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MathGroup Archive 2005

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Re: 2.9.2 How Input and Output Work

  • To: mathgroup at smc.vnet.net
  • Subject: [mg61866] Re: 2.9.2 How Input and Output Work
  • From: Bill Rowe <readnewsciv at earthlink.net>
  • Date: Wed, 2 Nov 2005 04:09:37 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

On 11/1/05 at 12:39 AM, hattons at globalsymmetry.com (Steven T.
Hatton) wrote:

>2.9.2 How Input and Output Work of the online help states that:

>"When you type something like x^2 what Mathematica at first sees is
>just the string of characters x, ^, 2. But with the usual way that
>Mathematica is set up, it immediately knows to convert this string
>of characters into the expression Power[x, 2]."

>What does "immediately" mean in this context?  As soon as I press
>the '2' key?  When I evaluate the cell?  If it is the former, then
>why do I see "Cell[BoxData[SuperscriptBox["x", "2"]], "Input"]"
>when I view the expression?

Immediately has to mean when you evaluate the cell. If Mathematica converted x^2 into Power[x,2] when you press the '2' key, how would it be possible to see x^24 as Power[x, 24] and not Power[x, 2]? 

Clearly, Mathematica has to wait until you have completely entered the expression. And since expressions have arbitrary length, there is no feasible way for Mathematica to know when the expression is complete until you ask Mathematica to evaluate it by evaluating the cell.
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