Skip to main content

core language - Is anonymous pure function a scoping construct?



In recent thread was raised the question: why anonymous pure functions Function[body] (or body &) do not rename symbols in nested scoping constructs while pure functions with named parameters Function[{vars}, body] do rename them as seen from the following example:


lhs_ :> # &@arg
Function[rhs, lhs_ :> rhs]@arg


lhs_ :> arg

lhs$_ :> arg

(in the second case lhs is renamed to lhs$).



The provided explanation (first given in the comment) states that pure function with no named arguments isn't a scoping construct, hence localization of variables in the nested scope isn't performed. This looks as kind of obvious since there is no need to localize variables inside of a construct which doesn't use variables itself (anonymous pure functions use only Slot).


But when trying to find where it is stated in the official Documentation, I was confused: the modern Documentation seems to state the opposite (although all the linked examples are only about the form Function[{vars}, body]), emphasis is mine:



Function constructs can be nested in any way. Each is treated as a scoping construct, with named inner variables being renamed if necessary. »



At the same time Leonid Shifrin notes in his book "Mathematica programming: an advanced introduction" (emphasis is mine):



It is important to note that there is no fundamental difference between functions defined with the # - & notation and functions defined with the Function command, in the sense that both definitions produce pure functions. There are however several technical differences that need to be mentioned.


The first one is that the Function[{vars},body] is a scoping construct, similar to Module, Block, With etc.




what implies that only the form Function[{vars},body] is a scoping construct, not the form defined with the # - & notation.


Let us make the things clear: is the form Function[body] (and equivalent forms body & and Function[Null, body]) a scoping construct or not? I ask both for authoritative references and for rational analysis of the situation.




Comments

Post a Comment

Popular posts from this blog

functions - Get leading series expansion term?

Given a function f[x] , I would like to have a function leadingSeries that returns just the leading term in the series around x=0 . For example: leadingSeries[(1/x + 2)/(4 + 1/x^2 + x)] x and leadingSeries[(1/x + 2 + (1 - 1/x^3)/4)/(4 + x)] -(1/(16 x^3)) Is there such a function in Mathematica? Or maybe one can implement it efficiently? EDIT I finally went with the following implementation, based on Carl Woll 's answer: lds[ex_,x_]:=( (ex/.x->(x+O[x]^2))/.SeriesData[U_,Z_,L_List,Mi_,Ma_,De_]:>SeriesData[U,Z,{L[[1]]},Mi,Mi+1,De]//Quiet//Normal) The advantage is, that this one also properly works with functions whose leading term is a constant: lds[Exp[x],x] 1 Answer Update 1 Updated to eliminate SeriesData and to not return additional terms Perhaps you could use: leadingSeries[expr_, x_] := Normal[expr /. x->(x+O[x]^2) /. a_List :> Take[a, 1]] Then for your examples: leadingSeries[(1/x + 2)/(4 + 1/x^2 + x), x] leadingSeries[Exp[x], x] leadingSeries[(1/x + 2 + (1 - 1/x...
Post a Comment
Read more

How to thread a list

I have data in format data = {{a1, a2}, {b1, b2}, {c1, c2}, {d1, d2}} Tableform: I want to thread it to : tdata = {{{a1, b1}, {a2, b2}}, {{a1, c1}, {a2, c2}}, {{a1, d1}, {a2, d2}}} Tableform: And I would like to do better then pseudofunction[n_] := Transpose[{data2[[1]], data2[[n]]}]; SetAttributes[pseudofunction, Listable]; Range[2, 4] // pseudofunction Here is my benchmark data, where data3 is normal sample of real data. data3 = Drop[ExcelWorkBook[[Column1 ;; Column4]], None, 1]; data2 = {a #, b #, c #, d #} & /@ Range[1, 10^5]; data = RandomReal[{0, 1}, {10^6, 4}]; Here is my benchmark code kptnw[list_] := Transpose[{Table[First@#, {Length@# - 1}], Rest@#}, {3, 1, 2}] &@list kptnw2[list_] := Transpose[{ConstantArray[First@#, Length@# - 1], Rest@#}, {3, 1, 2}] &@list OleksandrR[list_] := Flatten[Outer[List, List@First[list], Rest[list], 1], {{2}, {1, 4}}] paradox2[list_] := Partition[Riffle[list[[1]], #], 2] & /@ Drop[list, 1] RM[list_] := FoldList[Transpose[{First@li...
Post a Comment
Read more

front end - keyboard shortcut to invoke Insert new matrix

I frequently need to type in some matrices, and the menu command Insert > Table/Matrix > New... allows matrices with lines drawn between columns and rows, which is very helpful. I would like to make a keyboard shortcut for it, but cannot find the relevant frontend token command (4209405) for it. Since the FullForm[] and InputForm[] of matrices with lines drawn between rows and columns is the same as those without lines, it's hard to do this via 3rd party system-wide text expanders (e.g. autohotkey or atext on mac). How does one assign a keyboard shortcut for the menu item Insert > Table/Matrix > New... , preferably using only mathematica? Thanks! Answer In the MenuSetup.tr (for linux located in the $InstallationDirectory/SystemFiles/FrontEnd/TextResources/X/ directory), I changed the line MenuItem["&New...", "CreateGridBoxDialog"] to read MenuItem["&New...", "CreateGridBoxDialog", MenuKey["m", Modifiers-...
Post a Comment
Read more