AquaScript

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AquaScript is a procedural programming language developed for learning about compilers theory. Despite the script term in its name, it is a compiled programming language.

Definition

AquaScript is a very simple language that have a tipical definition of C-Like languages. See below the allowed notation:

• Flow controllers if, else and for;
• Arithmetic operators +, -, *, / and %;
• Conditional operators =, <, >, <=, >= and !=;
• Logical operators and, or e !
• Increment ++ and decrement -- operators;
• Reserved words return, read, write, break and null;

Typing

AquaScript is a loosely typed language and only handles number, text, and bool types. It is also statically typed, so the values assigned to a variable do not change during program execution. In AquaScript there are no implicit or explicit casting. As the project advances, it is possible that this will be implemented in the future.

Syntax

The AquaScript syntax was built to be very simple and familiar to the programmers used to other languages. It dispenses with the use of a starting point for the program, making the reading of the program depend on the order in which the statements are made, similar to what happens in scripting languages like JavaScript or Python.

See below the syntax definition in Backus-Naur Form:

program  ::= statement*

statement
         ::= if
           | for
           | attribuition
           | singlinecomment
           | multilinecomment
           | ( increment | decrement | return | read | write | 'break' ) ';'

if       ::= 'if' '(' expression ')' body

for      ::= 'for' '(' attribuition? ';' expression? ';' attribuition? ')' body

attribuition
         ::= 'id' ':' ( function | expression ';' )

singlinecomment
         ::= '//' [^\n]*

multilinecomment
         ::= '/*' ( [^*] | '*'+ [^*/] )* '*'* '*/'

increment
         ::= 'id' '++'

decrement
         ::= 'id' '--'

return   ::= 'return' expression?

read     ::= 'read' 'id'

write    ::= 'write' expression

function ::= '(' param? ')' body

expression
         ::= side ( ( '<' | '>' | '<=' | '>=' | '!=' | '=' ) side )? ( ( 'and' | 'or' ) side ( ( '<' | '>' | '<=' | '>=' | '!=' | '=' ) side )? )*

param    ::= 'id' ( ',' 'id' )*

body     ::= '{' statement* '}'

side     ::= term ( ( '+' | '-' ) term )*

term     ::= unaryexpr ( ( '*' | '/' | '%' ) unaryexpr )*

unaryexpr
         ::= ( '+' | '-' )? factor

factor   ::= bool
           | 'number'
           | 'text'
           | 'id'
           | 'null'
           | '(' expression ')'

bool     ::= 'true'
           | 'false'

See the AquaScript Syntax Diagram generated by definition described above.

Examples

Variable declarations

Variables in AquaScript are always initialized to some value. The assignment operator is the : (colon), as if we were seeing the attribute of an object in JavaScript.

a: 3; // a receives the value 3 and is of type number
b: 4.5; // b receives the value 4.5 and is of type number
c: a + b; // c now worth 7.5

d: "Foo";
e: "bar";
f: d + e; // f is of type text and has the value "Foobar";;

g: true; // g is of type bool and is true
h: !g; // h is of type bool and negates g - false
i: g or h; // i is of type bool and is true

Function declarations

Function declarations in AquaScript are done differently from other languages like C or Java. Naming functions is like giving them nicknames through variables, as shown below:

<function_name>: (<parameters>)
{
	// body
}

See below some examples.

Hello World

write "Hello, World!";

Say hello

say_hello: (name)
{
	write "Hello, " + name + "!";
}

say_hello("Petter"); // Output: "Hello, Petter!"

say_hello: (name)
{
	return "Hello, " + name + "!";
}

write "Enter a name: ";
read name; // Read an user input

write say_hello(name);

Factorial

factorial: (x)
{
	if (x < 2)
	{
		return 1;
	}

	return x * factorial(x - 1);
}

write factorial(5); // Output: 120

The Bigger

the_bigger: (x, y)
{
	if (x > y)
	{
		return x;
	}
	else
	{
		return y;
	}
}

write the_bigger(5, 6.5); // Output: 6.5

Is Prime

is_prime: (x)
{
	count: 0;

	for (i: 0; i < x; i++)
	{
		if (x % i = 0)
		{
			count++;

			if (count > 2)
			{
				return false;
			}
		}
	}

	return true;
}

write is_prime(4); // Output: false
write is_prime(7); // Output: true

Roadmap

So far, the AquaScript compiler even performs the parsing phase of the source code. As a next step, its semantic analyzer will be developed.

Contact

For questions or clarifications, send an email to [email protected].

License

MIT Copyright (c) 2018 Davidson Bruno da Silva