Skip to main content

parsing - FullForm with context for each symbol?


FullForm strips the context for any symbol that can be found on the Append[$ContextPath, $Context]: FullForm[System`List] is displayed List, but I would like to get System`List for debugging and learning purposes.


I tried $ContextPath = {} but then the whole front-end stops working [1].


Is there another way besides


Hold[...] /. x_Symbol :> (Context@x <> SymbolName@Unevaluated@x)

Is there any case where this would not work?




[1] I find it strange that the internal code of the FrontEnd relies on the "usability features" $Context and $ContextPath. Why doesn't it use the full symbol names for any code it uses (or produces)? IMO $ContextPath = {} should hurt you (having to type the full name of any symbols not in $Context), but not the system. If it really needs System` to operate properly, it should not allow setting $ContextPath = {} just like it is not allowed to set $Context to something invalid.


[2] Note that Context has HoldFirst while SymbolName doesn't, hence the Unevaluated.



Answer





  1. To not mess with $ContextPath you can Block it just for that evaluation. e.g. Block[{$ContextPath = {}}, ...].


    But we don't want to do that for the evaluation, input for FullForm should be evaluated freely and only the result should be returned with full symbols' names.


    To achieve that you should know:





  2. $ContextPath and $Context affect the typesetting. MakeBoxes will strip those contexts from an evaluated FullForm.




So, to deal with 2 we have to perform MakeBoxes on our rules (local contexts values) and order that to not be touched by MakeBoxes anymore (RawBoxes):


Block[{$ContextPath = {}, $Context = "other`"}
   ,
   RawBoxes @ ToBoxes @ FullForm @ {x, 1}
] 



System`List[Global`x,1]

It is very convenient when we want to "toggle a visibility" of specific contexts:


Block[{$ContextPath = {"System`"}, ...


 List[Global`x,1]

Comments

Post a Comment

Popular posts from this blog

mathematical optimization - Minimizing using indices, error: Part::pkspec1: The expression cannot be used as a part specification

I want to use Minimize where the variables to minimize are indices pointing into an array. Here a MWE that hopefully shows what my problem is. vars = u@# & /@ Range[3]; cons = Flatten@ { Table[(u[j] != #) & /@ vars[[j + 1 ;; -1]], {j, 1, 3 - 1}], 1 vec1 = {1, 2, 3}; vec2 = {1, 2, 3}; Minimize[{Total@((vec1[[#]] - vec2[[u[#]]])^2 & /@ Range[1, 3]), cons}, vars, Integers] The error I get: Part::pkspec1: The expression u[1] cannot be used as a part specification. >> Answer Ok, it seems that one can get around Mathematica trying to evaluate vec2[[u[1]]] too early by using the function Indexed[vec2,u[1]] . The working MWE would then look like the following: vars = u@# & /@ Range[3]; cons = Flatten@{ Table[(u[j] != #) & /@ vars[[j + 1 ;; -1]], {j, 1, 3 - 1}], 1 vec1 = {1, 2, 3}; vec2 = {1, 2, 3}; NMinimize[ {Total@((vec1[[#]] - Indexed[vec2, u[#]])^2 & /@ R...
Post a Comment
Read more

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

What is and isn't a valid variable specification for Manipulate?

I have an expression whose terms have arguments (representing subscripts), like this: myExpr = A[0] + V[1,T] I would like to put it inside a Manipulate to see its value as I move around the parameters. (The goal is eventually to plot it wrt one of the variables inside.) However, Mathematica complains when I set V[1,T] as a manipulated variable: Manipulate[Evaluate[myExpr], {A[0], 0, 1}, {V[1, T], 0, 1}] (*Manipulate::vsform: Manipulate argument {V[1,T],0,1} does not have the correct form for a variable specification. >> *) As a workaround, if I get rid of the symbol T inside the argument, it works fine: Manipulate[ Evaluate[myExpr /. T -> 15], {A[0], 0, 1}, {V[1, 15], 0, 1}] Why this behavior? Can anyone point me to the documentation that says what counts as a valid variable? And is there a way to get Manpiulate to accept an expression with a symbolic argument as a variable? Investigations I've done so far: I tried using variableQ from this answer , but it says V[1...
Post a Comment
Read more