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JavaScript lexical environments as objects


JavaScript lexical environments as objects

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JavaScript lexical environments as objects
Tag : javascript , By : Jesenko Mehmedbasic
Date : November 28 2020, 04:01 AM

seems to work fine There is one important distinction where the analogy breaks down: lexical environments are created from static code analysis, and do not change their shape. They are records, not dynamic objects. This both helps the interpreter/compiler to optimise lookups, and prevents them from being exposed as objects.
There are only two little things that introduce dynamic scoping: eval and with. (The latter allows to actually put dynamic objects in the scope chain). They're both despised because of this.

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How to create a lexical analyzer in ANTLR 4 that can catch different types of lexical errors


Tag : java , By : Raghaw
Date : March 29 2020, 07:55 AM
Does that help Create an error token rule for each known error and an "catchall" error token rule at the end like this:
// valid tokens first!
Number : [0-9]+;
Identifier : [a-zA-Z] [a-zA-Z0-9]*;
//...

// "error" tokens
// don't use these tokens in your grammar; They will show up as extraneous tokens during parsing and can be handled if desired.
InvalidIdentifier : [0-9]([0-9a-zA-Z])+; 
ACommonInvalidToken : '^'; // if you want to be more specific for certain cases
// add more to address common mistakes

UnknownToken : . ; // the "catch-all" error token; be sure not to be too greedy...

JavaScript: how are functions and their scopes/lexical environments passed around?


Tag : javascript , By : Mariamario
Date : March 29 2020, 07:55 AM
I hope this helps . Yes, functions do only have access to their own lexical environment - from where they were defined. JavaScript does not have dynamic scope where a function has any kind of access to the scope where it is called.
This happens by attaching the scope to the function object, it is a part of the closure.

ignore parent/ancestor environments inside function (disable lexical scoping)


Tag : r , By : user183825
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further You can set the environment of your function to be the baseenv() which will not search the global environment
x <- 1
f <- function() return(x);
environment(f) <- baseenv()
f() 
# Error in f() : object 'x' not found
x <- 1
f <- function() 
  eval(parse(text = "x"), 
       envir = baseenv())
f()
# Error in eval(expr, envir, enclos) : object 'x' not found

Lexical Scoping and sharing objects


Tag : development , By : Reiner
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further Your points 2 to 5 are correct. In your point 1, f and make-account do not "have" pointers to global environment - they do not need to, by themselves. They are both entries, bindings, in the global environment. Both "refer to", or "point at" simple values, functions in both cases.
bank-account with respect to e2 actually points to the value to which paul-acc points (which is the same value to which peter-acc points, or refers). In Scheme, (define n1 n2) means "set up new binding in the current environment, named n1, and pointing at the value of the expression n2". If n2 happens to be a variable, its value is just what that variable's value is. That's why we're talking about Scheme's evaluation semantics.
( (lambda (param) body) arg )
=
(let ( (param arg) )
   body)

Where in the ECMAScript specification can we find exactly when new Lexical Environments are created?


Tag : javascript , By : lili
Date : March 29 2020, 07:55 AM
seems to work fine 8.1.2.2 - 8.1.2.6 are the ways that a new lexical environment is created. You can find all the places those are used in the spec by searching for the name.
Eg. if you search for NewFunctionEnvironment, you will find that one is created in 9.2.1.1 PrepareForOrdinaryCall. There is only one place in the spec where each of Global, Module, Function, and Object environments are created. There are several places where Declarative environments are created.
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