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

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153
votes
7answers
7k 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: ...
36
votes
4answers
953 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 ...
59
votes
6answers
2k 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 <...
2
votes
2answers
169 views

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

Consider the following code. f[a_,b_]:=x; Clear[a,b]; x=a+b; f[1,2] It returns a+b. However, from a certain viewpoint, one ...
40
votes
1answer
1k 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 ...
9
votes
4answers
585 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 ...
22
votes
3answers
496 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: ...
11
votes
2answers
1k 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 ...
6
votes
1answer
201 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 ...
12
votes
2answers
679 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. ...
39
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 ...
30
votes
1answer
410 views

What does Internal`InheritedBlock do?

What does the function Internal`InheritedBlock do? How is it different from the regular Block?
10
votes
0answers
589 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 ...
11
votes
4answers
923 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 ...
3
votes
1answer
315 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 ...
15
votes
2answers
379 views

What is the purpose of Internal`LocalizedBlock?

I have come across the (internal) use of of the function: Internal`LocalizedBlock I am trying to determine its purpose. It seem to behave like ...
15
votes
3answers
619 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 ...
13
votes
1answer
323 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 ...
13
votes
1answer
327 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: ...
8
votes
3answers
593 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. <...
11
votes
3answers
987 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 ...
19
votes
2answers
551 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 ...
7
votes
1answer
281 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 ...
14
votes
3answers
276 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 ...
7
votes
6answers
638 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?
9
votes
1answer
307 views

Variable scoping in Module

I don't understand why $a$ and $b$ are not local in the following code: ...
8
votes
1answer
322 views

A smarter nested With?

I often find myself writing code that looks a bit like this: ...
4
votes
4answers
151 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 ...
10
votes
3answers
384 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 ...
3
votes
2answers
407 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) ...
4
votes
1answer
183 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 ...
15
votes
1answer
421 views

Is the sharing of variables in Module/Block within Compile documented behavior?

Today I noticed something, I think for the first time. When used inside Compile variable values within Module (and ...
10
votes
2answers
308 views

Strange results while nesting scope constructs?

I did a handful of tests with Block, With, and Module and had a couple of new surprises. ...
6
votes
1answer
201 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: ...
23
votes
1answer
228 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
1answer
368 views

Modules that initialize themselves on first call

I use a lot of functions that extract a specific data item from a file with many data items. I want these functions to load data (slow) and return the item (fast) on first call, but just return the ...
5
votes
0answers
244 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. ...
13
votes
4answers
362 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 ...
10
votes
1answer
145 views

Is it possible to use the global definition of a symbol as part of its new local definition set in a Block?

Consider the following expression: Block[{Print = CopyToClipboard}, doSomething[]] Now all calls to Print from ...
8
votes
1answer
408 views

Treat all variables as local in a module [duplicate]

In most languages, any variable defined inside a function is considered local. ...
4
votes
1answer
128 views

Defining a function that prints both the name and value of a variable defined locally within the calling function

To save time when debugging with Print statements, I'd like to define a function -- call it PrintVal -- that prints both the name and value of a variable defined locally within the calling function. ...
4
votes
3answers
345 views

Altering values in Manipulate with dynamically generated controls

I have a Manipulate whose controls are generated based on a parameter in a containing Manipulate: ...
3
votes
1answer
169 views

Issue with scope of variables

For the definitions, t = 1; f[x_, y_] := t (x + y); v[3] := {1, 1}; g[u_] := f[v[u][[1]], v[u][[2]]]; the following two expressions yield different results, ...
1
vote
1answer
58 views

Module and Manipulate: Why the Red Highlighting? [duplicate]

If I define a function that returns a Manipulate object, and the Manipulate has a local variable inside of it, the local ...
24
votes
2answers
1k 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?). ...
17
votes
2answers
478 views

Module trash collection behaviour

I have asked this question before on the Wolfram community forum (http://community.wolfram.com/groups/-/m/t/83845?p_p_auth=Gxoxe65B) but not with great success. Module creates temporary variables of ...
10
votes
2answers
360 views

Avoiding MainEvaluate in a CompiledFunction to fetch global variables

I'm trying to write a simulation using Mathematica 8.0. Since I will most likely be doing the same operation over and over again, I'm trying to Compile whatever I ...
20
votes
1answer
235 views

“With” as part of the “Dynamic Interactivity Language”

I noticed that in Mathematica's Function Navigator With is listed as being part of the "Dynamic Interactivity Language". It is not the first (or even the fourth, ...
10
votes
2answers
372 views

Localizing variables within a Manipulate

I have a notebook with several examples of very similar computations, each involving the same variable/parameter names of the ingredients used in a final Manipulate....
5
votes
0answers
129 views

Are there any videos that show how different Mathematica expressions are evaluated?

Are there any videos that show how different Mathematica expressions are represented internally as object graphs and demonstrate how they are transformed during an evaluation? I am asking because I ...