This simple programming language is part of a Computer Science course Theory of Automata at Lahore University of Management Sciences. Following is the comprehensive documentation of the programming language and its features.

YAPL has three atomic data types yet. These data types include

• Integers
• Floating point numbers
• Strings

YAPL can evaluate simple mathematical expressions. These include simple addition, subtraction, division, multiplication and modulus operations. If you want to write multiple expressions on the same line, they end with a semicolon otherwise single expression can be written per line.

In YAPL expressions can be added using '+' operator.

YAPL >>> 1 + 2
3

Subtraction can be done using '-' operator.

YAPL >>> 1 - 2
-1

Division can be performed using the '/' operator.

YAPL >>> 10 / 2
5

If division contains at least one floating point value, then the resulting value will be floating point value.

YAPL >>> 1 / 2.0
0.5

Multiplication between two expressions can be performed using the '*' operator.

YAPL >>> 12 * 2
24

The remainder of integer division can be obtained using '%' operator.

YAPL >>> 7 % 3
1

Multiplication, Division and Modulus operators have highest precedence in an expression by default.

YAPL >>> 1 + 2 * 3
7

However, the precedence of expressions can be changed by using paranthesis.

YAPL >>> (1 + 2) * 3
9

All programming languages need some kind of data storage mechanism to efficiently perform memory extensive tasks. YAPL can provide such functionality by storing fundamental data types in variables. A variable in YAPL can store any one of integers, floating point values and strings at a time.

In YAPL variables can be represented by names. Variable names always need to obey the following rules.

• Variable names cannot start with a number, special or non alphabetic character.
• Variable names must start with either an underscore or letters.
• Variable names can have more than one underscores or letters.
• Variable names cannot have spaces.

Variables in YAPL can be defined in two fundamental ways. The first method is type loose, which means that the data type for the variable is not fixed.

let number = 10

Here 'let' is a special keyword which defines a new variable called number. The number variable can now store any kind of value beyond this point. The let keyword declares a loosley type variable which can store any type of data during the course of execution and its scope. For example, after integer value of 10, the number can store a string value as well.

number = "hello world"

A variable can be declared without using the 'let' keyword but we have to specify a type specifier this time. This method will bound the variable to a specific data type and the variable can store only that kind of data over the course of execution and its scope.

int books = 10

The fundamental data types in YAPL are int, float, string, and char.

string message = "I love programming"

A variable can be assigned different values based on the type of the variable (either loose or fixed to a certian data type) many times as long as it is live in its scope.

int books = 0
books = 10

This statement puts a value of 10 in variable books which was already declared. Trying to put a data in variable which does not match its data type will create an error.

int price = 100
price = "ten" // this is an error

However, a loosley typed variable can store any kind of data. A more descriptive way of assigning a value to a variable in YAPL can be

put 100 in price

As such, any valid data can be inserted in a variable.

put (price - 50) in books // books now contain 50

Any good programming language gives the functionality of loops and so is YAPL. In YAPL we have three different kinds of loops each with several syntax types.

• For loop
• While loop
• Do While loop

In YAPL a for loop loops a certain (fixed) amount of time over a block of code. The syntax for it looks like

for (let counter = 0; counter < 10; counter++) { }

Here, the keyword for initializes the loop where the header cotains loop counter initiation, conditional checking at each iteration and increment of the counter. The body of loop that gets executed many times goes in braces. The paranthesis after for are optional. The above for loop can also be written like this

for let counter = 0; counter < 10; counter++; { }

But watch for the additional ; after increment statement. The counter can be incremented or decremented in any way.

for let counter = 0; counter < 10; counter += 2; { }

Another way to write a for loop in YAPL can be

for (1 to 10) { }

Again the paranthesis are optional. This kind of loop can take step as an additional argument.

for 1 to 10 step 2 { }

Loops can also go from high value to low value

for 10 to 1 step -2 { }

Here the numbers can take place of any valid variables

let counter = 0;
for counter to counter + 100 step 1 { }

While loops in YAPL are very simple. They contain a keyword while followed by some condition and then a body of loop.

while (counter < 5) { }

Again the paranthesis in conditional statement are optional.

Do while loop differ from while loops in a sense that they run at least one time. The YAPL syntax for do while loops look like

do { } while (counter < 5);

Here the paranthesis and semicolon are both optional.

In YAPL there is a support for conditional statements. The type of conditional statements supported by YAPL are

• If statements
• If Else statements
• If Else If statements