(* Title: HOL/Tools/float_syntax.ML
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 1 = Syntax.const @{const_syntax Num.One}
| mk i =
let val (q, r) = Integer.div_mod i 2
in HOLogic.mk_bit r $ (mk q) end;
in
if i = 0 then Syntax.const @{const_syntax Groups.zero}
else if i > 0 then Syntax.const @{const_syntax Num.numeral} $ mk i
else Syntax.const @{const_syntax Num.neg_numeral} $ mk (~i)
end;
fun mk_frac str =
let
val {mant = i, exp = n} = Lexicon.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 [(c as Const (@{syntax_const "_constrain"}, _)) $ t $ u] = c $ float_tr [t] $ u
| float_tr [t as Const (str, _)] = mk_frac str
| float_tr ts = raise TERM ("float_tr", ts);
end;
(* theory setup *)
val setup =
Sign.add_trfuns ([], [(@{syntax_const "_Float"}, float_tr)], [], []);
end;