CSCE 314 Lecture 1

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Programming Languages

Languages for instructing computing devices

Different approaches to describe functions:

• Imperative
• declarative
• functional

Communicate Ideas between humans (human-readable), but unambiguous

Level of Languages

• Lowest level: machine code (0's and 1's)
• Assembly: Giving registers and values names
• C
• Scheme, Java
• Haskell, Prolog
• Natural Languages
• Ruby, Gerkin ;)

History Follows very closely:

• 1940: connect wires to represent 0s and 1s
• 1950: Assemblers, FORTRAN, COBOL, LISP
• 1960: ALGOL, BCPL (B and C followed), SIMULA
• 1970: Prolog, ML
• 1980: C++
• 1990: Haskell, Java
• 2000: D, C#, Spec#, F#, Cω, Scala, Ruby!
• 2020: Intentional Programming?

Defining a Language

Syntax and Semantics:

Syntax

Set of valid programs (usually represented by grammars

<if-statement> ::= if <cond-expression> then <statement> else <statement>

Semantics

The meaning behind the parts of a program:

if-statement ::= if condition then true-statement else false-statement

Language Implementation

Undo the abstraction from source language:

int i;
i = 2;
i = i + 7;

to assembly/byte-code:

0 iconst_2 // put integer 2 on stack
1 istore_1 // store top of stack to location 1
2 iload_1  // read value at location 1 on stack
3 bipush   // put value 7 on stack
4 iadd     // add 2 stack values and push to stack
5 istore_1 // store at location 1

to machine code:

01110101001000101010101100111010001001101011110100000010110100110000100101110101

Languages could be immediately interpreted at the AST phase, compiled to byte code and run on a virtual machine, or compiled all the way into machine code.