Re: pure function

*To*: mathgroup at smc.vnet.net*Subject*: [mg113716] Re: pure function*From*: Stephan <stschiff80 at googlemail.com>*Date*: Mon, 8 Nov 2010 05:40:39 -0500 (EST)

Ah, I forgot a follow up: What if I don't want to use a constant like in the example I stated? What if I want to compute the local value of a in the module and return the computed value instead of the symbol? I am kind of looking for a general way to evaluate a part of an expression within the delayed evaluation of the function body. Thanks, Stephan Am 08.11.2010 um 09:20 schrieb Leonid Shifrin: > Stephan, > > Yes, sure, use With instead of Module: > > In[2]:== getFunc:==With[{a==2},Function[{x},a*x]] > > In[3]:== f==getFunc > > Out[3]== Function[{x$},2 x$] > > So, by using Module, you can create a closure whose state (variable <a> > in this case) comes from surrounding context but can be modified by it > at a later time. Using With gets you a textual substitution of a value that > a given expression had, at the moment when With was invoked. > > You can also accomplish your goal somewhat differently, by redefining your getFunc: > > In[4]:== > Clear[getFunc]; > getFunc[y_] :== Function[{x}, y*x] > > In[6]:== getFunc[2] > > Out[6]== Function[{x$}, 2 x$] > > The semantics of parameter-passing in Mathematica is somewhat similar to With: > parameters are textually substituted to the body before the body starts to evaluate. > There are a few subtle differences (related to name collision resolution in nested > scoping constructs), but they do not show up in this particular case. > > Regards, > Leonid > > > On Mon, Nov 8, 2010 at 11:37 AM, Stephan <stschiff80 at googlemail.com> wrote: > Hi, > > I have a function that returns a pure function: > > In[1]:== getFunc :== Module[{a==2}, Function[{x}, a * x]] > > In[2]:== f == getFunc > > Out[2]== Function[{x$}, a$57 x$] > > > Is there any way, to have the body of the returned function contain the a= ctual _value_ of the local variable a, instead of the _symbol_ ? > > So I would like the returned function to be written as > > Function[{x$}, 2 x$] > > The reason is, that I would like to have a quick way to actually see the = value instead of digging out the local variable a$57... > > Thanks, > > Stephan > >