(*  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;