src/HOL/Tools/numeral_syntax.ML
author wenzelm
Sun Dec 10 22:27:06 2006 +0100 (2006-12-10)
changeset 21763 12a2773e3608
parent 20094 99f27df2b6d0
child 21780 ec264b9daf94
permissions -rw-r--r--
tuned comments;
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(*  Title:      HOL/Tools/numeral_syntax.ML
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    ID:         $Id$
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    Authors:    Markus Wenzel, TU Muenchen
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Concrete syntax for generic numerals.
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*)
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signature NUMERAL_SYNTAX =
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sig
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  val setup: theory -> theory
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end;
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structure NumeralSyntax: NUMERAL_SYNTAX =
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struct
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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 dest_bin_str tm =
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  let
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    val rev_digs = HOLogic.bin_of tm handle TERM _ => raise Match
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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 = IntInf.toString (IntInf.abs i);
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  in
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    if i = IntInf.fromInt 0 orelse i = IntInf.fromInt 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_binum (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.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;