Questions tagged [scoping]

Questions on Mathematica's scoping constructs (Block, Module, With, etc.)

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235
votes
8answers
15k views

What are the use cases for different scoping constructs?

Mathematica includes three functions that I know of which can be used to effectively (if not actually) define a variable and give it a value within a local scope: ...
49
votes
5answers
2k views

Enforcing correct variable bindings and avoiding renamings for conflicting variables in nested scoping constructs

Using global variables the following turns an "expression" into a Function: expr = 2 x; Function[x, Evaluate[expr]] Of course ...
80
votes
6answers
3k views

How to avoid nested With[]?

With[ {v1 = #}, With[ {v2 = f[v1]}, g[v1, v2] ] ] How to avoid nested With[] like the above? I'd like to use <...
5
votes
4answers
480 views

Expressions containing globally undefined symbols inside a function where they are defined

Consider the following code. f[a_,b_]:=x x=a+b; f[1,2] (* a + b *) From a certain viewpoint, one might expect it to return 3 ...
8
votes
1answer
516 views

Package functions and symbolic calculations

I'm writing my package (.m) in Mathematica and when I call the function it returns 0 instead of a right output. Here's my code: Package.m ...
48
votes
1answer
2k views

Local variables in Module leak into the Global context

From the Mathematica documentation on Module: Module allows you to set up local variables with names that are local to the module. But after using ...
47
votes
1answer
950 views

What does Internal`InheritedBlock do?

What does the function Internal`InheritedBlock do? How is it different from the regular Block?
15
votes
4answers
2k views

Subscripts - Why do I see the error “only assignments to symbols are allowed” when using a Module and not otherwise?

When I type Remove["Global`*"] foo[] := Module[{Subscript[a, 1] = "x"}, 0]; foo[] I get the expected error "only assignments to symbols are allowed". I ...
9
votes
4answers
884 views

How to set Block local variables by code?

I need to create a user-defined Block function where the Block variables' values are defined by code. For example, imagine I ...
23
votes
3answers
863 views

Nested definition: How can I define a function with a passed-in expression?

Here's a simplified version of what I'm trying to do: ...
55
votes
2answers
2k views

How safe is the use of Block and Internal`InheritedBlock

For many questions on this site answers are given which suggest to use Block and, especially for more advanced topics, ...
14
votes
2answers
3k views

Scoping in assigning a derivative

While answering another question, I stumbled upon a problem I cannot easily resolve. To assign the derivative of a function to another function, typically one can do this with a ...
41
votes
3answers
2k views

Why modules with no variables?

I was reading some code, in particular, recipe 4.13 on unification pattern-matching in Sal Mangano's Mathematica Cookbook, and there were many instances of Modules with no variables in them, such as ...
9
votes
1answer
418 views

Where does a package have to be loaded?

I'm trying to solve a very tricky issue in my function. The function needs the NDSolve`FEM` framework. Here is a minimal example: ...
13
votes
1answer
607 views

Do Table iteration variables need to be localized using Module?

Lets say I define a Module, that internally use iterating in a Table or Do, say something ...
7
votes
1answer
315 views

Creating a Block from a list of rules

How can I create a function which works like Block but takes a list of rules as its first argument, rather than a list of assignments? The function needs to be ...
28
votes
2answers
712 views

What is the purpose of Internal`LocalizedBlock?

I have come across the (internal) use of the function: Internal`LocalizedBlock I am trying to determine its purpose. It seem to behave like ...
29
votes
1answer
386 views

Strange behavior with Cases and Position with SetDelayed

I feel like I must be missing something simple and obvious here, but this has me scratching my head. This works as expected: ...
16
votes
2answers
1k views

Syntax highlighter shows error for Manipulate when it's inside a Block or a Module

I'm putting my new copy of Mathematica 10 through its paces and I noticed a weird change in the colouring scheme that I find very annoying, and I'd like to get some insight into why it's happening. ...
16
votes
1answer
443 views

StringReplace, ReplaceAll and Rule interact in a bizarre way

I have the following pair of things: ClearAll[foo, labeledFoo]; labeledFoo = {"FooBarBazQuux", foo}; This works like you'd expect: ...
13
votes
1answer
755 views

Context of localised (dynamic) symbols

When you localise a symbol with Module, the created unique symbol is usually in the current context. There seems to be an exception to this which has further ...
10
votes
4answers
459 views

Working with DynamicModule: ScheduledTasks with local variables

I have a question - is it possible to run ScheduleTask[] inside DynamicModule[]? What I have tried so far: ...
26
votes
4answers
921 views

SetOptions locally?

Is there a way to SetOptions locally? For example, I have a Module and inside it I am doing a lot of ...
9
votes
1answer
432 views

Variable scoping in Module

I don't understand why $a$ and $b$ are not local in the following code: ...
3
votes
1answer
384 views

Call Functions From File Without Modifying Context (Sandbox)

Let's say I have file named test.m containing test[arg1_] := ( Print[arg1];) What is the best technique for calling test like ...
21
votes
2answers
1k views

I define a variable as local to a module BUT then the module uses its global value! Why?

