nafarya/Kefetator

Interpreter for kef language. HW - compilers & interpreters

Kefetator

Interpreter for kef language. HW - compilers & interpreters

Documentation

All programs on Kef language start from function "main".

Variables declaration

Variable can be assigned with another variable or a number.

Syntax

[name] = [value | variable];

Variable names must match [a-zA-Z][a-zA-Z0-9]* regular expression and values must match [0-9]+

Example

x = 5;
b = x;
x123 = 15;

Conditional expression

Kef supports conditional expressions. Second if-branch is optional and can be omitted.

Syntax

if ([statement]) {
    ...
} else {
    ...
}

Example

Basic usecase

if (a) {
    a = a + 1;
} else {
    a = a - 1;
}

Omitted second if-branch

if (1) {
    x = 5;
}

Loop

Kef supports for loops with syntax cimilar to C. It has three optinal blocks:

• pre-action, executed once before loop body
• predicate, conditional expression to determine whether to execute current step of loop
• post-action, executed every time after loop body is executed

Syntax

for [preaction]; [forpredicate]; [forpostaction] {
    //for-body
}

Example

Count sum of numbers from 1 to 5.

n = 5;
sum = 0;
for i = 1; (i - n); i = i + 1 {
    sum = sum + i;
}
print(sum);

Functions

Functions declarations starts with func keyword, arguments are passed separated with spaces. All functions return number.

Syntax

1. name must start with [a-z], then can be [a-z] or [0-9]
2. args = Variable | Num | Function
3. returnValue = Variable | Num | Function

func name(args) {
    ...
    return returnValue;
}

Example

func mul(a b) {
    return a * b;
}

func main() {
    a = 2;
    b = mul(a 10);
    return b;
}

Print

print function outputs values to standard output

Syntax

print([statement]);

Example

a = 10;
b = 15;

func sum(a b) {
    return a + b;
}

func main() {
    print(5);
    print(a);
    print(sum(2 a));
}

Program examples

1. Read N from console and calculate factorial of N

func f(n) {
    if (n) {
        return n * f( (n - 1) );
    } else {
        return 1;
    }
}

func main() {
    n = readInt();
    print(f(n));
    return 0;
}

2. Read N from console and calulate N'th Fibonacci number

func is1(n) {
    if ((n - 1)) {
        return 0;
    }
    return 1;
}

func is0(n) {
    if (n) {
        return 0;
    }
    return 1;
}    


func fib(n) {
    if (is0(n)) {
        return 1;
    }
    if (is1(n)) {
        return 1;
    }
    return fib((n-2)) + fib((n - 1));
}

func main() {
    n = readInt();
    m = fib(n);
    print(m);
    return 0;
}

3. Read N from console and print squares of all numbers from 1 to N (inclusive).

func sq(n) {
    return n * n;
}

func main() {
    n = readInt();
    for i = 1; (i - n - 1); i = i + 1 {
        print(sq(i));
    }
    return 0;
}