src/HOL/Tools/Nitpick/nitpick_mono.ML
author blanchet
Tue Oct 27 14:40:24 2009 +0100 (2009-10-27)
changeset 33232 f93390060bbe
parent 33192 08a39a957ed7
child 33571 3655e51f9958
permissions -rw-r--r--
internal renaming in Nitpick and fixed Kodkodi invokation on Linux;
renamed Nitpick's ML structures from NitpickXxx to Nitpick_Xxx and added KODKODI_JAVA_LIBRARY_PATH to LD_LIBRARY_PATH before invoking Kodkodi
     1 (*  Title:      HOL/Nitpick/Tools/nitpick_mono.ML
     2     Author:     Jasmin Blanchette, TU Muenchen
     3     Copyright   2009
     4 
     5 Monotonicity predicate for higher-order logic.
     6 *)
     7 
     8 signature NITPICK_MONO =
     9 sig
    10   type extended_context = Nitpick_HOL.extended_context
    11 
    12   val formulas_monotonic :
    13     extended_context -> typ -> term list -> term list -> term -> bool
    14 end;
    15 
    16 structure Nitpick_Mono : NITPICK_MONO =
    17 struct
    18 
    19 open Nitpick_Util
    20 open Nitpick_HOL
    21 
    22 type var = int
    23 
    24 datatype sign = Pos | Neg
    25 datatype sign_atom = S of sign | V of var
    26 
    27 type literal = var * sign
    28 
    29 datatype ctype =
    30   CAlpha |
    31   CFun of ctype * sign_atom * ctype |
    32   CPair of ctype * ctype |
    33   CType of string * ctype list |
    34   CRec of string * typ list
    35 
    36 type cdata =
    37   {ext_ctxt: extended_context,
    38    alpha_T: typ,
    39    max_fresh: int Unsynchronized.ref,
    40    datatype_cache: ((string * typ list) * ctype) list Unsynchronized.ref,
    41    constr_cache: (styp * ctype) list Unsynchronized.ref}
    42 
    43 exception CTYPE of string * ctype list
    44 
    45 (* string -> unit *)
    46 fun print_g (s : string) = ()
    47 
    48 (* var -> string *)
    49 val string_for_var = signed_string_of_int
    50 (* string -> var list -> string *)
    51 fun string_for_vars sep [] = "0\<^bsub>" ^ sep ^ "\<^esub>"
    52   | string_for_vars sep xs = space_implode sep (map string_for_var xs)
    53 fun subscript_string_for_vars sep xs =
    54   if null xs then "" else "\<^bsub>" ^ string_for_vars sep xs ^ "\<^esub>"
    55 
    56 (* sign -> string *)
    57 fun string_for_sign Pos = "+"
    58   | string_for_sign Neg = "-"
    59 
    60 (* sign -> sign -> sign *)
    61 fun xor sn1 sn2 = if sn1 = sn2 then Pos else Neg
    62 (* sign -> sign *)
    63 val negate = xor Neg
    64 
    65 (* sign_atom -> string *)
    66 fun string_for_sign_atom (S sn) = string_for_sign sn
    67   | string_for_sign_atom (V j) = string_for_var j
    68 
    69 (* literal -> string *)
    70 fun string_for_literal (x, sn) = string_for_var x ^ " = " ^ string_for_sign sn
    71 
    72 val bool_C = CType (@{type_name bool}, [])
    73 
    74 (* ctype -> bool *)
    75 fun is_CRec (CRec _) = true
    76   | is_CRec _ = false
    77 
    78 val no_prec = 100
    79 val prec_CFun = 1
    80 val prec_CPair = 2
    81 
    82 (* tuple_set -> int *)
    83 fun precedence_of_ctype (CFun _) = prec_CFun
    84   | precedence_of_ctype (CPair _) = prec_CPair
    85   | precedence_of_ctype _ = no_prec
    86 
    87 (* ctype -> string *)
    88 val string_for_ctype =
    89   let
    90     (* int -> ctype -> string *)
    91     fun aux outer_prec C =
    92       let
    93         val prec = precedence_of_ctype C
    94         val need_parens = (prec < outer_prec)
    95       in
    96         (if need_parens then "(" else "") ^
    97         (case C of
    98            CAlpha => "\<alpha>"
    99          | CFun (C1, a, C2) =>
   100            aux (prec + 1) C1 ^ " \<Rightarrow>\<^bsup>" ^
   101            string_for_sign_atom a ^ "\<^esup> " ^ aux prec C2
   102          | CPair (C1, C2) => aux (prec + 1) C1 ^ " \<times> " ^ aux prec C2
   103          | CType (s, []) =>
   104            if s mem [@{type_name prop}, @{type_name bool}] then "o" else s
   105          | CType (s, Cs) => "(" ^ commas (map (aux 0) Cs) ^ ") " ^ s
   106          | CRec (s, _) => "[" ^ s ^ "]") ^
   107         (if need_parens then ")" else "")
   108       end
   109   in aux 0 end
   110 
   111 (* ctype -> ctype list *)
   112 fun flatten_ctype (CPair (C1, C2)) = maps flatten_ctype [C1, C2]
   113   | flatten_ctype (CType (_, Cs)) = maps flatten_ctype Cs
   114   | flatten_ctype C = [C]
   115 
   116 (* extended_context -> typ -> cdata *)
   117 fun initial_cdata ext_ctxt alpha_T =
   118   ({ext_ctxt = ext_ctxt, alpha_T = alpha_T, max_fresh = Unsynchronized.ref 0,
   119     datatype_cache = Unsynchronized.ref [],
   120     constr_cache = Unsynchronized.ref []} : cdata)
   121 
   122 (* typ -> typ -> bool *)
   123 fun could_exist_alpha_subtype alpha_T (T as Type (_, Ts)) =
   124     T = alpha_T orelse (not (is_fp_iterator_type T)
   125                         andalso exists (could_exist_alpha_subtype alpha_T) Ts)
   126   | could_exist_alpha_subtype alpha_T T = (T = alpha_T)
   127 (* theory -> typ -> typ -> bool *)
   128 fun could_exist_alpha_sub_ctype _ (alpha_T as TFree _) =
   129     could_exist_alpha_subtype alpha_T
   130   | could_exist_alpha_sub_ctype thy alpha_T = equal alpha_T orf is_datatype thy
   131 
   132 (* ctype -> bool *)
   133 fun exists_alpha_sub_ctype CAlpha = true
   134   | exists_alpha_sub_ctype (CFun (C1, _, C2)) =
   135     exists exists_alpha_sub_ctype [C1, C2]
   136   | exists_alpha_sub_ctype (CPair (C1, C2)) =
   137     exists exists_alpha_sub_ctype [C1, C2]
   138   | exists_alpha_sub_ctype (CType (_, Cs)) = exists exists_alpha_sub_ctype Cs
   139   | exists_alpha_sub_ctype (CRec _) = true
   140 
   141 (* ctype -> bool *)
   142 fun exists_alpha_sub_ctype_fresh CAlpha = true
   143   | exists_alpha_sub_ctype_fresh (CFun (_, V _, _)) = true
   144   | exists_alpha_sub_ctype_fresh (CFun (_, _, C2)) =
