src/HOL/Tools/numeral_syntax.ML
author wenzelm
Tue Aug 13 12:16:14 2002 +0200 (2002-08-13)
changeset 13495 af27202d6d1c
parent 13491 ddf6ae639f21
child 14981 e73f8140af78
permissions -rw-r--r--
more robust printing of numerals;
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(*  Title:      HOL/Tools/numeral_syntax.ML
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    ID:         $Id$
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    Author:     Markus Wenzel, TU Muenchen
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    License:    GPL (GNU GENERAL PUBLIC LICENSE)
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Concrete syntax for generic numerals.  Assumes consts and syntax of
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theory HOL/Numeral.
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*)
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signature NUMERAL_SYNTAX =
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sig
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  val setup: (theory -> theory) list
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end;
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structure NumeralSyntax: NUMERAL_SYNTAX =
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struct
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(* bits *)
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fun dest_bit (Const ("False", _)) = 0
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  | dest_bit (Const ("True", _)) = 1
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  | dest_bit _ = raise Match;
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(* bit strings *)   (*we try to handle superfluous leading digits nicely*)
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fun prefix_len _ [] = 0
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  | prefix_len pred (x :: xs) =
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      if pred x then 1 + prefix_len pred xs else 0;
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fun bin_of (Const ("bin.Pls", _)) = []
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  | bin_of (Const ("bin.Min", _)) = [~1]
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  | bin_of (Const ("Bit", _) $ bs $ b) = dest_bit b :: bin_of bs
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  | bin_of _ = raise Match;
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val dest_bin = HOLogic.int_of o bin_of;
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fun dest_bin_str tm =
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  let
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    val rev_digs = bin_of tm;
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    val (sign, zs) =
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      (case rev rev_digs of
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        ~1 :: bs => ("-", prefix_len (equal 1) bs)
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      | bs => ("", prefix_len (equal 0) bs));
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    val i = HOLogic.int_of rev_digs;
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    val num = string_of_int (abs i);
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  in
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    if i = 0 orelse i = 1 then raise Match
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    else sign ^ implode (replicate zs "0") ^ num
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  end;
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(* translation of integer numeral tokens to and from bitstrings *)
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fun numeral_tr (*"_Numeral"*) [t as Const (str, _)] =
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      (Syntax.const "Numeral.number_of" $ HOLogic.mk_bin (Syntax.read_xnum str))
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  | numeral_tr (*"_Numeral"*) ts = raise TERM ("numeral_tr", ts);
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fun numeral_tr' show_sorts (*"number_of"*) (Type ("fun", [_, T])) (t :: ts) =
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      let val t' = Syntax.const "_Numeral" $ Syntax.free (dest_bin_str t) in
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        if not (! show_types) andalso can Term.dest_Type T then t'
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        else Syntax.const Syntax.constrainC $ t' $ Syntax.term_of_typ show_sorts T
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      end
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  | numeral_tr' _ (*"number_of"*) T (t :: ts) =
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      if T = dummyT then Syntax.const "_Numeral" $ Syntax.free (dest_bin_str t)
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      else raise Match
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  | numeral_tr' _ (*"number_of"*) _ _ = raise Match;
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(* theory setup *)
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val setup =
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 [Theory.hide_consts false ["Numeral.bin.Pls", "Numeral.bin.Min"],
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  Theory.add_trfuns ([], [("_Numeral", numeral_tr)], [], []),
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  Theory.add_trfunsT [("number_of", numeral_tr'), ("Numeral.number_of", numeral_tr')]];
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end;