Section 1
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Actual/Formal Parameter
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Section 1
(50 cards)
Actual/Formal Parameter
Positional- first to first, safe and effective ; Keyword by same name, advantages-Parameters can appear in any order, thereby avoiding parameter correspondence errors, Disadvantages-User must know the formal parameter's names
Functional
a style of building the structure and elements of computer programs—that treats computation as the evaluation of mathematical functions and avoids changing-state and mutable data
Algol
ALGOrithmic Language, mid-1950s, rise to BCPL, B, Pascal, PL/I, Simula, C and more. Developed jointly by a committee of European and American computer scientists in a meeting in 1958, Three different syntaxes: a reference syntax, a publication syntax, and an implementation syntax
Exception Handling
Intercept run-time errors and take corrective measures; make program robust
Case sensitivity identifiers
What are these advantages to? -Variable identifiers may look different than identifiers that are names for constants -It greatly increases the space of total possible variable names
flaws in software in 1970s
lack type checking; inadequacy in control statements
Dynamic scoping disadvs
Poor readability (can't determine type from code); Unintended consequences; Cannot type-check at compile time.
Concurrent
form of computing in which several computations are executing during overlapping time periods—concurrently—instead of sequentially (one completing before the next starts)
Coroutines
a subprogram that has multiple entries and controls them itself - supported directly in Lua; called symmetric control; repeatedly resume each other
Imperative
uses statements that change a program's state. In much the same way that the imperative mood in natural languages expresses commands, an imperative program consists of commands for the computer to perform; designed for von-Neuman
interpreted language
entire process must be repeated every time the program is run, even if the code did not change; executes the program step-by-step; ability to modify programs during runtime by adding or changing functions; avoids explicit program compilation and translation happens 'on-the-fly'; slower to execute because each statement is read and executed by another program
Expressivity
"A set of relatively convenient ways of specifying operations, Strength and number of operators and predefined functions
Fortran
by IBM in the 1950s; proposed by John W. Backus Scientific applications (over 50 years), floating point computations and arrays; first widely used programming language supported across a variety of computer architectures
Ada
by Jean Ichbiah of CII Honeywell Bull under contract to the United States Department of Defense in 1977 to 1983; strong typing, modularity mechanisms (packages), run-time checking, parallel processing exception handling, and generics. Ada 95 added support for object-oriented programming, including dynamic dispatch.
fully qualified reference
fully qualified reference to a record field is one in which all intermediate record name, from teh largest enclosing record to the specific field, are named in the reference; must include all record names
Functions Design Issues
Are side effects allowed?Parameters should always be in-mode to reduce side effect (like Ada)?What types of return values are allowed?Most imperative languages restrict the return types, C allows any type except arrays and functions, C++ is like C but also allows user-defined types, Java and C# methods can return any type (but because methods are not types, they cannot be returned), Python and Ruby treat methods as first-class objects, so they can be returned, as well as any other class, Lua allows functions to return multiple values
Data Abstraction
encapsulates the data and its associated processes together and also controls access to data
Basic
By John G. Kemeny and Thomas E. Kurtz in 1964, Enable students in fields other than science and mathematics to use computers, Microcomputers, for the Dartmouth Time-Sharing System, based on FORTRAN II, with some influences from ALGOL 60.
mixed-mode
can have operands of different types
coercion
An implicit type conversion ; Disadvantage-They decrease in the type error detection ability of the compiler
Associative Arrays
Design issues:What is the form of references to elements?Is the size static or dynamic?
Language Evaluation Criteria
Readablitiy, Writability, Reliability, Cost, Portability, Generality, Well-definedness
Metaprogramming
the writing of computer programs with the ability to treat programs as their data. It means that a program could be designed to read, generate, analyse or transform other programs, and even modify itself while running
C
By Dennis Ritchie between 1969 and 1973 at AT&T Bell Labs; Systems programming; Unix written in C; standardized by the American National Standards Institute and International Organization for Standardization; imperative (procedural) language; not initially designed with portability in mind.
dynamic binding
if binding it first occurs during run time begins and can be changed throughout program execution.