   145     exists_alpha_sub_ctype_fresh C2
   146   | exists_alpha_sub_ctype_fresh (CPair (C1, C2)) =
   147     exists exists_alpha_sub_ctype_fresh [C1, C2]
   148   | exists_alpha_sub_ctype_fresh (CType (_, Cs)) =
   149     exists exists_alpha_sub_ctype_fresh Cs
   150   | exists_alpha_sub_ctype_fresh (CRec _) = true
   151 
   152 (* string * typ list -> ctype list -> ctype *)
   153 fun constr_ctype_for_binders z Cs =
   154   fold_rev (fn C => curry3 CFun C (S Neg)) Cs (CRec z)
   155 
   156 (* ((string * typ list) * ctype) list -> ctype list -> ctype -> ctype *)
   157 fun repair_ctype _ _ CAlpha = CAlpha
   158   | repair_ctype cache seen (CFun (C1, a, C2)) =
   159     CFun (repair_ctype cache seen C1, a, repair_ctype cache seen C2)
   160   | repair_ctype cache seen (CPair Cp) =
   161     CPair (pairself (repair_ctype cache seen) Cp)
   162   | repair_ctype cache seen (CType (s, Cs)) =
   163     CType (s, maps (flatten_ctype o repair_ctype cache seen) Cs)
   164   | repair_ctype cache seen (CRec (z as (s, _))) =
   165     case AList.lookup (op =) cache z |> the of
   166       CRec _ => CType (s, [])
   167     | C => if C mem seen then CType (s, [])
   168            else repair_ctype cache (C :: seen) C
   169 
   170 (* ((string * typ list) * ctype) list Unsynchronized.ref -> unit *)
   171 fun repair_datatype_cache cache =
   172   let
   173     (* (string * typ list) * ctype -> unit *)
   174     fun repair_one (z, C) =
   175       Unsynchronized.change cache
   176           (AList.update (op =) (z, repair_ctype (!cache) [] C))
   177   in List.app repair_one (rev (!cache)) end
   178 
   179 (* (typ * ctype) list -> (styp * ctype) list Unsynchronized.ref -> unit *)
   180 fun repair_constr_cache dtype_cache constr_cache =
   181   let
   182     (* styp * ctype -> unit *)
   183     fun repair_one (x, C) =
   184       Unsynchronized.change constr_cache
   185           (AList.update (op =) (x, repair_ctype dtype_cache [] C))
   186   in List.app repair_one (!constr_cache) end
   187 
   188 (* cdata -> typ -> ctype *)
   189 fun fresh_ctype_for_type ({ext_ctxt as {thy, ...}, alpha_T, max_fresh,
   190                            datatype_cache, constr_cache, ...} : cdata) =
   191   let
   192     (* typ -> typ -> ctype *)
   193     fun do_fun T1 T2 =
   194       let
   195         val C1 = do_type T1
   196         val C2 = do_type T2
   197         val a = if is_boolean_type (body_type T2)
   198                    andalso exists_alpha_sub_ctype_fresh C1 then
   199                   V (Unsynchronized.inc max_fresh)
   200                 else
   201                   S Neg
   202       in CFun (C1, a, C2) end
   203     (* typ -> ctype *)
   204     and do_type T =
   205       if T = alpha_T then
   206         CAlpha
   207       else case T of
   208         Type ("fun", [T1, T2]) => do_fun T1 T2
   209       | Type (@{type_name fun_box}, [T1, T2]) => do_fun T1 T2
   210       | Type ("*", [T1, T2]) => CPair (pairself do_type (T1, T2))
   211       | Type (z as (s, _)) =>
   212         if could_exist_alpha_sub_ctype thy alpha_T T then
   213           case AList.lookup (op =) (!datatype_cache) z of
   214             SOME C => C
   215           | NONE =>
   216             let
   217               val _ = Unsynchronized.change datatype_cache (cons (z, CRec z))
   218               val xs = datatype_constrs thy T
   219               val (all_Cs, constr_Cs) =
   220                 fold_rev (fn (_, T') => fn (all_Cs, constr_Cs) =>
   221                              let
   222                                val binder_Cs = map do_type (binder_types T')
   223                                val new_Cs = filter exists_alpha_sub_ctype_fresh
   224                                                    binder_Cs
   225                                val constr_C = constr_ctype_for_binders z
   226                                                                        binder_Cs
   227                              in
   228                                (union (op =) new_Cs all_Cs,
   229                                 constr_C :: constr_Cs)
   230                              end)
   231                          xs ([], [])
   232               val C = CType (s, all_Cs)
   233               val _ = Unsynchronized.change datatype_cache
   234                           (AList.update (op =) (z, C))
   235               val _ = Unsynchronized.change constr_cache
   236                           (append (xs ~~ constr_Cs))
   237             in
   238               if forall (not o is_CRec o snd) (!datatype_cache) then
   239                 (repair_datatype_cache datatype_cache;
   240                  repair_constr_cache (!datatype_cache) constr_cache;
   241                  AList.lookup (op =) (!datatype_cache) z |> the)
   242               else
   243                 C
   244             end
   245         else
   246           CType (s, [])
   247       | _ => CType (Refute.string_of_typ T, [])
   248   in do_type end
   249 
   250 (* ctype -> ctype list *)
   251 fun prodC_factors (CPair (C1, C2)) = maps prodC_factors [C1, C2]
   252   | prodC_factors C = [C]
   253 (* ctype -> ctype list * ctype *)
   254 fun curried_strip_ctype (CFun (C1, S Neg, C2)) =
   255     curried_strip_ctype C2 |>> append (prodC_factors C1)
   256   | curried_strip_ctype C = ([], C)
   257 (* string -> ctype -> ctype *)
   258 fun sel_ctype_from_constr_ctype s C =
   259   let val (arg_Cs, dataC) = curried_strip_ctype C in
   260     CFun (dataC, S Neg,
   261           case sel_no_from_name s of ~1 => bool_C | n => nth arg_Cs n)
   262   end
   263 
   264 (* cdata -> styp -> ctype *)
   265 fun ctype_for_constr (cdata as {ext_ctxt as {thy, ...}, alpha_T, constr_cache,
