Should I worry about a cmd opening and typing “echo off”?

I some days see a cmd.exe opening and typing “echo off”, then disappear.

My computer is slow, but I’m not sure if a program running with first line “echo off” would be so slow as to let me see it being typed… That’s a reason to believe it’s a person.

On the other hand, if someone else log into one’s pc, it will open a new session, so you’ll not see what he’s running, right?

I’m not sure if I should worry.

I’m running Windows 10.

Parentheses after Typing Environment

I’ve been reading about System F Omega lately, and I keep stumbling across a construct in typing rules that I cannot find an explanation of: Γ(x) = k. For example, in A Short Introduction to Systems F and F Omega:

Γ(a) = k -------- Γ ⊢ a : k 

I see the same construct in Hereditary Substitution for Stratified System F. I understand the bottom part fine. It would read something like: “In context Γ, a has kind k“. I’ve not been able to find an explanation of the top part, and the sources I referenced both assume familiarity with this construct. If I had to guess, I suspect that it means something like “In context a, running a kind-checking algorithm on a gives you kind k as the result”. Is that accurate? What online resources describe this construct?

Why is DNS apparently involved in typing “dir” on Windows 10?

For complicated reasons, I have been forced to make an identical copy of cmd.exe and rename it to cmd-2.exe, which I put a shortcut to in the Taskbar. The reason is purely to have them “grouped” in different “taskbar groups”, and nothing else.

Sometimes, I forget about this, and to open a new cmd.exe, I simply middle-click that Taskbar icon to open a new cmd.exe. Then I type a command such as “dir”, and then it spits out a bunch of nonsense, including:

DNS bad key. 

This only happens if I accidentally use the cmd-2.exe. Not if I open the “real” cmd.exe. So it’s not a “practical” problem.

However, I wonder why that message is ever printed at all. It’s apparently failing to do some kind of DNS lookup or something? Why is DNS involved at all with me typing “dir” to list files in my local computer? I have no network set up, no “cloud drives”, nothing like that whatsoever. It scares me that (apparently) there are DNS queries being made when I type “dir”.

Or maybe “DNS bad key” refers to something completely unrelated to the Domain Name System? I don’t know what a “bad key” would even be in that context…

Is the choice of static and dynamic typing not visible to the programmers of the languages?

From Design Concepts in Programming Languages by Turbak

Although some dynamically typed languages have simple type markers (e.g., Perl variable names begin with a character that indicates the type of value: $ for scalar values, @ for array values, and % for hash values (key/value pairs)), dynamically typed languages typically have no explicit type annotations.

The converse is true in statically typed languages, where explicit type annotations are the norm. Most languages descended from Algol 68 , such as Ada , C / C++ , Java , and Pascal , require that types be explicitly declared for all variables, all data-structure components, and all function/procedure/method parameters and return values. However, some languages (e.g., ML , Haskell , FX , Miranda ) achieve static typing without explicit type declarations via a technique called type reconstruction or type inference.

Question 1: For dynamically typed languages which “have no explicit type annotations”, do they need to infer/reconstruct the types/classes, by using some type/class reconstruction or type/class inference techniques, as statically typed languages do?

Question 2: The above quote says static or dynamic typing and explicit or no type annotations can mix and match.

  • Is the choice between static and dynamic typing only internal to the implementations of programming languages, not visible to the programmers of the languages?

  • Do programmers in programming languages only notice whether the languages use explicit type/class annotations or not, not whether the languages use static or dynamic typing? Specifically, do languages with explicit type/class annotations look the same to programmers, regardless of whether they are static or dynamic typing? Do languages without explicit type/class annotations look the same to programmers, regardless of whether they are static or dynamic typing?

Question 3: If you can understand the following quote from Practical Foundation of Programming Languages by Harper (a preview version is,

  • Do the syntax for numeral (abstract syntax num[n] or concrete syntax overline{n}) and abstraction (abstract syntax fun(x.d) or concrete syntax λ(x)d ) use explicit types/classes with dynamic typing?
  • If yes, is the purpose of using explicit types/classes to avoid type inference/reconstruction?

Section 22.1 Dynamically Typed PCF

To illustrate dynamic typing, we formulate a dynamically typed version of PCF, called DPCF. The abstract syntax of DPCF is given by the following grammar:

Exp d :: = x x variable            num[n] overline{n}      numeral            zero zero      zero            succ(d) succ(d)      successor            ifz {d0; x.d1} (d) ifz d {zero → d0 | succ(x) → d1}      zero test            fun(x.d) λ(x)d      abstraction            ap(d1; d2) d1 (d2)      application            fix(x.d) fix x is d      recursion 

There are two classes of values in DPCF, the numbers, which have the form num[n], and the functions, which have the form fun(x.d). The expressions zero and succ(d) are not themselves values, but rather are constructors that evaluate to values. General recursion is definable using a fixed point combinator but is taken as primitive here to simplify the analysis of the dynamics in Section 22.3.

As usual, the abstract syntax of DPCF is what matters, but we use the concrete syntax to improve readability. However, notational conveniences can obscure important details, such as the tagging of values with their class and the checking of these tags at run-time. For example, the concrete syntax for a number, overline{n}, suggests a “bare” representation, the abstract syntax reveals that the number is labeled with the class num to distinguish it from a function. Correspondingly, the concrete syntax for a function is λ (x) d, but its abstract syntax, fun(x.d), shows that it also sports a class label. The class labels are required to ensure safety by run-time checking, and must not be overlooked when comparing static with dynamic languages.


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Ubuntu changes line itself while typing with the built-in Keyboard

Ubuntu community,

I have a really disgusting trouble while typing with built-in keyboard on Ubuntu 16.04.06 LTS, the problem is that (I do not know why)while I am typing the line changes or it just delete everything and a lot of weird things, I re-installed the software, update it and nothing worked.

Have you any idea? help please.

Best regards, Santiago

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after typing stty raw -echo the terminal stuck and doesn’t work?

Not much to explain, I am basically practising some penetration testings, so I have spawned a low privilege shell, which is connected through nc. but now to get a properly working shell, as everyone says, I could do CTRL+Z > type stty raw -echo > fg, but when I do so, my terminal get stuck and when I type I just see my keyboard pointer blinking but doesn’t type anything, I don’t even know how to kill the terminal which is stuck in tmux.

prior to running stty raw -echo when I do ls -l /bin/bash I see:

lrwxr-xr-x  1 root  wheel  7 Jan  4  2014 /bin/bash -> /bin/sh 

Wolfram cloud and typing short cut

I subscribed Wolfram Cloud just a few days ago, and now I trying to get used to it.

I’m using iPad pro(gen 2) with the smart keyboard for it, and access on the Cloud via Wolfram cloud app.

But I’m struggling with typing subscription, power, fraction and Greek letters etc as on desktop environment.

I cannot use, for example, “ctrl(cmd maybe on Mac?) + _” to write subscript, and “ctrl + /” to convert a input into fractional form.

Also the short cut for escape key on iPad(which is “control + [”) does not work on the app, and others seem not to be alternatives, too.

May I ask anyone to confirm whether those issue could be resolved on (iPad+cloud app) environment? Should I wait for next update for it?

Thanks for reading.