Case sensitive identifiers
What are these disadvantages to? -Allows programmers to create variable names that are similar to keywords, which makes the program harder to read -Programmers can make variables with names that look very similar
Iterative Statements
The repeated execution of a statement or compound statement is accomplished either by iteration or recursion; Design issues for iteration control statements:How is iteration controlled?Where is the control mechanism in the loop?
Deep binding
The environment of the definition of the passed subprogram, Most natural for static-scoped languages
Control Structure
a control statement and the statements whose execution it controls
Closures
A subprogram and the referencing environment where it was defined -only needed if a subprogram can access variables in nesting scopes and it can be called from anywhere
Aliasing
Presence of two or more distinct referencing methods for the same memory location; is known to decrease the reliablility of programs
Array
Design Issues:What types are legal for subscripts?Are subscripting expressions in element references range checked?When are subscript ranges bound?When does allocation take place?Are ragged or rectangular multidimensional arrays allowed, or both?What is the maximum number of subscripts?Can array objects be initialized?Are any kind of slices supported?
elliptical reference
When the referencing can omit any or all of the enclosing record names, as long as the resulting reference is unambiguous.
denotational semantics
each phrase in the language is interpreted as a conceptual meaning that can be thought of abstractly
dynamically typed
The type of all variables within the program is determined at runtime and can vary.; Advantages-Support for recursion, Storage for locals is shared among some subprograms; Disadvantades-Allocation/deallocation, initialization time, Indirect addressing, Subprograms cannot be history sensitive
Cost
Training programmers; Writing programs; Compiling programs; Executing programs; Language implementation system: availability of free compilers; Reliability: poor reliability leads to high costs; Maintaining programs
Generality
The applicability to a wide range of applications
Counter-Controlled Loops
A counting iterative statement has a loop variable, and a means of specifying the initial and terminal, and stepsize values; Design Issues:What are the type and scope of the loop variable?Should it be legal for the loop variable or loop parameters to be changed in the loop body, and if so, does the change affect loop control?Should the loop parameters be evaluated only once, or once for every iteration?
Enumeration Types
enum days {mon, tue, wed, thu, fri, sat, sun}; Design issues-it constant allowed to appear in more than one type definition, and if so, how is the type of an occurrence of that constant checked?Are its values coerced to integer?Any oter type coerced to an enumeration type?
arithmetic expressions
Design issues-Operator precedence rules?Operator associativity rules?Order of operand evaluation?Operand evaluation side effects?Operator overloading?Type mixing in expressions?
event-driven
a programming paradigm in which the flow of the program is determined by events such as user actions (mouse clicks, key presses), sensor outputs, or messages from other programs/threads; used in graphical user interfaces
COBOL
by CODASYL 1959; Business applications (over 50 years), Reports, decimal numbers and characters; standardized in 1968; imperative, procedural and, since 2002, object-oriented
Logically-Controlled Loops
Repetition control is based on a Boolean expression; Design issues:Pretest or posttest?Should the logically controlled loop be a special case of the counting loop statement or a separate statement?