   266                                 ...}) (x as (_, T)) =
   267   if could_exist_alpha_sub_ctype thy alpha_T T then
   268     case AList.lookup (op =) (!constr_cache) x of
   269       SOME C => C
   270     | NONE => (fresh_ctype_for_type cdata (body_type T);
   271                AList.lookup (op =) (!constr_cache) x |> the)
   272   else
   273     fresh_ctype_for_type cdata T
   274 fun ctype_for_sel (cdata as {ext_ctxt, ...}) (x as (s, _)) =
   275   x |> boxed_constr_for_sel ext_ctxt |> ctype_for_constr cdata
   276     |> sel_ctype_from_constr_ctype s
   277 
   278 (* literal list -> ctype -> ctype *)
   279 fun instantiate_ctype lits =
   280   let
   281     (* ctype -> ctype *)
   282     fun aux CAlpha = CAlpha
   283       | aux (CFun (C1, V x, C2)) =
   284         let
   285           val a = case AList.lookup (op =) lits x of
   286                     SOME sn => S sn
   287                   | NONE => V x
   288         in CFun (aux C1, a, aux C2) end
   289       | aux (CFun (C1, a, C2)) = CFun (aux C1, a, aux C2)
   290       | aux (CPair Cp) = CPair (pairself aux Cp)
   291       | aux (CType (s, Cs)) = CType (s, map aux Cs)
   292       | aux (CRec z) = CRec z
   293   in aux end
   294 
   295 datatype comp_op = Eq | Leq
   296 
   297 type comp = sign_atom * sign_atom * comp_op * var list
   298 type sign_expr = literal list
   299 
   300 datatype constraint_set =
   301   UnsolvableCSet |
   302   CSet of literal list * comp list * sign_expr list
   303 
   304 (* comp_op -> string *)
   305 fun string_for_comp_op Eq = "="
   306   | string_for_comp_op Leq = "\<le>"
   307 
   308 (* sign_expr -> string *)
   309 fun string_for_sign_expr [] = "\<bot>"
   310   | string_for_sign_expr lits =
   311     space_implode " \<or> " (map string_for_literal lits)
   312 
   313 (* constraint_set *)
   314 val slack = CSet ([], [], [])
   315 
   316 (* literal -> literal list option -> literal list option *)
   317 fun do_literal _ NONE = NONE
   318   | do_literal (x, sn) (SOME lits) =
   319     case AList.lookup (op =) lits x of
   320       SOME sn' => if sn = sn' then SOME lits else NONE
   321     | NONE => SOME ((x, sn) :: lits)
   322 
   323 (* comp_op -> var list -> sign_atom -> sign_atom -> literal list * comp list
   324    -> (literal list * comp list) option *)
   325 fun do_sign_atom_comp Eq [] a1 a2 (accum as (lits, comps)) =
   326     (case (a1, a2) of
   327        (S sn1, S sn2) => if sn1 = sn2 then SOME accum else NONE
   328      | (V x1, S sn2) =>
   329        Option.map (rpair comps) (do_literal (x1, sn2) (SOME lits))
   330      | (V _, V _) => SOME (lits, insert (op =) (a1, a2, Eq, []) comps)
   331      | _ => do_sign_atom_comp Eq [] a2 a1 accum)
   332   | do_sign_atom_comp Leq [] a1 a2 (accum as (lits, comps)) =
   333     (case (a1, a2) of
   334        (_, S Neg) => SOME accum
   335      | (S Pos, _) => SOME accum
   336      | (S Neg, S Pos) => NONE
   337      | (V _, V _) => SOME (lits, insert (op =) (a1, a2, Leq, []) comps)
   338      | _ => do_sign_atom_comp Eq [] a1 a2 accum)
   339   | do_sign_atom_comp cmp xs a1 a2 (accum as (lits, comps)) =
   340     SOME (lits, insert (op =) (a1, a2, cmp, xs) comps)
   341 
   342 (* comp -> var list -> ctype -> ctype -> (literal list * comp list) option
   343    -> (literal list * comp list) option *)
   344 fun do_ctype_comp _ _ _ _ NONE = NONE
   345   | do_ctype_comp _ _ CAlpha CAlpha accum = accum
   346   | do_ctype_comp Eq xs (CFun (C11, a1, C12)) (CFun (C21, a2, C22))
   347                   (SOME accum) =
   348      accum |> do_sign_atom_comp Eq xs a1 a2 |> do_ctype_comp Eq xs C11 C21
   349            |> do_ctype_comp Eq xs C12 C22
   350   | do_ctype_comp Leq xs (CFun (C11, a1, C12)) (CFun (C21, a2, C22))
   351                   (SOME accum) =
   352     (if exists_alpha_sub_ctype C11 then
   353        accum |> do_sign_atom_comp Leq xs a1 a2
   354              |> do_ctype_comp Leq xs C21 C11
   355              |> (case a2 of
   356                    S Neg => I
   357                  | S Pos => do_ctype_comp Leq xs C11 C21
   358                  | V x => do_ctype_comp Leq (x :: xs) C11 C21)
   359      else
   360        SOME accum)
   361     |> do_ctype_comp Leq xs C12 C22
   362   | do_ctype_comp cmp xs (C1 as CPair (C11, C12)) (C2 as CPair (C21, C22))
   363                   accum =
   364     (accum |> fold (uncurry (do_ctype_comp cmp xs)) [(C11, C21), (C12, C22)]
   365      handle Library.UnequalLengths =>
   366             raise CTYPE ("Nitpick_Mono.do_ctype_comp", [C1, C2]))
   367   | do_ctype_comp cmp xs (CType _) (CType _) accum =
   368     accum (* no need to compare them thanks to the cache *)
   369   | do_ctype_comp _ _ C1 C2 _ =
   370     raise CTYPE ("Nitpick_Mono.do_ctype_comp", [C1, C2])
   371 
   372 (* comp_op -> ctype -> ctype -> constraint_set -> constraint_set *)
   373 fun add_ctype_comp _ _ _ UnsolvableCSet = UnsolvableCSet
   374   | add_ctype_comp cmp C1 C2 (CSet (lits, comps, sexps)) =
   375     (print_g ("*** Add " ^ string_for_ctype C1 ^ " " ^ string_for_comp_op cmp ^
   376               " " ^ string_for_ctype C2);
   377      case do_ctype_comp cmp [] C1 C2 (SOME (lits, comps)) of
   378        NONE => (print_g "**** Unsolvable"; UnsolvableCSet)
   379      | SOME (lits, comps) => CSet (lits, comps, sexps))
   380 
   381 (* ctype -> ctype -> constraint_set -> constraint_set *)
   382 val add_ctypes_equal = add_ctype_comp Eq
   383 val add_is_sub_ctype = add_ctype_comp Leq
   384 
   385 (* sign -> sign_expr -> ctype -> (literal list * sign_expr list) option
   386    -> (literal list * sign_expr list) option *)
   387 fun do_notin_ctype_fv _ _ _ NONE = NONE
   388   | do_notin_ctype_fv Neg _ CAlpha accum = accum
