Re: Re: Boolean type-checking
- To: mathgroup at smc.vnet.net
- Subject: [mg41863] Re: [mg41811] Re: Boolean type-checking
- From: Murray Eisenberg <murray at math.umass.edu>
- Date: Sat, 7 Jun 2003 00:08:54 -0400 (EDT)
- Organization: Mathematics & Statistics, Univ. of Mass./Amherst
- References: <bbnal0$2d4$1@smc.vnet.net> <200306061350.JAA13014@smc.vnet.net>
- Reply-to: murray at math.umass.edu
- Sender: owner-wri-mathgroup at wolfram.com
I want one behavior when the variable takes value True; another when
that variable takes value False; and an unevaluated expression returned
when the variable takes any other value (as by improper usage of the
function).
I do NOT want one behavior when the variable takes value True and an
alternative in every other case!
And I still raise the question as to why Mathematica does not have a
built-in object for {True, False}.
Jens-Peer Kuska wrote:
> Hi,
>
> hmm, and TrueQ[] does what ?
>
> TrueQ[expr] yields True if expr is True, and yields False otherwise.
>
> why do you want to to know if expr is False if you can check
> that it is true ?
>
> Regards
> jens
>
> Murray Eisenberg wrote:
>
>>When type checking the argument to a function, it's often easy to use a
>>built-in object in a pattern, e.g.:
>>
>> f[n_Integer] := n + 1
>>
>> g[x_?Positive] := Sqrt[x]
>>
>>But what about type-checking that an argument is Boolean, i.e., True or
>>False? Of course it's easy enough to define a function to do this:
>>
>> tfQ[sym_] := MemberQ[{True, False}, sym]
>> (* or: tfQ[sym_] := Element[sym, Booleans] *)
>>
>> h[y_, flag_?tfQ] := ....
>>
>>But is there no NAMED, single built-in object that does what the
>>above-defined tfQ does?
>>
>>If I am correct that there is not, this may result from what seems to be
>>a fundamental language design decision, namely, that True and False are
>>just symbols -- they do have head Symbol -- rather than being of a
>>special type having, say head Boolean. Why was that design decision made?
>>
>>--
>>Reply to "REPLY TO" address and NOT to the "FROM" address!!
>>Otherwise I will never see your reply!!!!!!!!!!!!!!!!!!!!!!
>>
>>Murray Eisenberg murray at math.umass.edu
>>Mathematics & Statistics Dept.
>>Lederle Graduate Research Tower phone 413 549-1020 (H)
>>University of Massachusetts 413 545-2859 (W)
>>710 North Pleasant Street fax 413 545-1801
>>Amherst, MA 01003-9305
>
>
>
--
Reply to "REPLY TO" address and NOT to the "FROM" address!!
Otherwise I will never see your reply!!!!!!!!!!!!!!!!!!!!!!
Murray Eisenberg murray at math.umass.edu
Mathematics & Statistics Dept.
Lederle Graduate Research Tower phone 413 549-1020 (H)
University of Massachusetts 413 545-2859 (W)
710 North Pleasant Street fax 413 545-1801
Amherst, MA 01003-9305
- References:
- Re: Boolean type-checking
- From: Jens-Peer Kuska <kuska@informatik.uni-leipzig.de>
- Re: Boolean type-checking