Re: Evaluate[] not needed in With[]

*To*: mathgroup at smc.vnet.net*Subject*: [mg63128] Re: Evaluate[] not needed in With[]*From*: "Steven T. Hatton" <hattons at globalsymmetry.com>*Date*: Thu, 15 Dec 2005 03:06:36 -0500 (EST)*References*: <dnbnav$5ti$1@smc.vnet.net> <dnbqf0$7af$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Jens-Peer Kuska wrote: > Hi, > > With[] does a (clever) ReplaceAll[] of the constants > you give, in its body before the body is evaluated. > This means that the argument of ParametricPlot[] in your > example is replaced by the value of hlines .. > and so you don't need a Evaluate[]. I believe my confusion came from not really understanding what Evaluate[] does in this context. Basically, it takes and expression that evaluates to a "function", and forces the expression to produce the function based on the current environment, rather than waiting till the function itself would be evaluated. It's kind of like producing a (mathematical) function of a single variable from a function of several variable by replacing all but one of the variables with constants. Given an expression 'expr' that evaluates to a function, when expr appears as the value of a Set expression it must be evaluated to the function. There are probably better words for this, but that's the general idea. -- The Mathematica Wiki: http://www.mathematica-users.org/ Math for Comp Sci http://www.ifi.unizh.ch/math/bmwcs/master.html Math for the WWW: http://www.w3.org/Math/