Ad hoc binding
The environment of the call statement that passed the subprogram
declarative
a style of building the structure and elements of computer programs—that expresses the logic of a computation without describing its control flow
LISP
by John McCarthy in 1958; Artificial intelligence, pioneered many ideas in computer science, including tree data structures, automatic storage management, dynamic typing, conditionals, higher-order functions, recursion, and the self-hosting compiler; homoiconicity
Logic
set of sentences in logical form, expressing facts and rules about some problem domain; include Prolog, Datalog. In all of these languages, rules are written in the form of clauses:
Guarded Commands
each line in the selection statement, consisting of a Boolean expresion (a guard) and a statement of statement sequence
dangling pointer
pointing to a heap-dynamic variable which has be deallocated; Problem: Tombstone: extra heap cell that is a pointer to the heap-dynamic variable, The actual pointer variable points only at tombstones, When heap-dynamic variable de-allocated, tombstone remains but set to nil, Costly in time and space ; Locks-and-keys: Pointer values are represented as (key, address) pairs, Heap-dynamic variables are represented as variable plus cell for integer lock value, When heap-dynamic variable allocated, lock value is created and placed in lock cell and key cell of pointer
associativity of the $ and #
<tac> → <tic> $ <tac> (right) ; <tic> → <tic> # <toe> (left)
Section 2
(50 cards)
Shallow binding
The environment of the call statement that enacts the passed subprogram, Most natural for dynamic-scoped, languages
Pass-by-Value (in mode)
Disadvantages (if by physical move): additional storage is required (stored twice) and the actual move can be costly (for large parameters); Disadvantages (if by access path method): must write-protect in the called subprogram and accesses cost more (indirect addressing)
Overloaded Subprograms
DisAdvantages= Users can define nonsense operations, Readability may suffer, even when the operators make sense
Multiple-Way Selection Statements
Design Issues:What is the form and type of the control expression?How are the selectable segments specified?Is execution flow through the structure restricted to include just a single selectable segment?How are case values specified?What is done about unrepresented expression values?
Subtype polymorphism
means that a variable of type T can access any object of type T or any type derived from T (OOP languages)
subprogram Function declarations
In C and C++ are often called prototypes; A subprogram declaration provides the protocol, but not the body, of the subprogram
static binding
if binding first occurs before run time begins and remains unchanges throughout program execution.
Record Types
Design issues:What is the syntactic form of references to the field? Are elliptical references allowed
numeric type
booleans; ints and floating-ponte have it built from the bit type.
non-deterministic
the method of choice between these alternatives is not directly specified by the programmer
single language for all programming domains
It would justify the development of numerous language dependent software development aids; It would simplify programmer recruiting; It would increase code portability; It would dramatically cut the costs of programming training
Smalltalk
product of research led by Alan Kay at Xerox Palo Alto Research Center, object-oriented, dynamically typed, reflective programming language, Simula-like class inheritance model of execution, everything is an object
Object-Oriented
based on the concept of "objects", which may contain data, in the form of fields, often known as attributes; and code, in the form of procedures, often known as methods; fundamentals 1.Date Abstraction 2.Inheritance 3. Dynamic method binding or polymorphism
polymorphism
the ability in computer programming to present the same programming interface for differing underlying forms (data types, classes)
Pass-by-Value-Result (inout Mode)
combination of pass-by-value and pass-by-result; Disadvantages-Those of pass-by-result and Those of pass-by-value
Support for abstraction
The ability to define and use complex structures or operations in ways that allow details to be ignored
Orthogonality
Small set of primitive constructs can be combined in a relatively small number of ways; Every possible combination is legal; ex. Logic and arithmetic expressions can be intermixed; VAX used it as design criterion
Unions Types
Variables are allowed to store different type values at different times during execution; require that each union include a type indicator called a discriminant; Design issue:Should type checking be required?
Pointers
Design Issues:What are the scope of and lifetime of a pointer variable?What is the lifetime of a heap-dynamic variable?Are pointers restricted as to the type of value to which they can point?Are pointers used for dynamic storage management, indirect addressing, or both?Should the language support pointer types, reference types, or both?
subprogram formal parameter
a dummy variable listed in the subprogram header and used in the subprogram
Readablitiy
Overall simplicity, Orthogonality, Data types, Syntax considerations; easy to read code has more re-usablility
subprogram header
the first part of the definition, including the name, the kind of subprogram, and the formal parameters
referential transparency
The ability to substitute expressions of equal value and have the program produce the same result, Advantages-Semantics of a program is much easier to understand if it has referential transparency
Simula
By Ole-Johan Dahl and Kristen Nygaard in 1960s, first object-oriented, simulating discrete event systems, SIMULA standardized by Standards Group in Feb 1968.
