src/HOL/Tools/float_syntax.ML
 author wenzelm Sat, 13 Feb 2010 23:24:57 +0100 changeset 35123 e286d5df187a parent 35115 446c5063e4fd child 37744 3daaf23b9ab4 permissions -rw-r--r--
modernized structures;
```
(*  Author:     Tobias Nipkow, TU Muenchen

Concrete syntax for floats.
*)

signature FLOAT_SYNTAX =
sig
val setup: theory -> theory
end;

structure Float_Syntax: FLOAT_SYNTAX =
struct

(* parse translation *)

local

fun mk_number i =
let
fun mk 0 = Syntax.const @{const_syntax Int.Pls}
| mk ~1 = Syntax.const @{const_syntax Int.Min}
| mk i =
let val (q, r) = Integer.div_mod i 2
in HOLogic.mk_bit r \$ (mk q) end;
in Syntax.const @{const_syntax Int.number_of} \$ mk i end;

fun mk_frac str =
let
val {mant = i, exp = n} = Syntax.read_float str;
val exp = Syntax.const @{const_syntax Power.power};
val ten = mk_number 10;
val exp10 = if n = 1 then ten else exp \$ ten \$ mk_number n;
in Syntax.const @{const_syntax divide} \$ mk_number i \$ exp10 end;

in

fun float_tr (*"_Float"*) [t as Const (str, _)] = mk_frac str
| float_tr (*"_Float"*) ts = raise TERM ("float_tr", ts);

end;

(* theory setup *)

val setup =
Sign.add_trfuns ([], [(@{syntax_const "_Float"}, float_tr)], [], []);

end;
```