   389   | do_notin_ctype_fv Pos [] CAlpha _ = NONE
   390   | do_notin_ctype_fv Pos [(x, sn)] CAlpha (SOME (lits, sexps)) =
   391     SOME lits |> do_literal (x, sn) |> Option.map (rpair sexps)
   392   | do_notin_ctype_fv Pos sexp CAlpha (SOME (lits, sexps)) =
   393     SOME (lits, insert (op =) sexp sexps)
   394   | do_notin_ctype_fv sn sexp (CFun (C1, S sn', C2)) accum =
   395     accum |> (if sn' = Pos andalso sn = Pos then do_notin_ctype_fv Pos sexp C1
   396               else I)
   397           |> (if sn' = Neg orelse sn = Pos then do_notin_ctype_fv Neg sexp C1
   398               else I)
   399           |> do_notin_ctype_fv sn sexp C2
   400   | do_notin_ctype_fv Pos sexp (CFun (C1, V x, C2)) accum =
   401     accum |> (case do_literal (x, Neg) (SOME sexp) of
   402                 NONE => I
   403               | SOME sexp' => do_notin_ctype_fv Pos sexp' C1)
   404           |> do_notin_ctype_fv Neg sexp C1
   405           |> do_notin_ctype_fv Pos sexp C2
   406   | do_notin_ctype_fv Neg sexp (CFun (C1, V x, C2)) accum =
   407     accum |> (case do_literal (x, Pos) (SOME sexp) of
   408                 NONE => I
   409               | SOME sexp' => do_notin_ctype_fv Pos sexp' C1)
   410           |> do_notin_ctype_fv Neg sexp C2
   411   | do_notin_ctype_fv sn sexp (CPair (C1, C2)) accum =
   412     accum |> fold (do_notin_ctype_fv sn sexp) [C1, C2]
   413   | do_notin_ctype_fv sn sexp (CType (_, Cs)) accum =
   414     accum |> fold (do_notin_ctype_fv sn sexp) Cs
   415   | do_notin_ctype_fv _ _ C _ =
   416     raise CTYPE ("Nitpick_Mono.do_notin_ctype_fv", [C])
   417 
   418 (* sign -> ctype -> constraint_set -> constraint_set *)
   419 fun add_notin_ctype_fv _ _ UnsolvableCSet = UnsolvableCSet
   420   | add_notin_ctype_fv sn C (CSet (lits, comps, sexps)) =
   421     (print_g ("*** Add " ^ string_for_ctype C ^ " is right-" ^
   422               (case sn of Neg => "unique" | Pos => "total") ^ ".");
   423      case do_notin_ctype_fv sn [] C (SOME (lits, sexps)) of
   424        NONE => (print_g "**** Unsolvable"; UnsolvableCSet)
   425      | SOME (lits, sexps) => CSet (lits, comps, sexps))
   426 
   427 (* ctype -> constraint_set -> constraint_set *)
   428 val add_ctype_is_right_unique = add_notin_ctype_fv Neg
   429 val add_ctype_is_right_total = add_notin_ctype_fv Pos
   430 
   431 (* constraint_set -> constraint_set -> constraint_set *)
   432 fun unite (CSet (lits1, comps1, sexps1)) (CSet (lits2, comps2, sexps2)) =
   433     (case SOME lits1 |> fold do_literal lits2 of
   434        NONE => (print_g "**** Unsolvable"; UnsolvableCSet)
   435      | SOME lits => CSet (lits, comps1 @ comps2, sexps1 @ sexps2))
   436   | unite _ _ = UnsolvableCSet
   437 
   438 (* sign -> bool *)
   439 fun bool_from_sign Pos = false
   440   | bool_from_sign Neg = true
   441 (* bool -> sign *)
   442 fun sign_from_bool false = Pos
   443   | sign_from_bool true = Neg
   444 
   445 (* literal -> PropLogic.prop_formula *)
   446 fun prop_for_literal (x, sn) =
   447   (not (bool_from_sign sn) ? PropLogic.Not) (PropLogic.BoolVar x)
   448 (* sign_atom -> PropLogic.prop_formula *)
   449 fun prop_for_sign_atom_eq (S sn', sn) =
   450     if sn = sn' then PropLogic.True else PropLogic.False
   451   | prop_for_sign_atom_eq (V x, sn) = prop_for_literal (x, sn)
   452 (* sign_expr -> PropLogic.prop_formula *)
   453 fun prop_for_sign_expr xs = PropLogic.exists (map prop_for_literal xs)
   454 (* var list -> sign -> PropLogic.prop_formula *)
   455 fun prop_for_exists_eq xs sn =
   456   PropLogic.exists (map (fn x => prop_for_literal (x, sn)) xs)
   457 (* comp -> PropLogic.prop_formula *)
   458 fun prop_for_comp (a1, a2, Eq, []) =
   459     PropLogic.SAnd (prop_for_comp (a1, a2, Leq, []),
   460                     prop_for_comp (a2, a1, Leq, []))
   461   | prop_for_comp (a1, a2, Leq, []) =
   462     PropLogic.SOr (prop_for_sign_atom_eq (a1, Pos),
   463                    prop_for_sign_atom_eq (a2, Neg))
   464   | prop_for_comp (a1, a2, cmp, xs) =
   465     PropLogic.SOr (prop_for_exists_eq xs Neg, prop_for_comp (a1, a2, cmp, []))
   466 
   467 (* var -> (int -> bool option) -> literal list -> literal list *)
   468 fun literals_from_assignments max_var asgns lits =
   469   fold (fn x => fn accum =>
   470            if AList.defined (op =) lits x then
   471              accum
   472            else case asgns x of
   473              SOME b => (x, sign_from_bool b) :: accum
   474            | NONE => accum) (max_var downto 1) lits
   475 
   476 (* literal list -> sign_atom -> sign option *)
   477 fun lookup_sign_atom _ (S sn) = SOME sn
   478   | lookup_sign_atom lit (V x) = AList.lookup (op =) lit x
   479 
   480 (* comp -> string *)
   481 fun string_for_comp (a1, a2, cmp, xs) =
   482   string_for_sign_atom a1 ^ " " ^ string_for_comp_op cmp ^
   483   subscript_string_for_vars " \<and> " xs ^ " " ^ string_for_sign_atom a2
   484 
   485 (* literal list -> comp list -> sign_expr list -> unit *)
   486 fun print_problem lits comps sexps =
   487   print_g ("*** Problem:\n" ^ cat_lines (map string_for_literal lits @
   488                                          map string_for_comp comps @
   489                                          map string_for_sign_expr sexps))
   490 
   491 (* literal list -> unit *)
   492 fun print_solution lits =
   493   let val (pos, neg) = List.partition (equal Pos o snd) lits in
   494     print_g ("*** Solution:\n" ^
   495              "+: " ^ commas (map (string_for_var o fst) pos) ^ "\n" ^
   496              "-: " ^ commas (map (string_for_var o fst) neg))
   497   end
   498 
   499 (* var -> constraint_set -> literal list list option *)
   500 fun solve _ UnsolvableCSet = (print_g "*** Problem: Unsolvable"; NONE)