subprogram actual parameter
represents a value or address used in the subprogram call statement
Pass-by-Name (Inout Mode)
Formals are bound to an access method at the time of the call, but actual binding to a value or address takes place at the time of a reference or assignment
Pass-by-Reference (Inout Mode)
Advantage: Passing process is efficient (no copying and no duplicated storage); Disadvantages, Slower accesses (compared to pass-by-value) to formal parameters, Potentials for unwanted side effects (collisions), Unwanted aliases (access broadened)
Portability
The ease with which programs can be moved from one implementation to another
Reliability
Type checking, Exception handling, Aliasing, Readability and writability; if under all condition, the program performs according to its specifications
Reference Counter
Reference counters: maintain a counter in every cell that store the number of pointers currently pointing at the cell; Disadvantages: space required, execution time required, complications for cells connected circularly; Advantage: it is intrinsically incremental, so significant delays in the application execution are avoided
short circuit evaluation
Determining the value of a boolean expression without needing to use all of the operators
subprogram parameter profile
(aka signature) of a subprogram is the number, order, and types of its parameters
Type Checking
Testing for type errors; important to maintain the reliability of the code.
Typeless language advantages
easier to learn as a first programming language; provides great flexibility for the programmer; useful for very low-level languages used for systems programming; Programmers can make changes to existing code in less time
statically typed
The type of all variables within the program is set at compile time. Advantages and disadvantages are the opposite of those for stack-dynamic local variables
subprogram
"two categories 1.Procedures are collection of statements that define parameterized computations 2.Functions structurally resemble procedures but are semantically modeled on mathematical functions"
selection statement
"provides the means of choosing between two or more paths of execution; Two general categories 1.Two-way selectors- if, then,else... 2. Multiple-way selectors, switch , case, default...case, then, else, end...Allow the selection of one of any number of statements or statement groups"
Two-Way Selection Statements
Design Issues:What is the form and type of the control expression?How are the then and else clauses specified?How should the meaning of nested selectors be specified?
User-Located Loop Control
"break"; Design issues for nested loops, Should the conditional be part of the exit?Should control be transferable out of more than one loop?
Scripting Languages
"smaller with relatively simple syntax and semantics; support libraries (usually) need not be nearly as large; easier to create and write a new language; focused on specific domains or more narrow applications; faster to develop smaller projects"
Simplicity
Manageable set of features and constructs , Minimal feature multiplicity and operator overloading
Syntax considerations
Identifier forms: flexible composition, Special words and methods of forming compound statements, Form and meaning: self-descriptive constructs, meaningful keywords
scripting
programs written for a special run-time environment that automate[1] the execution of tasks that could alternatively be executed one-by-one by a human operator
subprogram protocol
a subprogram's parameter profile and, if it is a function, its return type
PL/I
designed for scientific, engineering, business and system programming uses; data processing, numerical computation, scientific computing, and system programming; it supports recursion, structured programming, linked data structure handling, fixed-point, floating-point, complex, character string handling, and bit string handling; The first compiler was delivered in 1966. The Standard for PL/I was approved in 1976
Subprograms Design Issues
Are local variables static or dynamic? Can subprogram definitions appear in other subprogram definitions? What parameter passing methods are provided?Are parameter types checked?If subprograms can be passed as parameters and subprograms can be nested, what is the referencing environment of a passed subprogram?Are functional side effects allowed?What types of values can be returned from functions?How many values can be returned from functions?Can subprograms be overloaded?Can subprogram be generic?If the language allows nested subprograms, are closures supported?
narrowing conversion
converts a value to a type that cannot store even approximations of all of the values of origenal type
Pass-by-Result (Out Mode)
Require extra storage location and copy operation
Program Design Methodologies
New software development methodologies (e.g., object-oriented software development) led to new programming paradigms and by extension, new programming languages
Side Effects
Two possible solutions to the problem 1., Write the language definition to disallow functional side effects, No two-way parameters in functions, No non-local references in functions, Advantage: it works!, Disadvantage: inflexibility of one-way parameters and lack of non-local references; 2.Write the language definition to demand that operand evaluation order be fixed, limits some compiler optimizations, Java requires that operands appear to be evaluated in left-to-right order
Section 3
(5 cards)