1. Concepts of Programming Languages
Lecturer: Dr. Emad Nabil
Lecture # 2
Fall 2018

2. Influences on Language Design
Computer Architecture
Program Design Methodologies
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3. Influences on Language Design
Computer Architecture
Languages are developed around the prevalent computer architecture, known as the von Neumann architecture
Program Design Methodologies
New software development methodologies
(e.g., object-oriented software development)  led to new programming paradigms
new programming languages

4. Programming paradigms
Algol
Cobol
PL/1
Ada
Modula-2
Smalltalk C#
Python
Scala
Haskell ML
Mranda
APL F#
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5. Imperative programming Vs. Declarative Programming
Imperative programming languages
focuses on describing how a program operates.
a developer writes code that describes in exacting detail the steps that the computer must take to accomplish the goal. This is sometimes referred to as algorithmic / procedural programming. Ex (C#, Visual Basic, C++, and Java ) 
Declarative Programming languages :
is non-procedural and very high-level (4th generation).
focuses on what the program should accomplish without specifying how the program should achieve the result.
expresses the logic of a computation without describing its control flow.
Declarative programming often considers programs as theories of a formal logic, and computations as deductions in that logic space. EX:
database query languages (e.g., SQL, XQuery),
regular expressions,
logic programming (Prolog),
functional programming (Lisp, Haskell).
Markup languages (NOT Programming language)
It is a document format
Markup languages extended to support some programming (Java script)
Examples: HTML, XML

6. 1-Computer Architecture Influences on Designing programming languages
Well-known computer architecture: Von Neumann
Imperative languages most dominant, because of von Neumann computers
Properties of Imperative languages
Data and programs stored in memory
Memory is separate from CPU
Instructions and data are piped from memory to CPU
Basis for imperative languages
Variables model memory cells
Assignment statements model piping
Iteration is fast on von Neumann computers (faster than recursion)

7. The von Neumann Architecture

8. Von Neumann Bottleneck
Connection speed between a computer’s memory and its processor determines the speed of a computer
Program instructions often can be executed much faster than the speed of the connection; the connection speed thus results in a bottleneck
Known as the von Neumann bottleneck; it is the primary limiting factor in the speed of computers
instructions executed fast
Connection with memory is slow
von Neumann bottleneck

9. 2-Programming Methodologies Influences on designing programming languages
1950s and early 1960s:
Simple applications;
worry about machine efficiency (Fortran )
Late 1960s:
People efficiency became important; readability, better control structures
structured programming
top-down design and step-wise refinement (Basic)
Late 1970s: Process-oriented to data-oriented
data abstraction – (SIMULA) (Simula is the name of a simulation PL)
Middle 1980s: Object-oriented programming
Data abstraction + inheritance + polymorphism (Smalltalk)
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10. Language Design Trade-Offs
Readability
Writability
Reliability
Cost
Reliability vs. execution cost
Example: Java demands all references to array elements be checked for proper indexing, which leads to increased execution costs
Writability (flexibility) vs. reliability
Example: C++ pointers are powerful and very flexible but are unreliable
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11. Programming Languages Implementation Methods
1.Compilation
2. Pure interpretation
3.Hybrid Implementation Systems
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12. Programming Languages Implementation Methods
Compilation
Programs are translated into machine language
 such as C, COBOL, C++, and Ada,
Use: Large commercial applications
2. Pure Interpretation
Programs are interpreted by another program known as an interpreter
Use: Small programs or when efficiency is not an issue (PHP, java script)
3. Hybrid Implementation Systems
A compromise between compilers and pure interpreters
Used when efficiency is not the first concern
-(Java, .NET languages, python )
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13. Layered View of Computer
The operating system and language implementation are layered over
machine interface of a computer
Bare machine (or bare metal), in computer parlance, means a computer without its operating system. 
Macro instructions  BOIS
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14. 1-Compilation
Translate high-level program (source language)  into machine code (machine language)
Slow translation means fast execution (why?)
Ans: Code optimization takes time.
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15. 1-Compilation Compilation process has several phases:
lexical analysis: converts characters in the source program into lexical units
syntax analysis: transforms lexical units into parse trees which represent the syntactic structure of program
Semantics analysis: generate intermediate code
code generation: machine code is generated
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16. 2.Pure Interpretation No translation
Easier implementation of programs (run-time errors can easily and immediately be displayed)
Slower execution (10 to 100 times slower than compiled programs)
Often requires more space
Now rare for traditional high-level languages
Significant comeback with some Web scripting languages (e.g., JavaScript, PHP)
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17. 3.Hybrid Implementation Systems
1.Compilation
2. Pure interpretation
3.Hybrid Implementation Systems

18. 3. Hybrid Implementation Systems Just-in-Time Implementation Systems
JIT
Initially translate programs to an intermediate language
Then compile the intermediate language of the subprograms into machine code when they are called.
Machine code version is kept for subsequent (later) calls, each method is translated into M/C only when called.
JIT systems are widely used for Java programs (byte code)
.NET languages are implemented with a JIT system (.NET Common Intermediate Language (CIL)
In essence, JIT systems are delayed compilers
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20. Preprocessors in programming languages
A preprocessor is a program that processes a program immediately before the program is compiled.
Instructions to be used by the Preprocessor are embedded in programs. Like #include<iostream.h>
The preprocessor is essentially a macro expander. #include, #define
Preprocessor instructions are commonly used to specify that the code from another file is to be included.
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21. Programming Environments
A collection of tools used in software development
Microsoft Visual Studio.NET
A large, complex visual environment
Used to build Web applications and non-Web applications in any .NET language
NetBeans
Related to Visual Studio .NET, except for applications in Java
Source :
On March 2015
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22. Summary
The study of programming languages is valuable for a number of reasons:
Increase our capacity to use different constructs
Enable us to choose languages more intelligently
Makes learning new languages easier
Most important criteria for evaluating programming languages include: Readability, writability, reliability, cost
Major influences on language design have been machine architecture and software development methodologies
The major methods of implementing programming languages are: compilation, pure interpretation, and hybrid implementation