I have a question about modules and local variables. Here's my example: h = 5; Module[{a, h}, a[h_]= h^2; a[4]] (*Out[2] = 25*) I expected the module to ...
20
votes
3answers
1k views

Variable scope similar to other languages

Mathematica, unlike many other languages, defines the variables in the global scope unless it is explicitly asked to define a variable in a local scope, e.g., using ...
10
votes
0answers
890 views

Compile recursive function modifying global variables

How to compile recursive formula when it relies on more than a few global variables (global to the topmost compiled function)? It is unreasonable to pass on all such variables to each recursive ...
30
votes
1answer
863 views

Is the renaming mechanism of `With` flawed?

I'm confused about the renaming mechanism of With: ...
16
votes
3answers
2k views

What is the right way to construct DynamicModule

When I'm creating DynamicModules for CDF purposes I'm usualy basing on my experience with that, particular goal and content rather than on deep insight. I want to ...
18
votes
4answers
516 views

Internal DynamicModule steals scope of external DynamicModule

I have two dynamic objects, one nested in the other. Both have their own functions defined, as follows. I have simplified them to the point where they don't make much sense, but can still illustrate ...
13
votes
1answer
381 views

Is garbage collection broken in version 10.0.0?

Bug introduced in 10.0.0 and fixed in 10.0.1 In version 10.0.0 under Windows I am observing the following behavior: ...
17
votes
1answer
5k views

Returning a value from a Module

In the following simple example MyMod := Module[{i}, Do[ Return[1], {i, 3} ]; Print["test"] ] I expected the module to exit on ...
10
votes
3answers
638 views

Find variable name from DumpSave on a scoped variable

I saved an InterpolationFunction in a ".mx" files using DumpSave on a variable that was scoped by a ...
4
votes
1answer
406 views

ControlType -> None Vs. Module inside Manipulate (i.e. making everything local)

I'm building a program on another one made available in the Wolfram Demonstration Project. I've noticed that in the original code (working flawlessly) many variables were made local inside the ...
5
votes
2answers
1k views

Compute Hessian of function symbolically

This question could equally apply to the computation of other symbolic transformations of a function, but I use the Hessian as an example here. Consider a two-variable function ...
19
votes
3answers
792 views

How does $CellContext` work?

The only official info about $CellContext` I was able to find is: placeholder for the context of a symbol inside Dynamic ...
14
votes
4answers
484 views

Using With to scope over pure functions

Consider this example: given an option for a function func as "x" :> (a&), how can one assign different values to ...
9
votes
1answer
468 views

A smarter nested With?

I often find myself writing code that looks a bit like this: ...
8
votes
2answers
190 views

Using `With[…]` with a list specification as a variable [duplicate]

If you have some defined function, say f[a_, b_ c_, x], one can initialize this by using With[...] as ...
6
votes
4answers
242 views

How to scope `Pattern` labels in rules/set?

Module[{x}, f@x_ = x; p@x_ := x; {x, x_, x_ -> x, x_ :> x} ] ?f ?p gives ...
9
votes
3answers
859 views

How do I avoid scoping collisions of iterator variables?

Yesterday I had an issue that kept for quite a while. My code wasn't producing the right results. Now I know why and I am wondering how to avoid the issue in future. Consider the following code. <...
30
votes
2answers
3k views

What are some advanced uses for Block?

I read the answers to this question (What are the use cases for different scoping constructs?) and this one (Condition, Block, Module - which way is the most memory and computationally efficient?). ...
14
votes
2answers
274 views

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 ...
8
votes
1answer
324 views

Module variable scoping in Scheduled Tasks?

I ran across a scoping puzzle while experimenting with ScheduledTasks, and I'd be grateful for an explanation from the sages here. I found a workaround by intuitive horse sense, but was unable to ...
22
votes
1answer
437 views

Bug with iterated With: Referring to function arguments invalidates previous definitions

Thank you for your report. I have forwarded your report to the appropriate team for review. - WRI ...
9
votes
6answers
847 views

How can you give a Module a context and have its local variables and Modules belong to that context?

What would be the best way to give a module its own context and have its local variables and Modules belong to that context?
6
votes
0answers
345 views

Exhaustive examples of variable replacement due to nested scoping constructs

Consider the following examples, where I have replaced dollar signs in the output by a D. ...
5
votes
2answers
684 views

Why does the syntax highlighter color a local symbol red inside DynamicModule?

I am adding a Module inside DynamicModule here is an example (thanks to @rm-rf for this simple example) ...
8
votes
2answers
138 views

Cannot Block Plus

It is customary to use the following idiom to partially evaluate something inside a held expression: ...