Introduction To Programming Languages- CS471 -2

Most languages belong to one of these distinct paradigms

Imperative paradigm focus is on how the machine does what you want.
- Execution through state change.
- Key operation: assignment (side-effects)
Three key concepts
- variables
- assignments
- sequencing
Examples
- Structured control : C, Pascal
- Encapsulation: Modula 2, C++
- Object-Orientation: Smalltalk, Java
- Concurrency: Ada, Java, Concurrent Pascal

Functional language

Execution via evaluation (substitution and reduction of expression)

Based on formal computational model of lambda calculus

Key operation: function application

Examples:

eager evaluation: Lisp, ML, Scheme

lazy evaluation: Miranda, Haskel

Example of function style vs imperative style in Java

// computation via assignments
int factorial(n) {
   int fact = 1;
   for (int i = 1; i<=n; i++) {

       fact = fact*i; 
   } 
}

// functional style calls
int fact( int n ) { 
    if (n == 1) {
        return 1;
    } else {
        return n*fact(n-1); 
    }
}

Logic or constraint-based languages

Execution based on deduction

based on predicate calculus using a proof method called resolution

Robinson , A Machine-Oriented Logic Based on the Resolution Principle , Journal of the ACM, 12(1):23-41, January 1965.

attempts to find values that satisfy certain specific relationships, using a goal directed search through a list of logical rules.

Horn clauses and relations

Key operation: unification

Example: Prolog