(*  Title:      nominal_permeq.ML
    Author:     Christian Urban
    Author:     Brian Huffman
*)

signature NOMINAL_PERMEQ =
sig
  val eqvt_tac: Proof.context -> thm list -> string list -> int -> tactic
  val eqvt_strict_tac: Proof.context -> thm list -> string list -> int -> tactic
  
  val perm_simp_meth: thm list * string list -> Proof.context -> Method.method
  val perm_strict_simp_meth: thm list * string list -> Proof.context -> Method.method
  val args_parser: (thm list * string list) context_parser

  val trace_eqvt: bool Config.T
  val setup: theory -> theory
end;

(* 

- eqvt_tac and eqvt_strict_tac take a list of theorems
  which are first tried to simplify permutations

  the string list contains constants that should not be
  analysed (for example there is no raw eqvt-lemma for
  the constant The); therefore it should not be analysed 

- setting [[trace_eqvt = true]] switches on tracing 
  information  

*)

structure Nominal_Permeq: NOMINAL_PERMEQ =
struct

open Nominal_ThmDecls;

(* tracing infrastructure *)
val (trace_eqvt, trace_eqvt_setup) = Attrib.config_bool "trace_eqvt" (K false);

fun trace_enabled ctxt = Config.get ctxt trace_eqvt

fun trace_msg ctxt result = 
  let
    val lhs_str = Syntax.string_of_term ctxt (term_of (Thm.lhs_of result))
    val rhs_str = Syntax.string_of_term ctxt (term_of (Thm.rhs_of result))
  in
    warning (Pretty.string_of (Pretty.strs ["Rewriting", lhs_str, "to", rhs_str]))
  end

fun trace_conv ctxt conv ctrm =
  let
    val result = conv ctrm
  in
    if Thm.is_reflexive result 
    then result
    else (trace_msg ctxt result; result)
  end

(* this conversion always fails, but prints 
   out the analysed term  *)
fun trace_info_conv ctxt ctrm = 
  let
    val trm = term_of ctrm
    val _ = case (head_of trm) of 
        @{const "Trueprop"} => ()
      | _ => warning ("Analysing term " ^ Syntax.string_of_term ctxt trm)
  in
    Conv.no_conv ctrm
  end

(* conversion for applications *)
fun eqvt_apply_conv ctrm =
  case (term_of ctrm) of
    Const (@{const_name "permute"}, _) $ _ $ (_ $ _) =>
      let
        val (perm, t) = Thm.dest_comb ctrm
        val (_, p) = Thm.dest_comb perm
        val (f, x) = Thm.dest_comb t
        val a = ctyp_of_term x;
        val b = ctyp_of_term t;
        val ty_insts = map SOME [b, a]
        val term_insts = map SOME [p, f, x]                        
      in
        Drule.instantiate' ty_insts term_insts @{thm eqvt_apply}
      end
  | _ => Conv.no_conv ctrm

(* conversion for lambdas *)
fun eqvt_lambda_conv ctrm =
  case (term_of ctrm) of
    Const (@{const_name "permute"}, _) $ _ $ (Abs _) =>
      Conv.rewr_conv @{thm eqvt_lambda} ctrm
  | _ => Conv.no_conv ctrm


(* conversion that raises an error or prints a warning message, 
   if a permutation on a constant or application cannot be analysed *)

fun is_excluded excluded (Const (a, _)) = member (op=) excluded a 
  | is_excluded _ _ = false 

fun progress_info_conv ctxt strict_flag excluded ctrm =
  let
    fun msg trm =
      if is_excluded excluded trm then () else 
        (if strict_flag then error else warning) 
          ("Cannot solve equivariance for " ^ (Syntax.string_of_term ctxt trm))

    val _ = case (term_of ctrm) of
        Const (@{const_name "permute"}, _) $ _ $ (trm as Const _) => msg trm
      | Const (@{const_name "permute"}, _) $ _ $ (trm as _ $ _) => msg trm
      | _ => () 
  in
    Conv.all_conv ctrm 
  end

(* main conversion *) 
fun eqvt_conv ctxt strict_flag user_thms excluded ctrm =
  let
    val first_conv_wrapper = 
      if trace_enabled ctxt 
      then Conv.first_conv o (cons (trace_info_conv ctxt)) o (map (trace_conv ctxt))
      else Conv.first_conv

    val pre_thms = map safe_mk_equiv user_thms @ @{thms eqvt_bound} @ get_eqvts_raw_thms ctxt
    val post_thms = map safe_mk_equiv @{thms permute_pure}
  in
    first_conv_wrapper
      [ Conv.rewrs_conv pre_thms,
        eqvt_apply_conv,
        eqvt_lambda_conv,
        Conv.rewrs_conv post_thms,
        progress_info_conv ctxt strict_flag excluded
      ] ctrm
  end

(* the eqvt-tactics first eta-normalise goals in 
   order to avoid problems with inductions in the
   equivaraince command. *)

(* raises an error if some permutations cannot be eliminated *)
fun eqvt_strict_tac ctxt user_thms excluded = 
  CONVERSION (Conv.top_conv 
    (fn ctxt => Thm.eta_conversion then_conv (eqvt_conv ctxt true user_thms excluded)) ctxt)

(* prints a warning message if some permutations cannot be eliminated *)
fun eqvt_tac ctxt user_thms excluded = 
  CONVERSION (Conv.top_conv 
    (fn ctxt => Thm.eta_conversion then_conv (eqvt_conv ctxt false user_thms excluded)) ctxt)

(* setup of the configuration value *)
val setup =
  trace_eqvt_setup


(** methods **)
fun unless_more_args scan = Scan.unless (Scan.lift ((Args.$$$ "exclude") -- Args.colon)) scan

val add_thms_parser = Scan.optional (Scan.lift (Args.add -- Args.colon) |-- 
   Scan.repeat (unless_more_args Attrib.multi_thm) >> flat) [];

val exclude_consts_parser = Scan.optional (Scan.lift ((Args.$$$ "exclude") -- Args.colon) |-- 
  (Scan.repeat (Args.const true))) []

val args_parser =  add_thms_parser -- exclude_consts_parser 

fun perm_simp_meth (thms, consts) ctxt = 
  SIMPLE_METHOD (HEADGOAL (eqvt_tac ctxt thms consts))

fun perm_strict_simp_meth (thms, consts) ctxt = 
  SIMPLE_METHOD (HEADGOAL (eqvt_strict_tac ctxt thms consts))

end; (* structure *)