Re: Boolean type-checking
- To: mathgroup at smc.vnet.net
- Subject: [mg41811] Re: Boolean type-checking
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Fri, 6 Jun 2003 09:50:41 -0400 (EDT)
- Organization: Universitaet Leipzig
- References: <bbnal0$2d4$1@smc.vnet.net>
- Reply-to: kuska at informatik.uni-leipzig.de
- Sender: owner-wri-mathgroup at wolfram.com
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
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