   501   | solve max_var (CSet (lits, comps, sexps)) =
   502     let
   503       val _ = print_problem lits comps sexps
   504       val prop = PropLogic.all (map prop_for_literal lits @
   505                                 map prop_for_comp comps @
   506                                 map prop_for_sign_expr sexps)
   507     in
   508       case silence (SatSolver.invoke_solver "dpll") prop of
   509         SatSolver.SATISFIABLE asgns =>
   510         SOME (literals_from_assignments max_var asgns lits
   511               |> tap print_solution)
   512       | _ => NONE
   513     end
   514 
   515 (* var -> constraint_set -> bool *)
   516 val is_solvable = is_some oo solve
   517 
   518 type ctype_schema = ctype * constraint_set
   519 type ctype_context =
   520   {bounds: ctype list,
   521    frees: (styp * ctype) list,
   522    consts: (styp * ctype_schema) list}
   523 
   524 type accumulator = ctype_context * constraint_set
   525 
   526 val initial_gamma = {bounds = [], frees = [], consts = []}
   527 val unsolvable_accum = (initial_gamma, UnsolvableCSet)
   528 
   529 (* ctype -> ctype_context -> ctype_context *)
   530 fun push_bound C {bounds, frees, consts} =
   531   {bounds = C :: bounds, frees = frees, consts = consts}
   532 (* ctype_context -> ctype_context *)
   533 fun pop_bound {bounds, frees, consts} =
   534   {bounds = tl bounds, frees = frees, consts = consts}
   535   handle List.Empty => initial_gamma
   536 
   537 (* cdata -> term -> accumulator -> ctype * accumulator *)
   538 fun consider_term (cdata as {ext_ctxt as {ctxt, thy, def_table, ...}, alpha_T,
   539                              max_fresh, ...}) =
   540   let
   541     (* typ -> ctype *)
   542     val ctype_for = fresh_ctype_for_type cdata
   543     (* ctype -> ctype *)
   544     fun pos_set_ctype_for_dom C =
   545       CFun (C, S (if exists_alpha_sub_ctype C then Pos else Neg), bool_C)
   546     (* typ -> accumulator -> ctype * accumulator *)
   547     fun do_quantifier T (gamma, cset) =
   548       let
   549         val abs_C = ctype_for (domain_type (domain_type T))
   550         val body_C = ctype_for (range_type T)
   551       in
   552         (CFun (CFun (abs_C, S Neg, body_C), S Neg, body_C),
   553          (gamma, cset |> add_ctype_is_right_total abs_C))
   554       end
   555     fun do_equals T (gamma, cset) =
   556       let val C = ctype_for (domain_type T) in
   557         (CFun (C, S Neg, CFun (C, S Neg, ctype_for (nth_range_type 2 T))),
   558          (gamma, cset |> add_ctype_is_right_unique C))
   559       end
   560     fun do_robust_set_operation T (gamma, cset) =
   561       let
   562         val set_T = domain_type T
   563         val C1 = ctype_for set_T
   564         val C2 = ctype_for set_T
   565         val C3 = ctype_for set_T
   566       in
   567         (CFun (C1, S Neg, CFun (C2, S Neg, C3)),
   568          (gamma, cset |> add_is_sub_ctype C1 C3 |> add_is_sub_ctype C2 C3))
   569       end
   570     fun do_fragile_set_operation T (gamma, cset) =
   571       let
   572         val set_T = domain_type T
   573         val set_C = ctype_for set_T
   574         (* typ -> ctype *)
   575         fun custom_ctype_for (T as Type ("fun", [T1, T2])) =
   576             if T = set_T then set_C
   577             else CFun (custom_ctype_for T1, S Neg, custom_ctype_for T2)
   578           | custom_ctype_for T = ctype_for T
   579       in
   580         (custom_ctype_for T, (gamma, cset |> add_ctype_is_right_unique set_C))
   581       end
   582     (* typ -> accumulator -> ctype * accumulator *)
   583     fun do_pair_constr T accum =
   584       case ctype_for (nth_range_type 2 T) of
   585         C as CPair (a_C, b_C) =>
   586         (CFun (a_C, S Neg, CFun (b_C, S Neg, C)), accum)
   587       | C => raise CTYPE ("Nitpick_Mono.consider_term.do_pair_constr", [C])
   588     (* int -> typ -> accumulator -> ctype * accumulator *)
   589     fun do_nth_pair_sel n T =
   590       case ctype_for (domain_type T) of
   591         C as CPair (a_C, b_C) =>
   592         pair (CFun (C, S Neg, if n = 0 then a_C else b_C))
   593       | C => raise CTYPE ("Nitpick_Mono.consider_term.do_nth_pair_sel", [C])
   594     val unsolvable = (CType ("unsolvable", []), unsolvable_accum)
   595     (* typ -> term -> accumulator -> ctype * accumulator *)
   596     fun do_bounded_quantifier abs_T bound_t body_t accum =
   597       let
   598         val abs_C = ctype_for abs_T
   599         val (bound_C, accum) = accum |>> push_bound abs_C |> do_term bound_t
   600         val expected_bound_C = pos_set_ctype_for_dom abs_C
   601       in
   602         accum ||> add_ctypes_equal expected_bound_C bound_C |> do_term body_t
   603               ||> apfst pop_bound
   604       end
   605     (* term -> accumulator -> ctype * accumulator *)
   606     and do_term _ (_, UnsolvableCSet) = unsolvable
   607       | do_term t (accum as (gamma as {bounds, frees, consts}, cset)) =
   608         (case t of
   609            Const (x as (s, T)) =>
   610            (case AList.lookup (op =) consts x of
   611               SOME (C, cset') => (C, (gamma, cset |> unite cset'))
   612             | NONE =>
   613               if not (could_exist_alpha_subtype alpha_T T) then
   614                 (ctype_for T, accum)
   615               else case s of
   616                 @{const_name all} => do_quantifier T accum
   617               | @{const_name "=="} => do_equals T accum
   618               | @{const_name All} => do_quantifier T accum
   619               | @{const_name Ex} => do_quantifier T accum
   620               | @{const_name "op ="} => do_equals T accum
   621               | @{const_name The} => (print_g "*** The"; unsolvable)
   622               | @{const_name Eps} => (print_g "*** Eps"; unsolvable)
