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MathGroup Archive 2004

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RE: Re: Length of actual parameters in a function call.

  • To: mathgroup at smc.vnet.net
  • Subject: [mg47193] RE: [mg47124] Re: Length of actual parameters in a function call.
  • From: "E. Martin-Serrano \(Houston - USA\)" <eMartinSerrano at houston.rr.com>
  • Date: Mon, 29 Mar 2004 04:22:39 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Many Thanks.


-----Original Message-----
From: Paul Abbott [mailto:paul at physics.uwa.edu.au] 
To: mathgroup at smc.vnet.net
Subject: [mg47193] Re: [mg47124] Re: Length of actual parameters in a function call.

At 1:30 PM +0000 26/3/04, Andrzej Kozlowski wrote:

>On 26 Mar 2004, at 08:56, Paul Abbott wrote:
>
>>In article <c3udpe$9om$1 at smc.vnet.net>,
>>  "E. Martin-Serrano" <eMartinSerrano at houston.rr.com> wrote:
>>
>>>A few weeks ago, reviewing some tutorials on pattern matching and error
>>>handling, I came across an undocumented function to monitor the number of
>>>parameters submitted to a function in a call; but somehow I lost its
track
>>>later. I guess that it must be something well-known by our specialists.
Any
>>>help about where to locate it?
>>>
>>>The undocumented feature helps in tracking situations as when we define
>>>"MyFunction[a_,b_,c_]:= something" and then it is called as
"myFunction[a]"
>>>leaving the function unevaluated.
>>
>>   MyFunction[a_, b_, c_] := something
>>
>>   MyFunction[args___] := Null /; Length[{args}] != 3 &&
>>     Message[MyFunction::argx, MyFunction, Length[{args}]]
>>
>>   MyFunction[a]
>>
>>Cheers,
>>Paul
>>
>>--
>>Paul Abbott                                   Phone: +61 8 9380 2734
>>School of Physics, M013                         Fax: +61 8 9380 1014
>>The University of Western Australia      (CRICOS Provider No 00126G)
>>35 Stirling Highway
>>Crawley WA 6009                      mailto:paul at physics.uwa.edu.au
>>AUSTRALIA                            http://physics.uwa.edu.au/~paul
>>
>>
>
>This does not seem to produce the correct message; I think you need 
>something like:
>
>  MyFunction[a_, b_, c_] := something
>
>MyFunction::"argx" = "MyFunction called with `1` arguments, 3 arguments are
\
>expected."
>
>MyFunction[args___] := Null /; Length[{args}] != 3 &&
>     Message[MyFunction::argx, Length[{args}]]
>
>
>MyFunction[a]

Actually, I wanted to use the appropriate built-in message. Having 
another look at Messages.m in 
SystemFiles`Kernel`TextResources`English`, argrx, is the one to use:

   Clear[MyFunction]

   MyFunction[a_, b_, c_] := something

   MyFunction[args___] := Null /; Length[{args}] != 3 &&
     Message[MyFunction::argrx, MyFunction, Length[{args}],3]

   MyFunction[a]

Cheers,
Paul



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