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

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84
votes
7answers
3k 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: ...
22
votes
4answers
386 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 ...
28
votes
3answers
629 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 ...
10
votes
2answers
392 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 ...
7
votes
4answers
359 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 have: ...
2
votes
1answer
220 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 ...
7
votes
0answers
204 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 ...
7
votes
3answers
210 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. ...
34
votes
3answers
920 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 ...
12
votes
3answers
261 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 ...
5
votes
4answers
387 views

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
3answers
253 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 ...
6
votes
1answer
218 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 ...
5
votes
6answers
573 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?
11
votes
1answer
255 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 ...
3
votes
2answers
198 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) ...
18
votes
2answers
675 views

What are some advanced uses for Block?

I read the answer to this question and this one. According to those, Block is safer (if something aborts, it restores the values) and faster (perhaps something to ...
23
votes
1answer
204 views

What does Internal`InheritedBlock do?

What does the function Internal`InheritedBlock do? How is it different from the regular Block?
10
votes
2answers
210 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 ...
5
votes
0answers
106 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 ...
18
votes
1answer
196 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, ...
9
votes
2answers
217 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. ...
13
votes
1answer
243 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 ...
11
votes
4answers
279 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
119 views

What are the scoping rules for function parameters shadowing System` symbols?

Here are some very contrived code snippets, highly unlikely to appear in real code, but still I am curious why they behave like this: ...
4
votes
3answers
360 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 ...
4
votes
1answer
156 views

How to avoid conflicts between local variable names and symbolic arguments in Block constructs?

I am using Block inside the definition of some recursive functions. If the Block definitions use short variable names, like ...
9
votes
0answers
133 views

Compile not correctly initializing a variable defined inside Module

In the following example, inside the minimumX's Module, x is initialized to 1, but the ...
8
votes
1answer
117 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 ...
5
votes
1answer
129 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
102 views

How to inherit options by scoping?

Consider the following example: you have a function framed producing a cell with a button that, when pushed, calls framed again. ...
3
votes
3answers
92 views

Name scope confusion

Sorry for the too ambiguous title. First consider a following code snippet. ...
3
votes
2answers
162 views

How to declare a function that uses local variables of a module outside this module?

I have the following code Module[{f,x=0}, f[t_] := x + t; ..........; ...f[1]...; ..........; ] My aim is to put the declaration of the function ...
3
votes
1answer
134 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, ...
3
votes
2answers
224 views

LetL and Module efficiency

I was recently introduced to the LetL macro thanks to Leonid's answer to one of my prior questions. I was, needless to say, impressed by the simplicity of its ...
3
votes
2answers
317 views

Local variables

I'm trying to use Modules together with functions. tmp2 = x^2 + 1; f[y_] := Module[{x = 1}, Evaluate[y tmp2]] This works when ...
1
vote
1answer
124 views

Passing a joined list of symbols for Module or Block to treat as its own local symbols

The Question I'd like to write a function which itself takes a list of symbols, e.g. Foo[{x, y, z}] to pass to Module ...
0
votes
1answer
87 views

Why do InputFields not respond in Manipulate utilizing FindGeometricTransform?

In the following code changing the InputField does not result in observing changes in a result from FindGeometricTransform, but ...
0
votes
1answer
186 views

Passing lists to functions in a manner that works like pass-by-reference in other languages?

Is it possible to use a list as a variable, i.e., to pass it by reference to a function? In particular, I have a two-dimensional array and a function to get one element specified by its position: ...