   623               | @{const_name If} =>
   624                 do_robust_set_operation (range_type T) accum
   625                 |>> curry3 CFun bool_C (S Neg)
   626               | @{const_name Pair} => do_pair_constr T accum
   627               | @{const_name fst} => do_nth_pair_sel 0 T accum
   628               | @{const_name snd} => do_nth_pair_sel 1 T accum 
   629               | @{const_name Id} =>
   630                 (CFun (ctype_for (domain_type T), S Neg, bool_C), accum)
   631               | @{const_name insert} =>
   632                 let
   633                   val set_T = domain_type (range_type T)
   634                   val C1 = ctype_for (domain_type set_T)
   635                   val C1' = pos_set_ctype_for_dom C1
   636                   val C2 = ctype_for set_T
   637                   val C3 = ctype_for set_T
   638                 in
   639                   (CFun (C1, S Neg, CFun (C2, S Neg, C3)),
   640                    (gamma, cset |> add_ctype_is_right_unique C1
   641                                 |> add_is_sub_ctype C1' C3
   642                                 |> add_is_sub_ctype C2 C3))
   643                 end
   644               | @{const_name converse} =>
   645                 let
   646                   val x = Unsynchronized.inc max_fresh
   647                   (* typ -> ctype *)
   648                   fun ctype_for_set T =
   649                     CFun (ctype_for (domain_type T), V x, bool_C)
   650                   val ab_set_C = domain_type T |> ctype_for_set
   651                   val ba_set_C = range_type T |> ctype_for_set
   652                 in (CFun (ab_set_C, S Neg, ba_set_C), accum) end
   653               | @{const_name trancl} => do_fragile_set_operation T accum
   654               | @{const_name rtrancl} => (print_g "*** rtrancl"; unsolvable)
   655               | @{const_name lower_semilattice_fun_inst.inf_fun} =>
   656                 do_robust_set_operation T accum
   657               | @{const_name upper_semilattice_fun_inst.sup_fun} =>
   658                 do_robust_set_operation T accum
   659               | @{const_name finite} =>
   660                 let val C1 = ctype_for (domain_type (domain_type T)) in
   661                   (CFun (pos_set_ctype_for_dom C1, S Neg, bool_C), accum)
   662                 end
   663               | @{const_name rel_comp} =>
   664                 let
   665                   val x = Unsynchronized.inc max_fresh
   666                   (* typ -> ctype *)
   667                   fun ctype_for_set T =
   668                     CFun (ctype_for (domain_type T), V x, bool_C)
   669                   val bc_set_C = domain_type T |> ctype_for_set
   670                   val ab_set_C = domain_type (range_type T) |> ctype_for_set
   671                   val ac_set_C = nth_range_type 2 T |> ctype_for_set
   672                 in
   673                   (CFun (bc_set_C, S Neg, CFun (ab_set_C, S Neg, ac_set_C)),
   674                    accum)
   675                 end
   676               | @{const_name image} =>
   677                 let
   678                   val a_C = ctype_for (domain_type (domain_type T))
   679                   val b_C = ctype_for (range_type (domain_type T))
   680                 in
   681                   (CFun (CFun (a_C, S Neg, b_C), S Neg,
   682                          CFun (pos_set_ctype_for_dom a_C, S Neg,
   683                                pos_set_ctype_for_dom b_C)), accum)
   684                 end
   685               | @{const_name Sigma} =>
   686                 let
   687                   val x = Unsynchronized.inc max_fresh
   688                   (* typ -> ctype *)
   689                   fun ctype_for_set T =
   690                     CFun (ctype_for (domain_type T), V x, bool_C)
   691                   val a_set_T = domain_type T
   692                   val a_C = ctype_for (domain_type a_set_T)
   693                   val b_set_C = ctype_for_set (range_type (domain_type
   694                                                                (range_type T)))
   695                   val a_set_C = ctype_for_set a_set_T
   696                   val a_to_b_set_C = CFun (a_C, S Neg, b_set_C)
   697                   val ab_set_C = ctype_for_set (nth_range_type 2 T)
   698                 in
   699                   (CFun (a_set_C, S Neg, CFun (a_to_b_set_C, S Neg, ab_set_C)),
   700                    accum)
   701                 end
   702               | @{const_name minus_fun_inst.minus_fun} =>
   703                 let
   704                   val set_T = domain_type T
   705                   val left_set_C = ctype_for set_T
   706                   val right_set_C = ctype_for set_T
   707                 in
   708                   (CFun (left_set_C, S Neg,
   709                          CFun (right_set_C, S Neg, left_set_C)),
   710                    (gamma, cset |> add_ctype_is_right_unique right_set_C
   711                           (* FIXME: |> add_is_sub_ctype right_set_C left_set_C *)))
   712                 end
   713               | @{const_name ord_fun_inst.less_eq_fun} =>
   714                 do_fragile_set_operation T accum
   715               | @{const_name Tha} =>
   716                 let
   717                   val a_C = ctype_for (domain_type (domain_type T))
   718                   val a_set_C = pos_set_ctype_for_dom a_C
   719                 in (CFun (a_set_C, S Neg, a_C), accum) end
   720               | @{const_name FunBox} =>
   721                 let val dom_C = ctype_for (domain_type T) in
   722                   (CFun (dom_C, S Neg, dom_C), accum)
   723                 end
   724               | _ => if is_sel s then
