Re: RE: Should Pure Functions Require &

*To*: mathgroup at smc.vnet.net*Subject*: [mg29777] Re: [mg29775] RE: Should Pure Functions Require &*From*: Andrzej Kozlowski <andrzej at tuins.ac.jp>*Date*: Sun, 8 Jul 2001 20:35:53 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

I think in order to do what you would like you would have to add to Mathematica quite a lot of rules for deciding where to insert & in more complicated cases, e.g. Select[Range[100],Function[x,x>#]]&/@Range[10]; The point is that even if Mathematica was able to correctly decide where to insert the & and even if Mathematica programmers could remember all the rules which you stated in your message (and which, by the way, I can't understand because I do not understand what you mean when you write >where test has " " and so on), implementing your idea would encourage people to write even more unreadable code than they do at present. I find the idea of trying to understand such code quite dreadful. Thus I would strongly oppose your idea on the grounds of wanting to preserve my sanity. By the way, I there is a reasonable use for # without & ( well, sort of). Here is a somewhat artificial example. This makes a list of expressions {#,#^2,...} which can be manipulated just as any algebraic expressions. l = Table[#^i, {i, 1, 100}]; This converts them to pure functions: In[2]:= v=Function/@l; For example: In[3]:= v[[15]][3] Out[3]= 14348907 -- Andrzej Kozlowski Toyama International University JAPAN http://platon.c.u-tokyo.ac.jp/andrzej/ http://sigma.tuins.ac.jp/~andrzej/ on 01.7.8 2:00 PM, Ersek, Ted R at ErsekTR at navair.navy.mil wrote: > Earlier I wrote: > -------------------- >> I stated wondering if all would work well if pure functions didn't require >> & at the end. I am thinking it would be great if a future version of >> Mathematica would make the use of & optional. >> >> So for example we could use >> Select[data, #!=0] >> instead of >> Select[data, #!=0&] >> >> >> and we could use >> #^2 /@expr >> instead of >> #^2& /@expr >> >> I would want to have pure functions ending with & optional rather than >> prohibited for backward compatibility. Wouldn't life be better if we >> didn't have to use &. Is there a reason why my suggestion would not work? >> > ----------------- > Orestis Vantzos, > asked whether Select[data, #!=0] > should do what Select[data, #!=0&] does now, > or what Select[data, #!0]& does now. > > In that case one clearly wants Select[data, #!=0&] > since the other case is a pure function that always returns an empty > list. > > ---------------- > The way I would like to see it the kernel would put an & at a > suitable place in the following situations. > 1 A head has one or more #, #n, ##, or ##n but no &. > 2 Use of expr/;test, _?test, __?test, ___?test where test has > " ". > 3 The right side of Set, or SetDelayed has " ". > 4 The second argument of Select, MatrixQ, VectorQ has " ". > 5 An argument of a functional programming construct includes #, #n, > ##, or ##n but no & and a function is expected in this argument. > > Examples of 5 > > In[1]:= g = {##+1, ##+2}; > Through[ g[{x,y,z}] ] > > This would return the same thing as if we had g = {##+1&, ##+2& } > since Through expects an argument of the form p[func1, func2][x] > > > In[2]:= g= {##+1, ##+2}; > Apply[ g, {x,y,z} ] > > This would return the same thing as if we had g= {##+1, ##+2}& > since Apply expects the first argument to be a function. > > > In[3]:= Clear[g]; Apply[g, {x,y,z}] > > Out[3]= g[x,y,z] > > In this case (g) has no #, #n, ##, ##n so an (&) would not be > assumed. > > > I haven't found a case where the "missing" (&) could go "here" or > "there" and both decisions would be useful. Also I am not aware of a use for > #, #n, ##, ##n without an (&). > > ------------------ >> Regards, >> Ted Ersek >> Download Mathematica tips, tricks from >> http://www.verbeia.com/mathematica/tips/Tricks.html >> > >

**Re: Should Pure Functions Require &**

**boolean operations for polygons**

**Re: Should Pure Functions Require &**

**Re: RE: Should Pure Functions Require &**