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MathGroup Archive 2005

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Re: 'Raw Expressions'

  • To: mathgroup at
  • Subject: [mg61654] Re: 'Raw Expressions'
  • From: "Jens-Peer Kuska" <kuska at>
  • Date: Mon, 24 Oct 2005 21:07:12 -0400 (EDT)
  • Organization: Uni Leipzig
  • References: <djht17$sjt$>
  • Sender: owner-wri-mathgroup at


what man N[] do ??


"Matt" <anonmous69 at> schrieb im 
Newsbeitrag news:djht17$sjt$1 at
| Hello,
|     Given this as input:
| someArray = Array[r, {2, 2}, {2, 4}];
| Level[someArray, {-1}]
| which results in the following output:
| {2, 4, 2, 5, 3, 4, 3, 5}
| and the fact that a level specification of -1 is 
defined thusly:
| "Level -1 contains all symbols and other objects 
that have no
| subparts",
| one would naively expect that this:
| Apply[HeadNew, someArray, {-1}]
| would change all the integers in someArray to 
have new heads of
| NewHead.  However, on page 711 of Michael 
Trott's Programming
| Guidebook, he states "The head of raw 
expressions does not get changed
| by Apply."  I assume that by 'raw expression' he 
means fundamental
| types such as Integers, Reals, Strings, etc. 
This makes sense to me,
| because it would be nonsensical to change the 
head of an integer to be
| String or vice versa.  However, a question did 
occur to me in the
| hypothetical.  Let's say that a function had 
been defined that had a
| constraint upon a certain input, in that the 
input needed to be of
| Integer type, but for some reason, I wanted to 
deal with the input
| internally as a type of Real.  How would I do 
| Thanks,
| Matt

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