Gossip Syntax

Gossip is a dynamically typed, interpreted programming language. This document specifies the syntax of the language.

General Syntax

All statements in gossip compulsorily end with a semicolon. Variables are dynamically typed, and typechecked with a typechecker. Variables, once identified by a type during declaration, cannot be assigned values of other datatypes.

declare a = 9;
print(a);

print(123812073);

assign a = 123;
print(a);

declare t = 5;
print(let r = 100 in let t = 10 in r + t ; ;);

We recommend writing Gossip code as closely as possible to python’s PEP-8 standards; explicitly, we recommend spaces between operators and operands, declaring variables near the top of the codebase, and separating semicolons in the middle of a line with a whitespace.

Data Types

Gossip has a number of built-in data types: NumLiterals, Booleans, StringLiterals, and Lists.

Numbers

Numbers in Gossip can be integers or floating-point numbers. They can be written in decimal notation. Here are some examples:

10
3.14

In Gossip, all numbers are inherently handled as Fractions, so 2.5 is actually the simplified fraction 5/2, and is calculated as such.

Booleans

Booleans in Gossip are True and False, and can arise both explicitly or as the result of a boolean operation.

Variables

Variables in Gossip are dynamically typed, which means that they can be assigned values of any type. A variable is declared using the declare keyword. Here is an example:

declare x = 10;

Once declared, a variable cannot be re-declared in the same or a child scope. Forward declarations are not allowed, and changing values requires the assign flag.

assign x = 20;

Once declared with a value, the variable is bound to be assigned values only of that type. This extends to Numbers, Booleans, Strings and Lists.

declare x = 20;
assign x = 'abc';

The above code would throw an error related to Bad Assignment of variables.

Strings

Strings are defined the same way as numbers, and are written exclusively with single quotes (‘). Strings support indexing, concatenation and slicing operations.

Concatenation

declare x = 'Hello World!'
assign x = x+x 
print(x)

This prints out HelloWorld!HelloWorld!, as is expected. Strings cannot be operated upon with numbers.

Slicing

The slice operation takes two indices- the start and the end index. Sliced portion of the string is in the index range [start,end).

declare i = 1;
declare word = 'abcdefghi';
print(word[i,i+3]);

This prints out the characters in the string from index 1 to index 3 - bcd.

Indexing

This is used to access the character at a particular index in the string. Gossip follows 0-indexing (the first index value is 0 and increments by 1).

declare i = 1;
declare word = 'abcdefghi';
print(word[i+3]);

This prints out 'd'- the element at index 4.

Lists

Lists are declared and assigned using similar methods as other datatypes.

declare x = [1,2,3,4,5];
declare y = ['abc','def','ghi'];
declare z = [True, False, True];

Lists support five operations - head, tail, empty, cons, indexing, slicing.

Head and Tail, Empty

Head returns the first element of a list. Tail returns a list of all elements except the first element. Empty checks whether a list is empty or not. It returns True when it is, and False otherwise.

print(x.head);
print(x.tail);
print(x.empty);

This prints out 1, [2,3,4,5], False

Cons

This method is used to add an element to the head of the list. Lists have fixed types. So, attempting to add an element having type different from those already in the list would throw an error.

x.cons(29);
print(x);

This prints out [29,1,2,3,4,5]

x.cons('abc');

This throws an error.

Indexing

This is used to access elements at a particular index in the list. Gossip follows 0-indexing (the first index value is 0 and increments by 1).

declare l = ['abc','def','ghi','jkl','mno'];
declare ind = 1;
print(l[ind+2]);

The above code prints 'jkl' as it’s output.

Slicing

The slice operation takes two indices- the start and the end index. Sliced portion of the string is in the index range [start,end).

declare i = 1;
declare l = ['abc','def','ghi','jkl','mno'];
print(l[i,i+3]);

This prints out the characters in the list of elements from from index 1 to index 3 - ['def','ghi','jkl'].

Operators

Gossip has several built-in operators.

Arithmetic Operators

Gossip has the following arithmetic operators:

+ - * ** / %

Here is an example:

10 + 5 * 2

The + operator is overloaded to also work on Strings, where it handles concatenation.

Comparison Operators

Gossip has the following comparison operators:

< > <= >= == !=

Here is an example:

10 < 20

These return a boolean value, that can be used to evaluate an If-Else construct.

Logical Operators

Gossip has the following logical operators:

and or not

Here is an example:

a > b and a < 2*b

Assignment Operators

Gossip has two assignment operators:

declare assign

Here is an example:

declare x = 10;
assign x = 20;

Control Flow

Gossip has the following control flow statements.

If Statements

An if statement in Gossip looks like this:

if a < b then{
x = 10;
} else {
x = 20;
};

While Loops

A while loop in Gossip looks like this:

while x < 10 do {
x = x + 1;
};

For Loops

A for loop in Gossip looks like this:

for i in range 1 to 10; do {
print(i);
};

Repeat Loops

A repeat loop in Gossip looks like this:

repeat{
x = x + 1;
} until x == 10;