => c)
      | CConcat ((CRecord (k, xcs1), loc), (CRecord (_, xcs2), _)) => CRecord (k, xcs1 @ xcs2)
      | _ => c

and reduceCon env = U.Con.mapB {kind = kind, con = con, bind = bindC} env

fun exp env e = e

fun decl env d = d

val reduce = U.File.mapB {kind = kind, con = con, exp = exp, decl = decl, bind = bind} CoreEnv.basis

end