01 Intro

Programming Lanugage¶

Tool for humans to communicate with a computer system

We should try to generalize a programming language, to ensure compatibility.

Properties¶

• Turing Complete Must be able to express anything computable
• Must be able to implement on existing hardware platforms

What makes a good language?¶

• Syntax close to what we are used to
• Readability
• Expressibility For eg, while loop instead of if and goto
• Reliability: Error Checking
  • Detect use of initialized variables
  • Type checking
  • Array Bounds (C vs Java)
  • Testing Support

Paradigms¶

Why do we usually use imperative languages?¶

As we mainly use von Neumann machines, which is the class of stored program digital computer.

Imperative languages give control over moving data and program instructions between registers in CPU and Memory location

von Neumann Architecture¶

There is no distinction between code and data, as they are stored in the same memory

Structured Programming¶

Dijkstra

Also referred to as ‘goto-less’ programming

• Single entry, Single exit sequence
• Selection
• Repetition

Generations¶

In the present-day, compiler-generated code is faster than human-written assembly code; it was not the case before

Bugs¶

Programming testing can be used to show the presence of bugs, but never their absence!

~ Dijkstra

Solution¶

• Organize code modularly, such that each part can be understood
• Alpha Testing by company testers
• Beta Testing by end-users

Early Programming Languages¶

Scripting Language vs Programming Language¶

Programming languages

• follow EBNF(Extended Bacus Normal Form)
• have CFG(Context-Free Grammar)

Language Translators¶

Compiled Code¶

flowchart LR

subgraph "Once"
  sp2[Source Program] --> Compiler
end

Compiler -->  tp2

subgraph "Every Execution"
    tp2[Target Program]
    i2[/Input/] --> tp2 --> o2[/Output/]
end

Interpreted Code¶

flowchart LR

subgraph "Every Execution"
    direction LR
  sp2[Source Program] --> Interpreter
  i1[/Input/] --> Interpreter --> o2[/Output/]
end

Virtual Machines¶

flowchart LR

subgraph "Once"
  sp2[Source Program] --> Compiler --> ip["Byte Code<br />(Intermediate Program)"]
end

ip --> vm[Virtual Machine]

subgraph "Every Execution"
    i2[/Input/] --> vm --> o2[/Output/]
end

combine the plus points of compiler/interpreter

Interpreting high level code is slow

Java¶

javac Prog.java
java Prog

Python¶

python prog.py

• First time the program is run, it is interpreted
• In subsequent runs, the cached byte code .pyc is executed

RAM¶

Random Access Memory

Stores program instructions, addresses, and immediate values

Shell Scripts¶

ls | sort | more

View resources consumption by various users

ipcs

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