Review Questions 235
Scalar variables can be separated into four categories by considering their
lifetimes: static, stack dynamic, explicit heap dynamic, and implicit heap dynamic.
Static scoping is a central feature of ALGOL 60 and some of its descen-
dants. It provides a simple, reliable, and efficient method of allowing visibility
of nonlocal variables in subprograms. Dynamic scoping provides more flex-
ibility than static scoping but, again, at the expense of readability, reliability,
and efficiency.
Most functional languages allow the user to create local scopes with let
constructs, which limit the scope of their defined names.
The referencing environment of a statement is the collection of all of the
variables that are visible to that statement.
Named constants are simply variables that are bound to values only once.
REVIEW QUESTIONS
- What are the design issues for names?
- What is the potential danger of case-sensitive names?
- In what way are reserved words better than keywords?
- What is an alias?
- Which category of C++ reference variables is always aliases?
- What is the l-value of a variable? What is the r-value?
- Define binding and binding time.
- After language design and implementation [what are the four times bind-
ings can take place in a program?]
- Define static binding and dynamic binding.
- What are the advantages and disadvantages of implicit declarations?
- What are the advantages and disadvantages of dynamic type binding?
- Define static, stack-dynamic, explicit heap-dynamic, and implicit heap-
dynamic variables. What are their advantages and disadvantages?
- Define lifetime, scope, static scope, and dynamic scope.
- How is a reference to a nonlocal variable in a static-scoped program con-
nected to its definition?
- What is the general problem with static scoping?
- What is the referencing environment of a statement?
- What is a static ancestor of a subprogram? What is a dynamic ancestor
of a subprogram?
- What is a block?
- What is the purpose of the let constructs in functional languages?
- What is the difference between the names defined in an ML let con-
struct from the variables declared in a C block?
