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(*
Title: Standard Basis Library: Bool Structure
Author: David Matthews
Copyright David Matthews 1999, 2005
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*)
(* G&R status: Minor change to signature. Done. *)
signature BOOL =
sig
datatype bool = datatype bool
val not : bool -> bool
val fromString : string -> bool option
val scan : (char, 'a) StringCvt.reader -> (bool, 'a) StringCvt.reader
val toString : bool -> string
end;
structure Bool : BOOL =
struct
open RuntimeCalls; (* for POLY_SYS and EXC numbers *)
datatype bool = datatype bool
val not: bool -> bool = RunCall.run_call1 POLY_SYS_not_bool;
local
val explode_true = Text.String.explode "true"
and explode_false = Text.String.explode "false"
in
fun scan (getc: (char, 'a) StringCvt.reader) (str: 'a) : (bool * 'a) option =
let
(* Skip leading white space. *)
val strm = StringCvt.skipWS getc str
(* Test for a match between a reader and a list of lower case chars. *)
fun matchNC getc strm [] = (strm, true )(* Reached end of list - succeeded *)
| matchNC getc strm (ch::rest) =
case getc strm of
NONE => (strm, false) (* Couldn't read it - fail. *)
| SOME(ch', strm') =>
if ch = Char.toLower ch' (* N.B. ch is already lower case. *)
then matchNC getc strm' rest
else (strm', false)
in
(* If it matches "true" or "false" we have a valid match,
otherwise return NONE. *)
case matchNC getc strm explode_true of
(strm', true) => SOME(true, strm')
| _ =>
(
case matchNC getc strm explode_false of
(strm', true) => SOME(false, strm')
| _ => NONE
)
end
end
(* Convert from a string. *)
(* TODO: More efficient conversion? *)
val fromString = StringCvt.scanString scan
(* Convert to a string. *)
fun toString true = "true"
| toString false = "false"
end;
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