Lexical scoping (sometimes known as static scoping ) is a convention used with many programming languages that sets the scope (range of functionality) of a variable so that it may only be called (referenced) from within the block of code in which it is defined. The scope is determined when the code is compiled. A variable declared in this fashion is sometimes called a private variable.
Questions tagged [lexical-scope]
271 questions
4
votes
1 answer
Elisp: Symbol's value as variable is void with let* and (lambda)
Disclaimer: I started to hack around with elisp today.
I am really wondering what I am getting the following error:
Symbol's value as variable is void: response
with the following code:
(let* ((response (cons 'dict nil)))
(nrepl-request:eval
…
Neoasimov
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4
votes
4 answers
In Perl, do "$a" and "$b" have any special use outside of the sort() function?
I asked a question about the use of "$a" and "$b" in Perl's sort() function the other day:
What exactly are "$a" and "$b" in Perl's "sort()" function?
I now have a follow up question. Are "$a" and "$b" only used by sort() or is there any other Perl…
tjwrona1992
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4
votes
1 answer
Lexical scoping in C# lambda/anonymous delegates
I want to check whether a simple mathematical expression would overflow (using checked and catch(OverflowException)), but without the need to use a try-catch block every time. So the expression (not the result!) should be passed to a function…
AndiDog
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4
votes
1 answer
What's the logic behind this python global scoping magic?
I was messing around with the scoping in python and found something that I think is rather strange:
g = 5
def foo(a):
if a:
global g
g = 10
else:
g = 20
print("global g: ",g)
foo(False)
print("global g: ",g) #…
monoceres
- 4,722
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4
votes
2 answers
Does emacs lisp support lexically redefining a function?
Recent versions of Emacs support lexical binding for variables in elisp code. Is it also possible to lexically redefine functions? In other words, does Emacs Lisp have something like lexical-flet?
Ryan C. Thompson
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3
votes
1 answer
Does the inner function know that a variable is inside the temporal dead zone before searching further through the scope chain?
function b() {
function a() {
console.log(x);
}
a();
const x = 10;
}
const x = 20;
b()
If I understand lexical scoping and execution context correctly, when function a() is invoked, it should have a reference to b's…
james
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3
votes
0 answers
R package to extract minimal code required to reproduce a result
A trivial example. Let's say this is the original code:
x = 1
y = 2
z = x * 3
If we specify that we want to reproduce z, then the package would return a new script containing only the lines of code required to generate the value z.
x = 1
z = x *…
D Greenwood
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- 2
- 11
3
votes
1 answer
Why does using a variable in a function change the value returned in R when using superassignment (<<-) operator?
Why do bar and baz behave differently? When bar is called both the value of a printed and the value of a in the global scope are the same, but when baz is called the printed value and the value in the global scope are different. Seemingly, the only…
seaFan
- 116
- 5
3
votes
1 answer
Perl replace value without updating array
I have the following Perl script.
#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;
my @fruits = qw(apple banana orange pear);
print Dumper \@fruits;
foreach my $fruit (@fruits) {
$fruit =~ s|apple|peach|;
}
print Dumper…
JeremyCanfield
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3
votes
2 answers
Struggling with lexical scoping and for loops
How do I get the modify_attr() function (below) not to capture/update the value of b in the following for loop? (simplified version, occurring within a mainloop()):
for b in range(x):
button = tk.Button(button_frame, text="<", command=lambda:…
Nathan
- 118
- 6
3
votes
1 answer
R - Checking if a string is a valid mathematical expression using non-standard evaluation
I would like to check if the strings below are valid mathematical expressions:
s1 = 'sin(x)'
s2 = 'sin(x*m)'
s3 = 'sin'
s4 = 'sin(xm)'
By 'valid', I mean the expression is a combination of
operators (must be used in conjunction with variables or…
user51462
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- 41
3
votes
1 answer
The code outputs a number instead of undefined?
According to my understanding, the code below should output undefined when I call hi() but instead it logs a number. I'm using chrome. Can somebody elaborate why is this happening? Thanks in advance.
Screen shot of Code:
const obj = {
name:…
aaKhan
- 247
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- 16
3
votes
2 answers
Why does jQuery has a "window=this" at the very begining and say it would speed up references to window?
When I open jQuery's source code I find this line.
var
// Will speed up references to window, and allows munging its name.
window = this
Why and how this line will speed up?
David
- 133
- 5
3
votes
2 answers
difference between let inside and outside a lambda expression
Consider a module with the following procedures:
(define-module (test test)
#:export (proc1 proc2 proc3))
(define proc1
(let ((module (current-module)))
(lambda ()
(format #t "~s\n" module))))
(define proc2
(lambda ()
(let…
Ernest A
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- 40
3
votes
1 answer
Understanding the environment model of evaluation
Exercise 3.20 in SICP:
Draw environment diagrams to illustrate the evaluation of the sequence
of expressions
(define x (cons 1 2))
(define z (cons x x))
(set-car! (cdr z) 17)
(car x) 17
using the procedural implementation of pairs given…
lightning_missile
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