   725                        if constr_name_for_sel_like s = @{const_name FunBox} then
   726                          let val dom_C = ctype_for (domain_type T) in
   727                            (CFun (dom_C, S Neg, dom_C), accum)
   728                          end
   729                        else
   730                          (ctype_for_sel cdata x, accum)
   731                      else if is_constr thy x then
   732                        (ctype_for_constr cdata x, accum)
   733                      else if is_built_in_const true x then
   734                        case def_of_const thy def_table x of
   735                          SOME t' => do_term t' accum
   736                        | NONE => (print_g ("*** built-in " ^ s); unsolvable)
   737                      else
   738                        (ctype_for T, accum))
   739          | Free (x as (_, T)) =>
   740            (case AList.lookup (op =) frees x of
   741               SOME C => (C, accum)
   742             | NONE =>
   743               let val C = ctype_for T in
   744                 (C, ({bounds = bounds, frees = (x, C) :: frees,
   745                       consts = consts}, cset))
   746               end)
   747          | Var _ => (print_g "*** Var"; unsolvable)
   748          | Bound j => (nth bounds j, accum)
   749          | Abs (_, T, @{const False}) => (ctype_for (T --> bool_T), accum)
   750          | Abs (s, T, t') =>
   751            let
   752              val C = ctype_for T
   753              val (C', accum) = do_term t' (accum |>> push_bound C)
   754            in (CFun (C, S Neg, C'), accum |>> pop_bound) end
   755          | Const (@{const_name All}, _)
   756            $ Abs (_, T', @{const "op -->"} $ (t1 $ Bound 0) $ t2) =>
   757            do_bounded_quantifier T' t1 t2 accum
   758          | Const (@{const_name Ex}, _)
   759            $ Abs (_, T', @{const "op &"} $ (t1 $ Bound 0) $ t2) =>
   760            do_bounded_quantifier T' t1 t2 accum
   761          | Const (@{const_name Let}, _) $ t1 $ t2 =>
   762            do_term (betapply (t2, t1)) accum
   763          | t1 $ t2 =>
   764            let
   765              val (C1, accum) = do_term t1 accum
   766              val (C2, accum) = do_term t2 accum
   767            in
   768              case accum of
   769                (_, UnsolvableCSet) => unsolvable
   770              | _ => case C1 of
   771                       CFun (C11, _, C12) =>
   772                       (C12, accum ||> add_is_sub_ctype C2 C11)
   773                     | _ => raise CTYPE ("Nitpick_Mono.consider_term.do_term \
   774                                         \(op $)", [C1])
   775            end)
   776         |> tap (fn (C, _) =>
   777                    print_g ("  \<Gamma> \<turnstile> " ^
   778                             Syntax.string_of_term ctxt t ^ " : " ^
   779                             string_for_ctype C))
   780   in do_term end
   781 
   782 (* cdata -> sign -> term -> accumulator -> accumulator *)
   783 fun consider_general_formula (cdata as {ext_ctxt as {ctxt, ...}, ...}) =
   784   let
   785     (* typ -> ctype *)
   786     val ctype_for = fresh_ctype_for_type cdata
   787     (* term -> accumulator -> ctype * accumulator *)
   788     val do_term = consider_term cdata
   789     (* term -> accumulator -> accumulator *)
   790     val do_boolean_term = snd oo do_term
   791     (* sign -> term -> accumulator -> accumulator *)
   792     fun do_formula _ _ (_, UnsolvableCSet) = unsolvable_accum
   793       | do_formula sn t (accum as (gamma as {bounds, frees, consts}, cset)) =
   794         let
   795           (* term -> accumulator -> accumulator *)
   796           val do_co_formula = do_formula sn
   797           val do_contra_formula = do_formula (negate sn)
   798           (* string -> typ -> term -> accumulator *)
   799           fun do_quantifier quant_s abs_T body_t =
   800             let
   801               val abs_C = ctype_for abs_T
   802               val side_cond = ((sn = Neg) = (quant_s = @{const_name Ex}))
   803               val cset = cset |> side_cond ? add_ctype_is_right_total abs_C
   804             in
   805               (gamma |> push_bound abs_C, cset) |> do_co_formula body_t
   806                                                 |>> pop_bound
   807             end
   808           (* typ -> term -> accumulator *)
   809           fun do_bounded_quantifier abs_T body_t =
   810             accum |>> push_bound (ctype_for abs_T) |> do_co_formula body_t
   811                   |>> pop_bound
   812           (* term -> term -> accumulator *)
   813           fun do_equals t1 t2 =
   814             case sn of
   815               Pos => do_boolean_term t accum
   816             | Neg => let
   817                        val (C1, accum) = do_term t1 accum
   818                        val (C2, accum) = do_term t2 accum
   819                      in accum (* FIXME: ||> add_ctypes_equal C1 C2 *) end
   820         in
   821           case t of
   822             Const (s0 as @{const_name all}, _) $ Abs (_, T1, t1) =>
   823             do_quantifier s0 T1 t1
   824           | Const (@{const_name "=="}, _) $ t1 $ t2 => do_equals t1 t2
   825           | @{const "==>"} $ t1 $ t2 =>
   826             accum |> do_contra_formula t1 |> do_co_formula t2
   827           | @{const Trueprop} $ t1 => do_co_formula t1 accum
   828           | @{const Not} $ t1 => do_contra_formula t1 accum
   829           | Const (@{const_name All}, _)
   830             $ Abs (_, T1, t1 as @{const "op -->"} $ (_ $ Bound 0) $ _) =>
   831             do_bounded_quantifier T1 t1
   832           | Const (s0 as @{const_name All}, _) $ Abs (_, T1, t1) =>
   833             do_quantifier s0 T1 t1
