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MathGroup Archive 2003

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Re: Options[] creation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg39235] Re: Options[] creation
  • From: "Allan Hayes" <hay at haystack.demon.co.uk>
  • Date: Wed, 5 Feb 2003 00:11:03 -0500 (EST)
  • References: <b1nq2h$o3o$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Kyriakos,

Here is are two ways (but adding message can often take longer than the
original programming - much depends how much you want  to do).  In general
we want to model built in function behaviour by returning univaluated when
something goes wrong.

(1)
    Options[f]:=
        {Diameter->1,Shape-> Circle};

    f[x_, opts___?OptionQ]:=
      Module[{shp, diam},
        {shp,diam}= {Shape,Diameter}/.
          Flatten[{opts}]/.Options[f];
           If[
              MatchQ[{shp,diam},
                {Circle,_?Positive}|{Ellipsis,{_?Positive,_?Positive}}],
              program[x,opts],
          Message[f::bdshpdiam]
      ]]

Define the message.

    f::bdshpdiam= "The values of the options Shape and Diameter
incompatible.";

TEST.

    f[aa]

        program[aa]

    f[aa, Diameter->{2,3}]

        f::bdshpdiam: The values of the options Shape and Diameter
incompatible.

(2)

Here is an example of a flexible trechnique that allows us to monitor the
evaluation process and act on what happens.

    middle[x___]:=With[{result=middle1[x]},result/;result=!=$Failed]

We now test all aspects of the input and on-going evaluation and act on what
we find.

    middle1[x___]:=
      Module[{tag},
        Catch[If[
             Length[{x}]===1,
            If[OddQ[Length[x]],Throw[x[[Ceiling[Length[x]/2]]],tag],
              Message[middle::nodd];Throw[$Failed, tag]],
            Message[middle::argx,middle, Length[{x}]];Throw[$Failed,tag]
            ],
          tag]
        ]

    middle::nodd =
        "The argument of middle is expected to be normal with an odd number
of elements";

TEST

    middle[{1,2}]

        middle::nodd: The argument of middle is expected to be normal with
an odd \
        number of elements

        middle[{1,2}]


    middle[1,2]

        middle::argx: middle called with 2 arguments; 1 argument is
expected.

        middle[1,2]

    middle[p[1,2,3]]

        2


--
Allan

---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565




"Kyriakos Chourdakis" <k.chourdakis at qmul.ac.uk> wrote in message
news:b1nq2h$o3o$1 at smc.vnet.net...
> Dear all,
>
> Suppose I create a function f[x_,opts___]
> with options
> Shape in {Circle,  Ellipsis} and Diameter in R+, DiameterLong in R+,
> DiameterShort in R+
> Say that the defaults are
> Options[x]={Shape->Circle, Diameter->1.}
>
> The option Diameter makes sence only when Shape->Circle, and
> The options DiameterShort/Long make sense only when Shape->Ellipsis
>
> Is there a quick way to tell Mathematica to warn if these conditions are
> not satisfied? I could write a series of boolean tests, but I was
wondering
> if there is a more elegant way.
>
> Best,
>
> Kyriakos
>
>
>
> _____+*"*+____+*"*+___+*"*+__+*"*+_
>
> Kyriakos Chourdakis
> Lecturer in Financial Economics
>
> URL: http://www.qmw.ac.uk/~te9001
> tel: (++44) (+20) 7882 5086
> Dept of Economics
> University of London, QM
> London E1 4NS
> U.K.
>




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