(*  Title:      HOL/Tools/Predicate_Compile/code_prolog.ML

     Author:     Lukas Bulwahn, TU Muenchen

 Prototype of an code generator for logic programming languages (a.k.a. Prolog)

 *)

 signature CODE_PROLOG =

 sig

   datatype term = Var of string * typ | Cons of string | AppF of string * term list;

   datatype prem = Conj of prem list | NotRel of string * term list | Rel of string * term list | Eq of term * term | NotEq of term * term;

   type clause = ((string * term list) * prem);

   type logic_program = clause list;

   val generate : Proof.context -> string list -> logic_program

   val write_program : logic_program -> string

   val run : logic_program -> string -> string list -> unit

 end;

 structure Code_Prolog : CODE_PROLOG =

 struct

 (* general string functions *)

 val first_upper = implode o nth_map 0 Symbol.to_ascii_upper o explode;

 val first_lower = implode o nth_map 0 Symbol.to_ascii_lower o explode;

 (* internal program representation *)

 datatype term = Var of string * typ | Cons of string | AppF of string * term list;

 datatype prem = Conj of prem list | NotRel of string * term list | Rel of string * term list | Eq of term * term | NotEq of term * term;

 fun dest_Rel (Rel (c, ts)) = (c, ts)

 type clause = ((string * term list) * prem);

 type logic_program = clause list;

 (* translation from introduction rules to internal representation *)

 (* assuming no clashing *)

 fun translate_const c = Long_Name.base_name c

 fun translate_term ctxt t =

   case strip_comb t of

     (Free (v, T), []) => Var (v, T) 

   | (Const (c, _), []) => Cons (translate_const c)

   | (Const (c, _), args) => AppF (translate_const c, map (translate_term ctxt) args)

   | _ => error ("illegal term for translation: " ^ Syntax.string_of_term ctxt t)

 fun translate_literal ctxt t =

   case strip_comb t of

     (Const (@{const_name "op ="}, _), [l, r]) => Eq (pairself (translate_term ctxt) (l, r))

   | (Const (c, _), args) => Rel (translate_const c, map (translate_term ctxt) args)

   | _ => error ("illegal literal for translation: " ^ Syntax.string_of_term ctxt t)

 fun NegRel_of (Rel lit) = NotRel lit

   | NegRel_of (Eq eq) = NotEq eq

 fun translate_prem ctxt t =  

     case try HOLogic.dest_not t of

       SOME t => NegRel_of (translate_literal ctxt t)

     | NONE => translate_literal ctxt t

 fun translate_intros ctxt gr const =

   let

     val intros = Graph.get_node gr const

     val (intros', ctxt') = Variable.import_terms true (map prop_of intros) ctxt

     fun translate_intro intro =

       let

         val head = HOLogic.dest_Trueprop (Logic.strip_imp_concl intro)

         val prems = map HOLogic.dest_Trueprop (Logic.strip_imp_prems intro) 

         val prems' = Conj (map (translate_prem ctxt') prems)

         val clause = (dest_Rel (translate_literal ctxt' head), prems')

       in clause end

   in map translate_intro intros' end

 fun generate ctxt const =

   let 

      fun strong_conn_of gr keys =

       Graph.strong_conn (Graph.subgraph (member (op =) (Graph.all_succs gr keys)) gr)

     val gr = Predicate_Compile_Core.intros_graph_of ctxt

     val scc = strong_conn_of gr const

     val _ = tracing (commas (flat scc))

   in

     maps (translate_intros ctxt gr) (flat scc)

   end

 (* transform logic program *)

 (** ensure groundness of terms before negation **)

 fun add_vars (Var x) vs = insert (op =) x vs

   | add_vars (Cons c) vs = vs

   | add_vars (AppF (f, args)) vs = fold add_vars args vs

 fun string_of_typ (Type (s, Ts)) = Long_Name.base_name s

 fun mk_groundness_prems ts =

   let

     val vars = fold add_vars ts []

     fun mk_ground (v, T) =

       Rel ("ground_" ^ string_of_typ T, [Var (v, T)])

   in

     map mk_ground vars

   end

 fun ensure_groundness_prem (NotRel (c, ts)) = Conj (mk_groundness_prems ts @ [NotRel (c, ts)]) 

   | ensure_groundness_prem (NotEq (l, r)) = Conj (mk_groundness_prems [l, r] @ [NotEq (l, r)])

   | ensure_groundness_prem (Conj ps) = Conj (map ensure_groundness_prem ps)

   | ensure_groundness_prem p = p

 fun ensure_groundness_before_negation p =

   map (apsnd ensure_groundness_prem) p

 (* code printer *)

 fun write_term (Var (v, _)) = first_upper v

   | write_term (Cons c) = first_lower c

   | write_term (AppF (f, args)) = first_lower f ^ "(" ^ space_implode ", " (map write_term args) ^ ")" 

 fun write_rel (pred, args) =

   pred ^ "(" ^ space_implode ", " (map write_term args) ^ ")" 

 fun write_prem (Conj prems) = space_implode ", " (map write_prem prems)

   | write_prem (Rel p) = write_rel p  

   | write_prem (NotRel p) = "not(" ^ write_rel p ^ ")"

   | write_prem (Eq (l, r)) = write_term l ^ " = " ^ write_term r

   | write_prem (NotEq (l, r)) = write_term l ^ " \\= " ^ write_term r

 fun write_clause (head, prem) =

   write_rel head ^ (if prem = Conj [] then "." else " :- " ^ write_prem prem ^ ".")

 fun write_program p =

   cat_lines (map write_clause p) 

 fun query_first rel vnames =

   "eval :- once("  ^ rel ^ "(" ^ space_implode ", " vnames ^ ")),\n" ^

   "writef('" ^ implode (map (fn v => v ^ " = %w\\n") vnames) ^"', [" ^ space_implode ", " vnames ^ "]).\n"

 val prelude =

   "#!/usr/bin/swipl -q -t main -f\n\n" ^

   ":- style_check(-singleton).\n\n" ^

   "main :- catch(eval, E, (print_message(error, E), fail)), halt.\n" ^

   "main :- halt(1).\n"

 (* calling external interpreter and getting results *)

 fun run p query_rel vnames =

   let

     val cmd = Path.named_root

     val prog = prelude ^ query_first query_rel vnames ^ write_program p

     val prolog_file = File.tmp_path (Path.basic "prolog_file")

     val _ = File.write prolog_file prog

     val (solution, _) = bash_output ("/usr/bin/swipl -f " ^ File.shell_path prolog_file)

   in

     tracing ("Prolog returns result:\n" ^ solution)

   end

 end;