   834           | Const (@{const_name Ex}, _)
   835             $ Abs (_, T1, t1 as @{const "op &"} $ (_ $ Bound 0) $ _) =>
   836             do_bounded_quantifier T1 t1
   837           | Const (s0 as @{const_name Ex}, _) $ Abs (_, T1, t1) =>
   838             do_quantifier s0 T1 t1
   839           | Const (@{const_name "op ="}, _) $ t1 $ t2 => do_equals t1 t2
   840           | @{const "op &"} $ t1 $ t2 =>
   841             accum |> do_co_formula t1 |> do_co_formula t2
   842           | @{const "op |"} $ t1 $ t2 =>
   843             accum |> do_co_formula t1 |> do_co_formula t2
   844           | @{const "op -->"} $ t1 $ t2 =>
   845             accum |> do_contra_formula t1 |> do_co_formula t2
   846           | Const (@{const_name If}, _) $ t1 $ t2 $ t3 =>
   847             accum |> do_boolean_term t1 |> do_co_formula t2 |> do_co_formula t3
   848           | Const (@{const_name Let}, _) $ t1 $ t2 =>
   849             do_co_formula (betapply (t2, t1)) accum
   850           | _ => do_boolean_term t accum
   851         end
   852         |> tap (fn _ => print_g ("\<Gamma> \<turnstile> " ^
   853                                  Syntax.string_of_term ctxt t ^
   854                                  " : o\<^sup>" ^ string_for_sign sn))
   855   in do_formula end
   856 
   857 (* The harmless axiom optimization below is somewhat too aggressive in the face
   858    of (rather peculiar) user-defined axioms. *)
   859 val harmless_consts =
   860   [@{const_name ord_class.less}, @{const_name ord_class.less_eq}]
   861 val bounteous_consts = [@{const_name bisim}]
   862 
   863 (* term -> bool *)
   864 fun is_harmless_axiom t =
   865   Term.add_consts t [] |> filter_out (is_built_in_const true)
   866   |> (forall (member (op =) harmless_consts o original_name o fst)
   867       orf exists (member (op =) bounteous_consts o fst))
   868 
   869 (* cdata -> sign -> term -> accumulator -> accumulator *)
   870 fun consider_nondefinitional_axiom cdata sn t =
   871   not (is_harmless_axiom t) ? consider_general_formula cdata sn t
   872 
   873 (* cdata -> term -> accumulator -> accumulator *)
   874 fun consider_definitional_axiom (cdata as {ext_ctxt as {thy, ...}, ...}) t =
   875   if not (is_constr_pattern_formula thy t) then
   876     consider_nondefinitional_axiom cdata Pos t
   877   else if is_harmless_axiom t then
   878     I
   879   else
   880     let
   881       (* term -> accumulator -> accumulator *)
   882       val do_term = consider_term cdata
   883       (* typ -> term -> accumulator -> accumulator *)
   884       fun do_all abs_T body_t accum =
   885         let val abs_C = fresh_ctype_for_type cdata abs_T in
   886           accum |>> push_bound abs_C |> do_formula body_t |>> pop_bound
   887         end
   888       (* term -> term -> accumulator -> accumulator *)
   889       and do_implies t1 t2 = do_term t1 #> snd #> do_formula t2
   890       and do_equals t1 t2 accum =
   891         let
   892           val (C1, accum) = do_term t1 accum
   893           val (C2, accum) = do_term t2 accum
   894         in accum ||> add_ctypes_equal C1 C2 end
   895       (* term -> accumulator -> accumulator *)
   896       and do_formula _ (_, UnsolvableCSet) = unsolvable_accum
   897         | do_formula t accum =
   898           case t of
   899             Const (@{const_name all}, _) $ Abs (_, T1, t1) => do_all T1 t1 accum
   900           | @{const Trueprop} $ t1 => do_formula t1 accum
   901           | Const (@{const_name "=="}, _) $ t1 $ t2 => do_equals t1 t2 accum
   902           | @{const "==>"} $ t1 $ t2 => do_implies t1 t2 accum
   903           | @{const Pure.conjunction} $ t1 $ t2 =>
   904             accum |> do_formula t1 |> do_formula t2
   905           | Const (@{const_name All}, _) $ Abs (_, T1, t1) => do_all T1 t1 accum
   906           | Const (@{const_name "op ="}, _) $ t1 $ t2 => do_equals t1 t2 accum
   907           | @{const "op &"} $ t1 $ t2 => accum |> do_formula t1 |> do_formula t2
   908           | @{const "op -->"} $ t1 $ t2 => do_implies t1 t2 accum
   909           | _ => raise TERM ("Nitpick_Mono.consider_definitional_axiom.\
   910                              \do_formula", [t])
   911     in do_formula t end
   912 
   913 (* Proof.context -> literal list -> term -> ctype -> string *)
   914 fun string_for_ctype_of_term ctxt lits t C =
   915   Syntax.string_of_term ctxt t ^ " : " ^
   916   string_for_ctype (instantiate_ctype lits C)
   917 
   918 (* theory -> literal list -> ctype_context -> unit *)
   919 fun print_ctype_context ctxt lits ({frees, consts, ...} : ctype_context) =
   920   map (fn (x, C) => string_for_ctype_of_term ctxt lits (Free x) C) frees @
   921   map (fn (x, (C, _)) => string_for_ctype_of_term ctxt lits (Const x) C) consts
   922   |> cat_lines |> print_g
   923 
   924 (* extended_context -> typ -> term list -> term list -> term -> bool *)
   925 fun formulas_monotonic (ext_ctxt as {ctxt, ...}) alpha_T def_ts nondef_ts
   926                        core_t =
   927   let
   928     val _ = print_g ("****** " ^ string_for_ctype CAlpha ^ " is " ^
   929                      Syntax.string_of_typ ctxt alpha_T)
   930     val cdata as {max_fresh, ...} = initial_cdata ext_ctxt alpha_T
   931     val (gamma, cset) =
   932       (initial_gamma, slack)
   933       |> fold (consider_definitional_axiom cdata) def_ts
   934       |> fold (consider_nondefinitional_axiom cdata Pos) nondef_ts
   935       |> consider_general_formula cdata Pos core_t
   936   in
   937     case solve (!max_fresh) cset of
   938       SOME lits => (print_ctype_context ctxt lits gamma; true)
   939     | _ => false
   940   end
   941   handle CTYPE (loc, Cs) => raise BAD (loc, commas (map string_for_ctype Cs))
   942 
   943 end;