(*  Title:      Tools/value.ML

    Author:     Florian Haftmann, TU Muenchen

Generic value command for arbitrary evaluators.

*)

signature VALUE =

sig

  val value: Proof.context -> term -> term

  val value_select: string -> Proof.context -> term -> term

  val value_cmd: string option -> string list -> string -> Toplevel.state -> unit

  val add_evaluator: string * (Proof.context -> term -> term) -> theory -> theory

  val setup : theory -> theory

end;

structure Value : VALUE =

struct

structure Evaluator = Theory_Data

(

  type T = (string * (Proof.context -> term -> term)) list;

  val empty = [];

  val extend = I;

  fun merge data : T = AList.merge (op =) (K true) data;

)

val add_evaluator = Evaluator.map o AList.update (op =);

fun value_select name ctxt =

  case AList.lookup (op =) (Evaluator.get (Proof_Context.theory_of ctxt)) name

   of NONE => error ("No such evaluator: " ^ name)

    | SOME f => f ctxt;

fun value ctxt t = let val evaluators = Evaluator.get (Proof_Context.theory_of ctxt)

  in if null evaluators then error "No evaluators"

  else let val (evaluators, (_, evaluator)) = split_last evaluators

    in case get_first (fn (_, f) => try (f ctxt) t) evaluators

     of SOME t' => t'

      | NONE => evaluator ctxt t

  end end;

fun value_maybe_select some_name =

  case some_name

    of NONE => value

     | SOME name => value_select name;

fun value_cmd some_name modes raw_t state =

  let

    val ctxt = Toplevel.context_of state;

    val t = Syntax.read_term ctxt raw_t;

    val t' = value_maybe_select some_name ctxt t;

    val ty' = Term.type_of t';

    val ctxt' = Variable.auto_fixes t' ctxt;

    val p = Print_Mode.with_modes modes (fn () =>

      Pretty.block [Pretty.quote (Syntax.pretty_term ctxt' t'), Pretty.fbrk,

        Pretty.str "::", Pretty.brk 1, Pretty.quote (Syntax.pretty_typ ctxt' ty')]) ();

  in Pretty.writeln p end;

val opt_modes =

  Scan.optional (@{keyword "("} |-- Parse.!!! (Scan.repeat1 Parse.xname --| @{keyword ")"})) [];

val opt_evaluator =

  Scan.option (@{keyword "["} |-- Parse.xname --| @{keyword "]"})

val _ =

  Outer_Syntax.improper_command "value" "evaluate and print term" Keyword.diag

    (opt_evaluator -- opt_modes -- Parse.term

      >> (fn ((some_name, modes), t) => Toplevel.no_timing o Toplevel.keep

          (value_cmd some_name modes t)));

val antiq_setup =

  Thy_Output.antiquotation @{binding value}

    (Scan.lift opt_evaluator -- Term_Style.parse -- Args.term)

    (fn {source, context, ...} => fn ((some_name, style), t) => Thy_Output.output context

      (Thy_Output.maybe_pretty_source Thy_Output.pretty_term context source

        [style (value_maybe_select some_name context t)]));

val setup = antiq_setup;

end;