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(*
Title: Standard Basis Library: Bool Structure
Author: David Matthews
Copyright David Matthews 1999, 2005, 2016
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License version 2.1 as published by the Free Software Foundation.
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 Bool (* Defined in Initialise. Contains bool datatype and "not". *)
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 _ 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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