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Questions tagged [scoping]

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

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218
votes
8answers
12k 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: ...
78
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 <...
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, ...
46
votes
4answers
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 ...
44
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 ...
43
votes
1answer
823 views

What does Internal`InheritedBlock do?

What does the function Internal`InheritedBlock do? How is it different from the regular Block?
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 ...
29
votes
1answer
838 views

Is the renaming mechanism of `With` flawed?

I'm confused about the renaming mechanism of With: ...
28
votes
2answers
2k 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?). ...
27
votes
2answers
656 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 ...
27
votes
1answer
335 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: ...
24
votes
1answer
453 views

Bug with Block & Lookup: Scope Variable Leak

After debugging a large chunk of code, I could identify this MWE. ...
23
votes
4answers
709 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 ...
23
votes
3answers
754 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: ...
23
votes
0answers
401 views

Compile not correctly initializing a variable defined inside Module

Bug introduced in 8.0, fixed in 10.4, intentionally reintroduced in 11.0 and persisting through 12.0. In the following example, inside the minimumX's ...
22
votes
1answer
8k views

Module with “local functions”

I am trying to use a Module having "local functions", i.e., those which I need to define only inside this module. So I tried this: ...
21
votes
2answers
549 views

Should I always be using Module in functions unless I explicitly want global variables?

I define functions a ton. In the past, I've mostly just defined my functions like: myFunc[var1_]:=( var2=var1^2; Return@var2; ) And I haven't run into too ...
21
votes
1answer
422 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 ...
21
votes
1answer
260 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, ...
21
votes
1answer
408 views

ClearAll::clloc - “Cannot clear local variable x” in Block[{x}, …] - why?

Block[{x}, ClearAll@x] ClearAll::clloc: Cannot clear local variable x. The documentation just says An error occurs because ClearAll cannot be used with a ...
20
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
2answers
794 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 ...
20
votes
1answer
270 views

Integrate - Why is the integration variable not local

I have noticed something odd: Let f[t_]:=Integrate[x, {x, 0, t}] h[t_]:=Sum[x, {x, 0, t}] Now, enter ...
18
votes
4answers
451 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 ...
18
votes
3answers
601 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 ...
18
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 ...
18
votes
1answer
394 views

A With expression local variable specification without head List

I just noticed a new form of With in its documentation: With[$x=x_0$, $expr$] specifies that all occurrences of the symbol $x$ in $expr$ should be replaced ...
17
votes
1answer
4k 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 ...
17
votes
2answers
428 views

Messages leak out from Block

Bug introduced in 8.0 or earlier and fixed in 10.1 When assigning message to a symbol localized by Block, I would expect that this message is not accessible ...
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
413 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: ...
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 ...
16
votes
1answer
422 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 ...
15
votes
2answers
466 views

Why can't I inject expressions in Compile using (only) With

Generally speaking, With can be used to inject into arbitrarily held expressions, for example: ...
15
votes
1answer
485 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 ...
15
votes
0answers
181 views

Why are delayed definitions in scoping functions NOT documented?

As outlined here, := may be used in scoping constructs like With to give delayed definitions, but this is undocumented. This ...
14
votes
4answers
449 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 ...
14
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 ...
14
votes
2answers
458 views

Is Mathematica's lexical scoping broken?

Why do these two lines output different things (b and 0, respectively)? Is it a bug? ...
14
votes
1answer
114 views

Bug when combining Dataset with a scoping construct and Map

The following fails in v11: ...
14
votes
2answers
238 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 ...
13
votes
2answers
2k 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 ...
13
votes
1answer
639 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
144 views

Unexpected optimization with With

I do not understand why the function With[{y = #}, {y, y, y}] & maps faster than the function {#, #, #} &. The ...
13
votes
1answer
365 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: ...
12
votes
2answers
321 views

RecurrenceTable iteration variable not localized? Bug or user error?

I recently lost a lot of time on this and need to understand whether I have misunderstood MMA operations or there's a problem. I am using MMA 10.1 on Windows 7 64-bit. The essence of the issue is ...
12
votes
1answer
269 views

Working with DynamicModule: SetDelayed + OwnValues

Shortly, definitions in form of e.g. x:= RandomReal[] have to be avoided inside DynamicModule[{x}, ...]. Why?, this ...
12
votes
2answers
173 views

Bug: With[] pattern-variable renaming misses symbols within `Except`

Bug introduced in 10.1 and fixed in 11.1 Thank you for taking the time to send in this report. It does appear that pattern-variable renaming misses symbols within Except when using With. I will ...
12
votes
1answer
422 views

Temporary variable not removed in Mathematica 10

Bug introduced in 10.0.1 and fixed in 10.0.2 In Mathematica 10, the documentation still states that a symbol with attribute Temporary will automatically be removed ...
11
votes
4answers
533 views

Using predefined expressions as free variables in a pure function [duplicate]

I want to have a function value of an expression where some variables are solutions to some set of equations, with some values of parameters. I had an idea to use pure functions for that. However, ...