Re: Membership in "set" of characters

[mab@wdl39.wdl.loral.com (Mark A Biggar)]

In article <J6QBBP3L@math.fu-berlin.de> dww@math.fu-berlin.de (Debora Weber-Wulff) writes:
>with text_io; use text_io;
>procedure muell3 is
>type affirmatives is ('y', 'Y', 'j', 'J', 'o', 'O');
>  ch : CHARACTER;
>  okay : Boolean;
>begin
>  get (ch);
>  -- The next statement gets flagged with
>  -- type clash in membership test [LRM 4.5.2/10]
>  okay := ch IN affirmatives;
>end muell3;

The error message from the compiler is correct type CHARACTER clashes with
type affirmatives.  The only way to do what you want is to cheat using 'value
and 'image like so

okay := affirmatives'VALUE(CHARACTER'IMAGE(ch)) in affirmatives;

and even this may not work because not all values of type CHARACTER have
a 'IMAGE.

A much better method of doing this in Ada is to use a table lookup like so:

type CHAR_SET is array(CHARACTER) of BOOLEAN;
AFFIRMATIVES : CHAR_SET := CHAR_SET'('y'|'Y'|'j'|'J'|'o'|'O' => TRUE,
				others => FALSE);

then use the following for the test

okay := AFFIRMATIVES(ch);

--
Mark Biggar
mab@wdl1.wdl.loral.com