@ -22,11 +22,11 @@
\DeclareCaptionFormat { underlinedfigure} { #1#2#3\hrulefill }
\captionsetup [figure] { format=underlinedfigure}
\usepackage [T1] { fontenc} % Fixes issues with accented characters
\usepackage [scaled=0.85] { beramono}
% \usepackage { libertine}
% \usepackage { lmodern}
% \usepackage { palatino}
% \usepackage { newpxtext,newpxmath}
\usepackage [scaled=0.85] { beramono}
\usepackage [activate=true,
final,
tracking=true,
@ -2204,24 +2204,36 @@ The (delimited) continuation of $\exit~1$ is effectively dead code.
\subsection { Dynamic binding: user-specific environments}
\label { sec:tiny-unix-env}
In \UNIX { } an environment maps keys to string-values. A key-value pair is
referred to as an \emph { environment variable} . Each user gets their
own environment with their own set of environment variables. Some
environment variable names are common to all environments, but their
valuation may depend on the particular user session. For example, the
environment variable \texttt { USER} is bound to the (string) name of
the user; the result of querying the environment for the value of
\texttt { USER} depends on which user session it is executed under.
When a process is run in \UNIX { } , the operating system makes available
to the process a collection of name-value pairs called the
\emph { environment} .
%
The name of a name-value pair is known as an \emph { environment
variable} .
%
During execution the process may perform a system call to ask the
operating system for the value of some environment variable.
%
The value of environment variables may change throughout process
execution, moreover, the value of some environment variables may vary
according to which user asks the environment.
%
\dhil { The value of an environment variable may also change during execution.}
For example, an environment may contain the environment variable
\texttt { USER} that is bound to the name of the inquiring user.
An environment variable is an instance of dynamic binding. The idea of
dynamic binding as a programming notion dates back as far as the
original implementation of Lisp~\cite { McCarthy60} .
An environment variable can be viewed as an instance of dynamic
binding. The idea of dynamic binding as a binding form in programming
dates back as far as the original implementation of
Lisp~\cite { McCarthy60} , and still finds uses in successors such as
Emacs Lisp~\cite { LewisLSG20} . It is well-known that dynamic binding
can be encoded as a computational effect by using delimited
control~\cite { KiselyovSS06} .
%
We will use dynamic binding to implement user-specific environments.
Unsurprisingly, we will use this insight to simulate user-specific
environments using effect handlers.
For simplicity we will fix the users to be root, Alice, and Bob.
For simplicity we fix the users of the operating system to be root,
Alice, and Bob.
%
\[
\User \defas [\Alice ;\Bob ;\Root ]
